| The Sustainable Energy Handbook for NGOs and Local Groups |
Translated and edited by Ann Vikkelso, Copenhagen Environment and Energy Office & The Danish Organization for Renewable Energy
Associated Energy and Environment Offices
The Danish Organization for Renewable Energy
Denmark, September 1993
Sustainable Energy Handbook - for NGOs and local groups
Associated Energy and Environment Offices
c/o Viborgegnens Energy and Environment Office
Dumpen 6, DK-8800 Viborg, Denmark
Ph: +45-8661 2322. Fax: +45-8661 4146
ORGANISATION FOR RENEWABLE ENERGY
SEKRETARIAT OG TIDSSKRIFT
Dannebrogsgade 8 A
8000 Arhus C
Tlf.86760444 Fax 86760544
Ann Vikkelso, Copenhagen Environment and Energy Office & OVE
OVE Europa Projektkontor
Gl. Kirkevej 56, DK-8530 Hjortshoj, Denmark
Ph: +45 86 22 70 00, Fax: +45 86 22 70 96
Karsten Plejdrup, Associated Energy and Environment Offices & Viborgegnen's Energy and Environment Office
Anders N. Andersen, M.Sc, H.D
Associated Energy and Environment Offices
Ann Vikkelso, M.Sc. (eng.)
Copenhagen Environment and Energy Office
Jan Viegand, M.Sc. (eng.)
Gunnar B. Olesen, M.Sc. (eng.)
Jens H. Larsen, M.Sc. (eng.)
Erik Lund, Architect
Bakkelandet's Energy Office
Hans Jakob Jakobsen, Architect
Aarhus Energy and Environment Office
Ole Rahn, Electrician
Viborgegnen's Energy and Environment Office
Ole Elmose, Folk High School Teacher
Ole Skadborg, M.K.
Lars Helbro, Energy Advicer
Himmerland Energy Office
Christian Scholten, M.Sc. (eng.)
Danish Wawe Power
Kim Nielsen, M.Se. (eng.)
The handbook is translated into the following languages:
Jak Oszczedzac Energie ?, Poradnik. Prof. dr hate inz. Kazimierz KURPISZ & dr
inz. Janusz SKOREK, Technical University of Silesia, Gliwice. ISBN 87-87660-
Energie - Kde Ji Vzit?, Prirucka. Jiri Beranovsky, EkoWatt, Praha. ISBN 87-
Energia K'zikonyv. Kovacs ?va & Kovacs Karoly, Reflex, Gyor. ISBN
Energia Kasiraamat. Anu Lausmaa, TAASEN, Tallinn. ISBN 87-87660-77-6
Rabochaia Kniga Energeticheskogo Ofisa.' Vladimir Shestakov, Citizen
Initiative, St.Petersburg. ISBN 87-87660-78-4.
The Project is supported by: National Agency of Environmental Protection (Denmark) Subsidies for Environmental Activities in East European Countries.
This handbook is based on the experience gained by the Danish Energy and Environment Offices during the last 10-15 years' work for a mote sustainable energy system. Energy advisers from several of the 24 local Danish offices have contributed to the book.
The handbook is ment as inspiration and a tool for other NGOs (Non Governmental Organizations) and local grassroot groups in Europe.
It has been translated into Russian, Estonian, Polish, Hungarian and Czech language by representatives from local Energy NGOs and it is distributed in these countries.
We would like to thank the National Agency of Environmental Protection, Denmark (Subsidies for Environmental Activities in East European Countries) that has supported the project.
Denmark, September 1993.
Ann Vikkelso, Copenhagen Environment and Energy Office & OVE
Karsten Plejdrup, Associated Energy and Environment Offices
The energy offices are local groups that promote and inform on renewable energy and energy efficiency. They initiate projects in the local society and try to influence local politics.
Anders N. Andersen, chairman of Associated Energy- and Environment Offices
Denmark is known internationally for the popular involvement and participation in the implementation of energy and environment action plans, and known for a very fruitful dialogue between central planners and local energy and environment groups. The central planners are often divided into traditional sectors; but exactly cooperation, dialogue, and debate, between local impartial energy movements and the central planners from administration, power utilities, and gas utilities, have encouraged sustainable overall solutions across the usual sector borders.
In an energy and environment framework there are good reasons for gathering in local associations, in order to promote energy and environmentally conscious solutions locally. Often people carry out small cogwheel functions in their daily work, where they only have limited possibilities to get insight in, and influence the complicated relations, which creates many of the present environmental problems. For many people, the daily cogwheel function is not enough to complement their life. They wish to take active part in promoting a sustainable development in their neighbourhood. By joining forces with other interested people, they gather a considerable interdisciplinary knowledge, thus the members of Danish energy and environment offices are taking part in promotion of sustainable overall solutions across the usual sector borders.
It is not a coincident that local energy and environment groups in Denmark are organized as associations. In Denmark there is a good joke telling that two Danes can not meet without starting an association. The right to establish associations, is a constitutional right in Denmark (the Constitution Ã¤78,1 reads: "The citizens have the right to form associations for any legal purpose without previous permission"). The Danish energy and environment offices have received public finances for several years, which has made it possible to rent office space, and employ staff. The staff at the local energy offices have independently managed information and implementation in the energy field, and has furthermore coordinated local activities on energy and environment.
The local energy and environment offices are organized in Associated Energy and Environment Offices (SEK) and have a written agreement with SEK on the utilization of the state subsidy. The agreement guarantees strong local efforts, and a high degree of self administration, at the same time as a fully satisfactory use of the public money is guaranteed. During the last 10 years, a well functioning cooperation has been built up between the local energy and environment offices through SEK. Considerable organisational, administrative, and technical experiences have been built up at the individual energy and environment offices, partly based on this cooperation.
Amongst other things, this handbook aims at spreading these organisational, administrative, and technical experiences to new energy and environment offices. The handbook sets clear parameters for the organisation and administration of an energy and environment association. In this way, it helps to visualize that a local, democratic organized energy and environment association takes part in solving the problems of modern society, just as efficient as other kinds of organizations. The technical parts of the handbook illustrate that it is necessary to work within a broad technical spectrum, when we want to point out the best solutions.
Ann Vikkelso, Copenhagen Environment and Energy Office Anders N. Andersen, chairman of Associated Energy and Environment Offices
An energy and environment office is a local association, which provides free, impartial information and guidance on energy conservation and utilization of renewable energy sources. At the same time the energy offices initiate many energy and environment activities in their local areas. Today there are 19 energy and environment offices in Denmark. 12 of these are subsidized by the Danish Energy Agency for their educational work on energy. Most of the offices employ one or more energy advisers, who are responsible for the daily work.
The size of the local energy and environment offices ranges from 20 to 500 members. The members are, in addition to households, wind turbine cooperatives, cooperative building societies, firms, farms, folk high schools, etc. A smaller fraction of these are more closely connected to the office, and participate to some extent in the office activities.
The activities of the local energy and environment offices also depend very much on the location. The city offices are often involved in city ecology projects, as well as water saving and traffic planning are natural tasks. In the country a main work field is utilization of biomass. - And in West Jutland one of the more common tasks is establishment of wind turbine cooperatives, but also the rest of Denmark is catching up in that field.
An energy and environment office is usually started by a group of people in the local area, who gather and form an association with the common aim to promote environmentally friendly energy solutions. The initiators are mostly enthusiastic people who are already involved in energy and environment activities; but in this way they strengthen their work. The first energy and environment offices are more than 15 years old, while the newest has existed less than a year.
In the beginning the offices worked mainly with technical questions in connection with utilization of wind and solar energy. This was before fully developed products existed on the market, and every job was almost a small development project. But concurrently with the development of wind turbines, solar heaters, biogas plants, etc., the tasks of the offices have changed during the last years. The offices now work more with the interaction between all the different things that influence the energy consumption: domestic heat consumption, possibilities for electricity conservation, waste management, water savings, transport structure, etc. Put shortly Green Planning.
Therefore many of the offices have changed their name from Energy Office to Energy and Environment Office. The main task is still to inform on, and initiate renewable energy, which is the part of the work that gains subsidy for the time being. But this work is now connected to all the other factors in the planning that must follow, if it shall make any sense to aim at covering a larger part of the energy consumption by renewable energy.
The energy and environment offices have taken on a large task: to make the society function environmentally sustainable. A lot of resources are needed to make it happen - much more than are available today. Thus the Danish energy and environment offices work on establishing several Green Offices together with other Danish organizations dealing with energy and environment.
It is common for the energy and environment offices to have a local association with a board standing behind them. One of the most important tasks for the board is to give inspiration to, and initiate, local work. The energy advisers, who are easily buried in the extensive day-to-day work, need visionary partners. Furthermore the board has some more formal tasks, which are described in chapter 3.
Many offices have a background group or activists who support the daily work. They may give technical assistance to solve different problems, be responsible for the newsletter from the energy and environment office, etc. If this high degree of local involvement did not exist, it would be difficult to keep the energy and environment offices alive.
The energy and environment offices are strongly connected to other activities on energy and environment in their local area. For example West Zealand E;nvironment and Energy Office is located nearby an experimental Green City area. The area contains different buildings and other initiatives in the field of green planning, and shows how building and energy designs can be made with regard to future generations. The office has been involved in some of the projects in the area. Another office is neighbouring the Folkecenter for Renewable Energy. This location enables them to show demonstration plants and test plants, that are built at the place.
The energy and environment offices cooperate with other environmental groups in the neighbourhood. Likewise cooperation with local firms and tradesmen (e.g. plumbers who install solar heaters) is a natural part of the offices' work. Another important task is the cooperation with local politicians and authorities; and of course political work at local level to promote environmentally friendly energy solutions. - It is unfortunately not always the case that local politicians agree with us.
Energy and Environment Office Activities
The energy and environment offices use many methods in their work to promote renewable energy, energy savings, and other green solutions.
Free educational, information, and consultancy activities
Everybody is welcome to contact the offices, either personally or by phone during opening hours, with questions about everything related to renewable energy and energy savings. The energy adviser is often able to give an answer immediately, or has written material that is sent to people who apply.
The opening hours and staff at the individual offices depend on, if the office receives financial support, or the activities solely are based on subscriptions and voluntary work. The energy and environment offices that receive core funding from the Danish E;nergy Agency, employ an energy adviser and have fixed opening hours.
The offices answer all inquiries. If the individual office can not answer on the spot, it is in contact with other energy and environment offices and other competent persons it can lean on. So in most cases the answer can be found within a few days.
The energy and environment offices often organize exhibitions in the local area. Most energy and environment offices have carried out solar energy campaigns together with local plumbers.
Public lectures, debates, conferences, and meetings, are other methods the energy and environment offices use to disseminate information. They can either take place at the office, or a representative from the office visits a school or a meeting hall, and gives a lecture; for example on solar heating, wind power, or low energy building. These meetings are advertised in the daily newspapers.
Publication of a newsletter, books, magazines, booklets, etc. The energy and environment offices stay in contact with their members through a local newsletter, that is issued four to six times a year.
Presentation of plants and demonstration houses Many energy and environment offices arrange open house days once or several times a year, where it is possible to visit wind turbine cooperatives, biogas plants, a family with a solar collector on the roof, plants for collection of rainwater, etc.
Resource audit of the house
Members of the association can have a visit from an energy adviser, who examines the house. Based on the audit, the energy adviser will recommend electricity, heat, and water saving measures, e.g. installation of renewable energy plants, recycling, etc. See also chapter 4.
The energy and environment offices also spend some time on teaching in primary schools, adult education centres, day classes, etc. The education can be either on a specific topic, or in general on renewable energy and various environmental conditions.
Demonstration plants, plus research and development projects
The energy and environment offices act as initiators and consultants in larger projects. But the extent of these activities is very dependent on which skills the active members of the individual association have.
Some energy and environment offices undertake paid consultancy, by virtue of specially qualified staff, either employees or in the background group. They take part in realizing different types of renewable energy projects - e.g. large wind turbine projecs, biogas plants, or building renovation. But in the majority of cases, the role of the energy and environment offices is to promote and bring the ideas into effect. The practical implementation is thereafter done by local tradesmen, or for larger projects by a consulting engineer.
The Energy Adviser
Most energy and environment offices have a permanently employed energy adviser. She is responsible for the daily management of the office. In addition her work is to give free and unbiased advice - mainly to private people - on supply of renewable energy sources, and energy saving measures, etc. But also institutions can of course approach the office.
The energy adviser has usually acquired her knowledge through active involvement in development and implementation of renewable energy plants. She is experienced in information search and hearing of authorities, and has often a technical, trades, or other similar background. In addition the energy advisers have completed some courses on renewable energy, and they currently follow in-service courses and other technical cooperation organized by Associated Energy and Environment Offices.
An energy adviser can not be expert in all fields. But the expertice at the individual energy and environment office does not only depend on her, but also on the background group. If there are special requirements that can not be met by the energy adviser or the background group, contact can be made to another energy and environment office with expertice in the specific field.
1. Energi ska' der til, energikontorsavisen (Energy is a must, the energy office paper). Information paper published by Associated Energy and Environment Offices, 1992.
3. Organizational structure of an energy and environment office
Anders N. Andersen, chairman of Associated Energy and Environment Offices.
Regulations of the Association
There are good reasons to remember that articles are not made to regulate the cooperation between the members of the association during good times. As long as everybody gets along, the need for regulations is very limited. The right solutions can be found through discussions. But when problems appear, e.g. in a situation that a staff member has to be fired, one of the members harms the good name of the association, or there are economical problems, then it is important to have thoroughly made articles that precisely describe how to solve the problems. Beneath is described what needs to be in the articles.
It is fine to start a local energy and environment office without precise articles. But as long as the articles do not bother the daily work, there may be good reasons to prepare for bad times where it is relevant to have clear and precise articles.
The Purpose of the Association
The purpose of the association must be that precise, that people who join the association are sure they meet others who are working toward the same goal.
In the articles for the energy and environment offices it is stressed; to promote the change-over of energy supply to renewable energy? and to promote the change-over to a sustainable development that considers the ecological balance.
Another main purpose is that the association's work must be impartial. For example when renewable energy is promoted, it will often involve installation of energy plants. But an energy and environment office is not only a sales office for a certain manufacture. The local citizens must be sure that advice from their energy and environment office are not caloured by money from manufacturers. The activities of the energy and environment offices will of course often result in extra work to manufacturers of energy and environment devices, but it must never be doubted that the energy and environment office is the consumers' advocate in cases with possible conflicts of interests.
In the article on members it is pointed out that the annual subscription must be paid in time, before one is considered to be valid member with rights, e.g. to vote at general meetings.
In one of the first articles it is stated that members of the association are not personally liable for any debt of the association. This statement is important, as it may keep many away from taking part in the activities of the association, if there is a risk, that they personally can loose a considerable amount of money through their participation in the activities.
The general meeting is the highest authority of the association.
There is one ordinary general meeting every year. There may be a need for additional general meetings. The articles clarify who is entitled to call a general meeting, and which time limits that hold good the call.
The general meeting can not make decisions on matters, that are not on the written agenda, which has been sent out. This is a good rule, that enables the members to assess, if the items on the agenda are that important, that they want to participate. It also gives the members a chance to prepare for the general meeting.
Proposals on changing the article and not be carried with a small majority. To change the articles at least 2/3 of the attending members must vote for it. The articles of the association must be difficult to change, so they form a steady basis for the daily work in the association.
It is stated in the articles, that the general meeting elects the board, and the day-to-day head is employed by the board. It is a good idea, that only half of the board members come up for election every year, in order to establish continuity in management. To some degree, this also secures against coupe. E.g. if a non-representative minority of the association turns out in strength at a general meeting, this minority can in principle take over the association at the general meeting. When only half of the board is changed, it secures against a total takeover.
The day-to-day head must follow the guidelines and recommendations given by the board. And the day-to-day head can not make decisions, that are extraordinary or of great importance for the association.
The association is bound by agreements entered by the day-to-day head or the chairman together with another member of the board.
The auditor must not be dependent on the people, that are regularly at the energy and environment office.
Expulsion of Members
It is very seldom necessary to expel a member from the association. But there ought to be rules for, how to manage the situation, if it appears. One way, is to have rules on that members, who to considerable extent act against the purpose of the association, can be expelled by the general meeting.
It is natural that the day-to-day head or the board can not expel a member, the expulsion can solely be effected by the general meeting. If the board was allowed to have expulsion right, the theoretical situation could be, that the board expelled its general meeting, which is contradicting that the general meeting is the highest authority of the association.
Closure of the Association
There must be a considerable majority, to close down the association. But if it is finally decided to close down the association, there ought to be rules stating, that any property of the association does not just go to the last members, but goes to organizations that are working for the same goals as the association on a non-commercial basis. This also removes a possible reason for new members to wish to take over the association.
Generally on Change of Articles
As mentioned before, it takes a vast majority to change the articles. But there is in general, according to Danish practice of rules for associations, a tradition to give the minority of the members considerable protection, also if the protection is not directly stated in the articles. Amongst other things this means that there are some changes of articles, which can never be carried out, even if they are decided by a sufficiently large majority. A Danish lawsuit, started by an injured minority, will in many cases overrule the change of articles. Minority protection might be evident in cases, where a change of the articles was suddenly made, so that a few persons are liable of the association's debt, or some of the members lost their right to vote at the general meeting.
General meeting is the place, where members of the association can most directly influence the activities of the association.
General meeting is the highest authority of the association, and it is at the general meeting, the board is appointed, and through this get the legitimacy to act on behalf of the association.
It is important that as many members as possible show up at the general meeting, and the board will often arrange open house or lectures on topical energy and environment questions, to make it more interesting to participate in the general meeting.
It is important that the general meeting is carefully planned, and goes off in a way that is acceptable for the members. The chair person has a decisive role in getting through the general meeting. The chair person's tasks are described beneath. Written votes are used to make decisions, when there is no consensus.
The Chair Person's Task
It is crucial that the chair person is the general meeting's man. The chair person is considerably responsible for, that the decisions supported by the majority, also are the decisions that are finally adopted.
The chair person has considerable influence on how the general meeting goes off, and it is therefore decisive that a qualified chair person is chosen. The demands to a chair person include amongst other things:
1. Knowledge on the association's regulations and any rules of procedure.
2. Best possible knowledge on the topics, that will be discussed.
3. Impartiality in all decisions. Even though the chair person is chosen by the majority, he is also the protector of the minority.
4. Best possible knowledge of the association's members.
After the chair person is chosen he must:
1. State that the general meeting is legally called. If there are shortcomings, he will announce them, and the consequences of carrying the general meeting through under these conditions. Thereafter he will ask for the meeting's support to carry the general meeting through anyway.
2. State that the general meeting forms a quorum. 3. Read out the agenda.
If there will be a vote on a concrete proposal, which either can be adopted or rejected, then most people will feel that, if a simple majority vote in favour of the proposal, then the proposal is adopted.
The task gets at once more difficult, when the board has to be elected. It is important that the board represents all members. The election of the board must fulfil the following claims:
1. The candidates, which the majority of the association's members prefer, shall be elected.
2. A minority of a certain number must have the possibility to be represented in the board.
3. All members and substitutes of the board must be appointed in one and the same round.
4. The voting system must be easy to explain.
It is important that the board is elected democratically and representatively. The claim on representation also of minorities will probably be met by sympathy by most members. If 5 members will be elected for the board, then 1/5 of the members of the energy and environment office should be able to have their favourite candidate elected for the board.
If the meeting is ready to vote many times, then more fair and democratic procedures for the vote can be figured out. But there are often many questions on the agenda, so it is important to limit the vote to one or two rounds.
It is an ongoing task of the board to lay down guidelines and instructions, which the day-to-day head has to follow. Furthermore the board plays an important role as initiator of activities. The day-today head can not make decisions that are extraordinary or of great importance for the association, such decisions have to be made by the board.
In general the tasks of the board can be summarized:
1. The board must secure that the activities of the association are within the association's purpose.
2. The board must secure that regulations of the association are respected.
3. The board must secure that regulations of the association are currently updated.
Responsibilities of the Board
The board of a Danish energy and environment office has moral responsibility to inspect that no irregularities are committed in the daily work. Irregularities at one energy and environment office may result in bad reputation of other energy and environment offices, and thereby make their work difficult.
In addition to moral responsibility, there may also be an economic responsibility in two cases.
Fraud: The board can be held personal responsible for fraud by the day-to-day head, if it can be proved that the board has neglected its supervising duty.
Violation of existing law: When the existing law is violated, they can be fined. There are several possibilities. The association can be fined, the day-to-day head can be fined, the association can be fined, or some combination of these. In all cases the fine has to be paid by the one, who is fined. Thus the board cannot pay personal fines with money from the association, whether they have known about the violation or not.
Ann Vikkelso, M.Eng., Copenhagen Environment and Energy Office
Consumption of energy is not an objective itself. Huge energy consumption is not necessarily a sign of high material living standard. It is instead the so-called energy services - light, a warm living room, food, etc. - we are satisfied by.
It is important that we discuss our demands and become clear about which energy services we want to fulfil. Then we can evaluate which is the best way to obtain the desired energy services - for example we do not need an electrical hairdryer to get dry hair.
Energy chains can be set up on how to obtain different energy services. Figure 4.1 shows an energy chain for energy services in general. The starting point - primary energy - can be fossil fuels, renewable energy, uranium, etc. This is converted into secondary energy (e.g. wind turbine producing electricity), which is used by the consumer (e.g. in a low energy light bulb), or in industry for producing goods (e.g. a low energy light bulb), which also ends with the consumer.
It is important to evaluate the chain in total, if we want to decrease energy consumption. A good example is fresh air in Danish cowsheds which is traditionally provided by large ventilation systems. It is of course possible to lower the energy consumption by improving the motor and ventilator. But another possibility, at experimental stage, is to replace the ventilator with an automatically controlled damper, thus totally skipping one link the electricity consuming ventilator /1/, figure 4.2.
Another example is electrical lighting. In figure 4.3 the last part of the energy chain for light on a desk is shown (it is not taken into consideration how power is produced). Obviously the source of light (incandescent lamp, low energy light bulb, ...) is not the only thing influencing the light efficiency. It is also of great importance what kind of shade is chosen, and if it is kept clean, etc.
If we want to compare the environmental impact from different technologies, a life-cycle analysis also called cradle to grave analysis - must be made. It consists of an evaluation of resource consumption and environmental impact caused by production, operation and phasing-out of the technology.
A check list on the content of life-cycle analyses can be set up /2/:
Emissions and environmental impacts
Energy and resource consumption
Emissions and environmental impacts
Energy and resource consumption
Emissions and environmental impact
Low energy refrigerators are a good example of why it is important to consider the above mentioned factors in an analysis. Low energy refrigerators produced in Denmark have a thicker insulation layer than ordinary new refrigerators. The insulation used at the moment contains CFCs, which severely contribute to the green house effect and deplete the ozone layer. Fine enough, that the green house effect decreases due to decreased electricity consumption (simultaneously decreases coal consumption in Denmark), but this is partly counterbalanced by the CFC emission that slowly comes from the insulation. Though it must be mentioned that the total effect is positive, and methods for destruction of the CFC in the insulation material are nearly ready /21. Likewise refrigerators without CFCs are on the way.
General Energy Analyses
General energy analyses are limited to factors influencing the energy consumption, but still cover the full life-cycle for a certain technology. In a total energy analysis energy consumptions are compared to achieve a certain out-come (electricity, heat, lighting, etc.). When the energy consumption at the different stages is evaluated, it is important to remember all kinds of energy use; including energy used: for mining of raw materials, by sub-contractors, for running pumps in renewable energy installations, for fuel transport, etc.
In figure 4.4 and 4.5 renewable energy technologies are compared to fossil. It is visible, when comparing fossil (primary) energy consumption for construction and operation, that renewable energy technologies are much less polluting.
Energy Pay Back Period
Another method for evaluating renewable energy technologies and conservation technologies is the calculation of the energy pay back period (EPP). EPP is the time it takes, to save the same amount of fossil (primary) energy as the amount of energy (calculated as fossil energy) used for producing the technology.
Most renewable energy and conservation technologies are paid back within a few years, while their life span is generally longer than 20 years. Especially wind turbines are a good energy investment, as the EPP is only 3-4 months for wind turbines placed at medium-good sites in Denmark, figure 4.6.
1. Energi og ressourcer (Energy and Resources), Niels 1. Meyer and Jorgen S. Norgard. Polyteknisk Forlag, 1989. ISBN 87-502-0675-3.
2. Renere teknologi pa energiomradet (Cleaner Technology in the Energy Sector), Annette Gydesen et al. Physical Laboratory 3, Technical University of Denmark, 1990.
3. Vedvarende energi i Danmark (Renewable Energy in Denmark), Niels I Meyer et al., 1990. ISBN 87-418-5891-3.
Erik Lund, Bakkelandets Energy Office.
The energy offices offer their members a general energy and resource audit of their home. The audit includes electricity, heat, and water consumption, plus recycling of household waste (separation, composting, etc.). It ends up with a report with directions on, how to lower consumption, and which savings can be obtained. This chapter goes briefly through the various elements of an energy audit.
The energy audit roots in the family home, which is the smallest unit of society, but nevertheless a dominating energy consumer viewed as a whole. It is not only possible to save energy, but also to create a better indoor-climate, higher comfort, less building strain - and less strain on environment. The principles of an energy audit are useable for both existing and new buildings, and they should be adopted already in the planning phase to avoid investment mistakes.
Many circumstances play a part when energy consumption is examined: condition of the buildings, and their ability of keeping cold and moisture out, and accumulate heat inside; how the building is fitted out; size compared to number of occupiers; etc. Behaviours of the family play a role too, is everybody prepared to: keep doors shut, turn of the light when the room is not in use, turn off the oven so the after-heat can be used, etc.
An individual family can reduce energy consumption, but there will still be a need for energy supply, e.g. electricity. Therefore it is part of the energy audit to inform about possibilities to get the needed energy with as little environmental impact as possible, e.g. by establishing wind turbine cooperatives. Other elements taken into account are water saving, waste water treatment, and solid waste.
The Energy Audit
The energy audit is a general view based on the total energy consumption and production of a building, and behaviours of the users. The aim must be the smallest possible strain on environment.
When heat loss is reduced to a minimum, then the heat distribution is simplified at the same time, and it can be met by the ventilation system. The less energy consumption, the more dominant is free heat; solar incidence, body heat, and heat from electrical appliances. Therefore the great thing is to accumulate and distribute the free heat.
The building must be tight, as heat loss through joints can be significant. The necessary replacement of air can be provided by a ventilation plant, which transmits the heat from the outgoing air to the incoming air. By doing this, it is at the same time possible to keep an adequate low humidity. Dry air is easier to heat than humid air. The different elements influence each other.
Supply of energy is needed for domestic hot water, heating, light, household appliances, etc. Which source this energy comes from rely on the neighbourhood and local organizing. A local group can manage installation and operation of a wind turbine producing power, or a biogas plant which can produce both heat and power.
The domestic hot water consumption is nearly the same all year round. During the summer period the consumption can be provided by a solar heater. Autumn, winter and spring another heat source is needed for supplement. This can for example be a woodburning stove with integrated hot-water tank, where "waste" heat from water heating can be used for space heating, and distributed to the whole house by the ventilation system.
The following is a short description of the different parts of the energy audit.
Climate Protection, Heat Loss.
The starting point is a low heat loss from the building. This can be achieved by an efficient envelope, that at the outside protects against heat loss, and at the inside accumulates heat. The envelope must be wind tight, but at the same time so light that the cold is not accumulated. The heat loss increases with increasing wind speed, therefore a windbreak belt will also reduce the heat loss.
A greenhouse shelters the building and collects solar heat at the same time. It must be possible to bring me heat from the greenhouse into me house and/or accumulate it. Location of cold rooms in the prevailing wind direction can also protect against wind. Location of windows to the south (east or west) gives a supply from passive solar heating.
When we discuss energy consumption in relation to a home, the consumption from the following must be taken into account:
* production of building materials
* (re-)construction of the house
* maintenance of a comfortable indoor climate
* storage of food, and cooking
* lighting, radio, TV, and various hobbies
* domestic hot water
Each part must be evaluated on the criteria
* minimal environmental impact
* optimum use of materials
By construction and reconstruction, building materials and building methods with limited energy consumption are chosen. Insulation thickness is estimated from the total energy consumption (production and saving).
The house should be organized so that "waste" heat from cooking, laundry, etc., as far as possible becomes part of the heating.
Gunnar Boye Olesen, Copenhagen Environment and Energy Office.
Investments in the energy sector are some of the largest and most long-term investments in the industrialized world. Energy investments are often larger than the total industrial investments in a country, and they have great impact on development of society and environmental pollution. Decisions in the energy sector determine the structure in the far future; e.g. we have to live with power plants for more than 25 years and gas mains for at least 50 years.
Cogeneration in Danish Energy Planning Ole Elmose
The story about how and why cogeneration is part of the Danish energy system, is a good example of how many factors influence the energy planning.
The starting point was some political decisions made in 1978. At that time the Danish Government was a coalition between the Social Demcratic Patty and the Liberal Party, each party with its own special energy political interests. The result was that natural gas should be promoted as desired by the social democrats. But only for heat supply, as the liberals were promised to get nuclear energy for power supply in return. The expected profit from the latter should cover the expected deficit in the natural gas project.
This partition of the energy supply system got into trouble, because of the persistent resistance against nuclear power,; which the Parliament took the consequences of in March 1985: nuclear power was withdrawn from official Danish energy planning.
At tbe same time it became increasingly clear that it would have adverse resource and environmental effects to continue covering the: increasing electricity consumption by centralized (coal-fired) power plants, :as the surplus heat :could not be utilized. The typical annual efficiency of a centralized power plant is about $5% ex plant, add to this a significant:loss in:the grid. This is one of the reasons why the government and the social democrats; signed an agreement in June 1986, stating that there should be established 450 MW decentralized cogeneration in Denmark. Decentralized heat and power (cogeneration) plants have a typical efficiency of 90%. As far as cogeneration is based on natural gas or biomass,::it lead): to a better utilization of the resources, which at the same time has big environmnental infuence.
This development towards decentralization of the electricity supply teas later been followed by new energy political agreements, which show a future energy supply based on cogeneration using natural 8a' and biomass However the adverse effects of the political decision from 1978 appear, as a great part of the heat market is lost for decentralized cogeneration today, because of the individual natural gas supply. Now it appears to be difficult to find enough areas with high enough heat demand to use biomass for cogeneration.
It is important that many groups participate in energy planning, so it is based on the widest range of experience, and that most of us in this field take part in forming our common future.
This section describes some important elements in energy planning. There are of course differences between energy planning at municipal or community level, and national planning. A part of the described planning procedure is the easiest to carry out at national level, but with a good will and a little creativity nearly everything may be implemented locally.
During the last years security of supply, cheapest possible energy supply, and as little environmental pollution as possible have been in focus as the main goals of energy planning. Among other important objectives can be mentioned: furthering employment, and decreasing import. Some energy planners have other goals, e.g. securing the cheapest possible energy supply to industry, protection of capital interests of specific energy companies, or protection of specific markets for energy and energy technology.
Lately the abundant energy supply has caused that security of supply has receded into the background in Western Europe. The main conflicts are now between the desire for cheap energy, environmental considerations, and the interests of the energy utilities. A good energy plan can provide cheaper and at the same time more environmentally compatible energy supply than the present. But all parts of the planning process need political choices, non-political planning does not exist.
The objective of energy planning should not be to provide energy, but energy services. We do not need electricity or gas. We need light, heat in our houses, heat for industrial processes, and so on. This difference is important, as it is often cheaper and less environmentally harmful to increase energy efficiency at demand side (insulate houses, control industrial processes better, etc.), than to invest in the equivalent energy production.
Physical Value of Energy
When energy systems are planned, it is important to keep in mind that different forms of energy have different values. The more other states a form of energy can be converted into without loss, the higher value it has. Electricity and kinetic energy have the highest value, next come gas, oil, coal, biomass, and other fuels, and at the bottom heat. The higher is the temperature of heat, the higher is its value. Wind and hydro power equal kinetic energy, and solar energy equals heat at a very high temperature.
In practice this means that if gas, coal, or biomass are converted into electricity, there will be a good 50% loss, which becomes heat. This heat can be used for residential heating or in industry. Often industrial processes have a surplus of heat at a lower temperature than needed in the process. This heat can be used for residential heating. An essential element in energy planning is to make use of this connection between the different energy forms.
It also influences the energy planning how easy the different types of energy are to transport and store.
Traditional Energy Planning
Traditional Danish energy planning is based on previous development in energy consumption, e.g. 2% or 5% annual growth. For energy sources distributed by grid: electricity, gas, and heat; a state company or another monopoly is made responsible for extension of the systems corresponding to the predicted growth. The company will do this in the way that at first looks most profitable for its administration. Usually they will establish as big and centralized units as possible, and utilize the energy source the company normally uses.
As some older energy planners from traditional energy companies still follow this pattern, traditional energy planning still emerges every now and then. Traditional energy planning makes it hard to utilize saving possibilities. Usually it causes expensive and excessive construction, and it excludes energy sources that the energy company does not manage. All in all it leads to a more expensive and more polluting energy supply system than modern energy planning does.
Modern Energy Planning
Modern energy planning includes:
- the expected development in energy service consumption
- demand-side technologies and their development
- energy resources
- supply technologies and their development, including combined systems, e.g. cogeneration
- drawing up goals of the planning
- an action plan to reach the goals
- evaluation of the plan's impact on environment, economy, etc.
The planning must have a time horizon that at least covers the life span of the energy installations, which means about 25 years. It is an advantage to work with alternative scenarios to compare the effects of different possible developments.
Energy Service Consumption
The cornerstone is an estimation of the existing energy service level, which is based on the knowledge of residential, commercial and industrial space, industrial production, and so on. From this is made one or more forecasts of the development during the coming decades. The forecasts shall be based on expected development, and the human needs that have to be fulfilled. They should not transfer political desire of economical growth directly to growth in energy services.
Nowadays it is cheaper to expand energy systems later on, than to construct large plants at the beginning, therefore it is important not to overestimate the future energy service level.
Energy consuming technologies transform energy into demanded energy services. There are big differences between how efficient this is done, and there are huge possibilities to improve efficiency. There are many options for influencing the efficiency:
- efficiency standards, where demand-side technologies of too low standard are prohibited. It can be standards for apparatus and vehicles, building codes for new constructions and renovation, etc.
- energy labelling, so the consumers can see exactly how energy consuming/efficient the appliances are
- general education about the needs for, and possibilities of saving energy
- subsidies for implementation of energy saving technologies
- grants for development of energy saving technologies
Energy planning must be based on evaluation of the existing demand-side technology efficiency, evaluation of the expected market development without planning, and evaluation of the expenses and savings of different actions that influence demand-side efficiency. These evaluations create a survey of options to influence the energy consumption by energy planning, without affecting the energy service level.
The energy resources in and near the planning area must be estimated. In addition to an estimation of the total potential, it must be estimated which reasonable limits exist for utilization. For example it is reasonable to avoid wind turbines in protected areas, like it is reasonable to avoid uranium mining, mining of low-quality coal, and mining and oil extraction in environmentally vulnerable areas in general.
Together with the evaluation of local resources, a projection of price development for imported energy sources must be made.
The technologies to utilize different energy sources must be evaluated. This both counts for the existing technologies and their distribution, as well as possible improvements, new technologies, and likely development without planning. Supply technologies must utilize the resources as efficient as possible; e.g. heat from power plants and industry must be used for district heating, energy must be transported with as lime loss as possible, and as little as possible.
With supply technology always goes the question, which scale to choose. Pure technical the question can be asked: what is the most effective and cheapest, centralized energy supply with long transmission lines to the consumers or decentralized supply with more local supply units? For a long time the development has headed toward more centralized plants, but during the last decade both economy and efficiency have drastically improved for the smaller units compared to the centralized solutions. In that way the technical arguments for centralized solutions still get less.
Centralized vs. decentralized solutions is not only a question of technology. There is a good part of power concentrated around centralized energy supply systems. Therefore the energy utilities may be interested in centralized solutions, to gain or keep power over the energy systems.
An essential question concerning the energy supply technologies is, how they are owned: public owned, owned by consumers, or commercial. All 3 types can be centrally or decentrally organized ownerships. It is essential for an energy plan that the owners are interested in following the plan, and that they can not hinder parts of the plan through their influence.
There are many ways that the planning can influence owners of energy supply units to follow the desired direction: building licences and other forms of sanctions, competing partnership, information, taxes and subsidies, subsidies for research and development programmes for certain technologies, etc.
Based on the evaluation of development in consumption, and supply options, one or more action plan proposals are made, which meet the aim. As basis and standard of reference the expected development in case of no planning is described (base scenario - business as usual).
Often the plan is made in several steps, where the plan is evaluated on aim and revised for each step. It is then possible to optimize the plan step by step, e.g. aiming at the cheapest energy supply, or achieving certain environmental goals.
An action plan must include a survey of wanted development, and which control mechanisms are needed to achieve it. Often there will also be a physical plan, from which it appears which energy forms are needed in which areas.
The effects on environment, economy, employment, etc., must be calculated to assess the action plans. Economic effects ought to be calculated in total as socio-economic effects, thus including environmental costs and other external costs. Furthermore economic consequences must be calculated for different consumers, energy utilities, state, municipality, and balance of payments. A socio-economically and environmentally reasonable plan may be a strain for a group of low-income consumers. In this case it is better to carry out the plan and compensate the consumers, than to continue to have an expensive and polluting energy system. Consumers compensation, e.g. partly repayment of heating bill, can in itself be formulated in a way that stimulates energy conservation and use of renewable energy.
Integrated Resource Planning
In USA some states have introduced an efficient, modern planning method, primarily in the electricity sector. It is integrated resource planning (IRP), also called least cost planning (LCP).
The method is to set up all possibilities for supply, and for control and rationalization of consumption (demand-side management, DSM), and then choose the socio-economically cheapest solutions. In USA the system works in a system with private power utilities having monopoly in certain areas. On the other hand the utilities are controlled by Public Utility Commissions (PUC).
The method has already led to considerable savings in e.g. California, and a study forecasts that it will reduce USA's electricity consumption 20% by the year 2010.
Integrated resource planning is based on three fundamental principles:
- utilities have to make total investigations frequently, of all options to cover the consumers' demand for energy services
- reduction of the energy demand by increasing energy efficiency is an important economical alternative to electricity production
- all advantages and disadvantages according to supply and conservation options must be estimated, to find the combination which is best for all the involved parties: utility, consumers and society.
There are 6 critical elements involved to succeed with integrated resource planning:
1) There must be a controlling authority, which has strength and will to introduce IRP, and guarantee fulfilment of the plans. It must ensure public participation in the utilities planning. The authority has three main tasks: to make sure the utilities make the plans, to set guidelines for and evaluate the plans, and to establish controlling mechanisms which secure that the utilities fulfil the plans.
2) The next critical issue is the IRPs themselves. Normally they consist of at least: an electricity demand forecast, a survey of possible increase in efficiency to reduce future demand, an examination of possible import from other utilities, selection of an optimal combination of supply and efficiency measures, and an action plan on how to reach the optimal system. It is the utilities who make the plans within the conditions given by authorities.
3) To enable the utilities to find the optimal combination of supply and efficiency options, it is needed to compare these very different options. A third critical element is therefore that there must be clearly defined directives for comparison of savings and costs connected to supply and increasing efficiency. Usually efficiency costs are calculated as costs related to marketing, supply, and installation of the energy saving device. The savings are calculated as costs saved by the utilities when they distribute less electricity. Here must be included both short-term savings like saved fuel, and long-term savings like saved investments in new power plants.
4) The fourth critical element is employ of competition to select, evaluate, and use resources from independent companies. Invitations for tenders enable the utilities to let the market forces act, and choose the cheapest supplier of power or efficiency. The invitations were originally reserved for independent power production based on renewable energy and cogeneration. Now the method also includes traditional power production and energy savings.
5) The fifth critical element is control of the power sector, to guarantee the utilities profit from investing in efficiency instead of new power plants. The utilities may be allowed to profit from investing in efficiency according to the yield they get by supplying, or they may be allowed to get a higher rate of profit. This is practically done by letting the power utilities incorporate expenses and profit relating to energy efficiency measures in the electricity price. This gives a slightly higher electricity price, but will in total profit the consumers.
6) Environmental costs must be included in the calculations. It is difficult to price environment, but the only price that for sure is wrong is 0. Therefore it is better to set a price on uncertain background, than setting no price. A recent estimation from USA puts environmental costs for power produced at coal-fired power plants with desulphurification at 5 cents/kWh, and nuclear power at 3 cents/kWh.
Savings due to integrated resource planning are largest in an electricity system without overcapacity. In this case there is a direct choice between savings and construction of new power plants. The method also leads to savings in systems with overcapacity, compared to traditional energy planning.
The Role of Popular Organizations
In some states in the USA, independent organizations have the possibility to take part in the integrated resource planning. Part of this work is payed by the utility. This agreement is made to give the consumers an independent assessment; it is after all the consumers who via the electricity bills pay for the utilities planning.
In Denmark it has not been possible for the grassroots organizations to get the same directly influence on the power utilities planning. On the other hand popular environment and energy offices have succeeded in getting an officially recognized role in implementing the national energy plan. The energy offices manage dissemination of information targeted at consumers and private initiators of renewable energy. Activation of these groups is a condition of changing to renewable energy in a free market economy.
1. Energy Action Plan 2000. The Danish Energy Agency, Copenhagen 1990.
2. Handbog i lokal energiplanlogning (Handbook in local Energy Planning), OVE's forlag, Copenhagen 1986.
3. Energihandlingsplan 90 (Energy Action Plan 90). Frede Hvelplund, Hans Bjerregaard and Karl Emil Seerup, AUC's forlag, Aalborg 1989.
4. Alternativ E;nergiplan 83 (Alternative Energy Plan 83). Niels 1. Meyer, Frede Hvelplund et.al. 1983.
5. Integrated Resource Planning in E;urope, Association for the Conservation of Energy, London 1992.
Gunnar Boye Olesen, Copenhagen Environment and Energy Office
The transport sector is the sector with the fastest growth in environmental pollution, e.g. CO2-emission. While the official Danish energy plan, Energy Action Plan, 2000, expects decreasing energy consumption and less pollution, then the official transport action plan expects increasing energy consumption for transport and increasing emission of some pollutants /1/.
Options in the Cities
The worst local environmental problems due to traffic exist in the cities. Here at least 80% of air pollution at street level comes from traffic pollution, and nearly half of the dwellings are bothered by noise. Also in the cities there are most options to reduce the harmful traffic effects.
Most important is to move passengers from cars to public transport and bikes. If public transport is faster and cheaper than motoring, then most people choose public transport. Improvements in public transport are, e.g. additional and faster rail lines and buses, as far as possible with separate bus lanes. Improvements for bikers include bike lanes at all busyroads, and bike routes through the cities. Motoring in cities can be made more expensive by parking toll, and toll on driving into or through city areas. This kind of taxation does not make it more expensive to drive cars outside cities, where good public transport systems do not exist.
Urban planning is another important element in reducing harmful effects due to city transport. The planning must reduce the transport demand as much as possible, and allow everybody to use public transport and bikes.
The plans must ensure that it is possible for everybody to live in biking distance form their job. Dwellings must be placed within biking distance from a station, and large shopping centres and workplaces within walking distance.
A number of other things effect traffic, e.g. abolition of transport deduction would make it more attractive to live close to ones job, and thereby pollute less.
Copenhagen Environment and Energy Office has together with a number of environmental and traffic organizations made a traffic action plan for Copenhagen following the guidelines above /3/. By following the plan, pollution and energy consumption from traffic can be halved in 10 years, and at the same time more space is provided on existing roads in Copenhagen. More road space is due to the fact that bus passengers take up much less space than private car drivers.
It is interesting that it is possible to reduce environmental impact from traffic that much, just by changing the price relation between individual and public transport, and invest the profit in public transport. Unfortunately the proposal has run into strong opposition from the car and asphalt business that feel their markets threatened; from the highways directorate which is against spending tax revenue from motoring on public transport; and from FDM, that is against any new tax on cars whatever the effects are. As long as these circles has the power that kind of proposals will barely come through.
Options for Longer Distances
For long-distance passenger transport trains must be given higher priority than cars and planes, if there is a wish to reduce environmental pollution. Like in the cities, price, speed, and comfort are decisive, when choosing means of transport. Furthermore there must not be long waits when changing trains, and there must be connection between long-distance and local traffic. Especially international train transport needs to be improved. Today there are good possibilities to make fast trains competitive to cars and planes on distances shorter than 500 km.
Besides it shall be considered to halt growth in transport. E.g. an environmental tax could be introduced on holiday trips, with tax-rate related to travel distance.
About goods higher priority must be given to train and ship, than to lorry and plane. Also goods transport is chosen by price and speed, plus guaranteed delivery in time. At rail it is about introducing more efficient goods transport, e.g. by reducing the time consuming shunt switching, and establishing terminals where goods can be reloaded quickly between road and rail.
It is important that lorries pay for their real environmental costs and road wear; today they only pay part of the expenses. Part of the expected growth in environmental pollution from traffic, is due to foreseen increased goods transport, e.g. caused by the EC internal market. But we would not get this growth in goods at all, if the transport price raised, e.g. to the real price inclusive environmental costs. Then local production will be more profitable than long-distance transport.
Unfortunately the above mentioned car lobby until now succeeded in having higher priority given to motorways and bridges, than to public transport. The majority of the Danish population is against highways and bridges financed by taxpayers money and on their risk. But as long as this majority is not willing to indicate their standpoint stronger than now, we are not likely to see changes in the traffic situation.
Options in the Country
In the country, where people are living more dispersed, a more flexible public transport system is needed, e.g. with tale-buses that only run when there is a demand. There should also be used smaller and more energy efficient buses. It is important to keep a basic public transport service, which makes it possible to travel without having a car.
There will be some areas where people can not do without cars. It is therefore important that people can use cars in the country, and then shift to public transport in cities, and when they travel over longer distances. There must be good possibilities for changing between cars and public transport, for example by driving to the nearest station, park the car, and continue by public transport.
Together with the general solutions there arc a number of possibilities for active citizens to make their own local area less pestered by traffic. Roads can be turned into calm roads (max 30 km/h), play-stay roads (max 15 km/h), or pedestrian/bike/ bus roads. Road area can also be seized for parking, or other more useful purposes.
In some municipalities active citizens have good chances to get subsidies from the municipality for traffic improvements, if they have secured wide local support for their suggestions. In this time of privatization it will in some cases be necessary that the landowners take over the road, to have the changes. In this way they also get responsibility for the future maintenance. For example the municipality can pay part of the expenses for the change.
These local solutions can be made without an environmentally vulnerable general traffic plan, but it will be more difficult, amongst other because of lack of space due to many cars.
There are a number of possibilities of introducing more efficient vehicles, both in public transport, and for the remaining car transport. These can be promoted by taxes which favour the most efficient vehicles, by efficiency standards, and by inspection of older vehicles, so they do not get more petrol drinking during time.
It is also possible to use more renewable energy in the transport sector. In public transport electricity can be used for trains and trolley buses. Cars can run on bio fuels, or be substituted by electric cars. Though electric cars have a low efficiency, due to the heavy batteries that have to be carried, and their 10-15% loss. Tax exemption of bio fuels can help.
A new Transport Policy is Needed
As mentioned, a totally new transport policy is needed, if we want to solve the environmental problems related to transport. Today there is a row of obstacles to get a reduction of environmental pollution in the transport sector.
In the following some of the barriers and solutions suggested by OVE are mentioned /4/:
* in cities private cars have been favoured above more resource efficient trains, light-rails, and bikes. Future investments in the transport sector ought to be spent on constructing faster rails and light-rails, and improving safety for bikers.
* bus and train fares, tax systems, and toll on driving and parking cars, shall make rails, light-rails, and buses more economic favourable than private cars.
* flying has been favoured above trains. By investing in high-speed trains, transport by train can get a comeback. High-speed trains must be energy efficient, and must not have severe environmental impact.
* while motorists normally have a strong lobby organization, then public transport passengers normally have no or only a weak organization. Popular organizations and public transport companies should encourage public transport passengers to organize themselves.
* urban planning often neglects consumption of resources connected to commuting and other necessary city traffic. Urban planning should favour shortest possible commuting, and ensure that as many as possible are able to use public transport.
1. Trafikhandlingsplanen (Traffic Action Plan). Danish Ministry of Transport, 1990.
2. Energi- og Trafikplanlogning (Energy and Transport Planning), Kaj Jorgensen. Physical Laboratory 3, Technical University of Denmark, 1991.
3. Bedre Bytrafik (Improved City Traffic). Published by Trafik- og Miljosamarbejdet i Kobenhavn (Traffic and Environment Coalition in Copenhagen), 1989.
4. OVE's handlingsplan for Vedvarende Energi i Danmark (OVE's Action Plan on Renewable Energy in Denmark), 1992.
5. E;F's Gronbog for trafik (EC Green Book on Traffic). The EC-Commission 1992.
1. Danish Motoring Association
We don't need all the energy we consume today. Considerable energy savings can be achieved both in households and the commercial sector, if we use the most efficient energy technologies existing today and change our consumer behaviours. The more energy we save, the easier it will be to cover the remaining consumption by renewable sources.
Ann Vikkelso, Copenhagen Environment and Energy Office
The energy crisis in 1973 brought the domestic energy consumption into focus in Denmark. As an immediate initiative energy saving campaigns were carried out to influence people's user habits. In longer term the requirements on energy consumption in new buildings have been intensified, more energy efficient devices have been developed, and work on designing low energy buildings has been done.
The individual consumer has great influence on the size of energy consumption in the house, partly by virtue to our consumer behaviour, partly as a result of the devices we choose to use.
When working on increasing domestic energy consumption, it is important to look at the total energy consumption of the house, related to different initiatives. For example installation of mechanical ventilation with heat recovery causes a fall in heat consumption, but at the same time extra consumption of electricity is introduced, and it is produced at lower efficiency than the heat (unless there is electric heating). Likewise replacement with more efficient electrical devices will cause a fall in free heat supplement. Some people use this as an argument against increasing electricity efficiency, but often the reality is that the heat cannot be used, and electricity is an inefficient heat source (at coal-fired power plants the efficiency is only 30-40%).
Low Energy Building
The house functions as a climate shelter, which we use to maintain a comfortable climate for ourselves, regardless of the surrounding nature's behaviour. Sometimes it is too hot, other times it is too cold. The natural conditions that have an influence on energy consumption related to heating or cooling are temperature, humidity, wind speed, and solar irradiation. In our northern climate it is mainly a problem to maintain a convenient temperature during the winter.
2/3 of a buildings heat loss is a transmission loss and l/3 is a ventilation loss. The transmission loss depends on surface area of the building, insulation standard, temperature difference between outside and inside, and forced cooling because of wind.
An important principle of low energy building is adaption to the surrounding nature. This means to close to climatic liabilities and open to the assets. For example wind is an asset on hot summer days, but a liability during winter. As the climate differs on different localities, it is important to make clear which criteria must be given a high priority, in design. Often we can get inspired by traditional local building, which has evolved through many years experience with the actual climate.
To be characterized as a low energy building in Denmark, it is pure technically required that the buildings heat consumption does not exceed 50% of the consumption of a building complying with the building code. Danish Institute of Technology sets up 10 very concrete instructions to be followed for low energy building 11/:
1. Choose simple solutions.
2. Place only windows, where positive heat balance can be achieved.
3. See to efficient insulation without thermal bridges.
4. Consider tightness and fresh air supply.
5. Build glass rooms that decrease surface area of the building.
6. Locate living rooms at the sunny side.
7. See to efficient regulation of central heating installations.
8. Use solar heaters and solar walls as solar heat contribution.
9. Minimize electricity consumption by choosing high efficient electric devices.
10. Use materials with low energy consumption for manufacturing and transport.
Utilization of active and passive solar heating is treated in the chapter on solar energy.
Homes should be built compact and well-insulated. The energy consumption is very dependent on the surface area and shape of the building. For example a roof with high pitch deflects the wind, and reduce the effect of the cold winter winds.
Multi-family homes have a lower energy consumption per mÃ¬ than single-family homes. Figure 7.2 shows the effect of better insulation and compact building.
An interesting development is organic shaped houses, which fit into the surrounding nature, and at the same time take advantage of the ground shape for shelter, etc.
Location of the Building
The building should be oriented so that it makes the best possible use of the sun. During winter the sun can provide a significant supplement heating of the home through large south facing windows. To have full benefit of passive solar heating, building materials with big thermal mass are used, e.g. concrete, masonry, and stone. In that way the daytime sunshine can be utilized in the evening (day-to-night storage). At the same time a big thermal mass reduces diurnal temperature shifts, as well as problems with overheating during summer will be less.
Windows should be vertical, because they are self-regulating that way, as the sun stands higher above the horizon during summer than during winter.
Overheating during summer can also be met by for example overhangs or window shades. Likewise. shading plants can minimize summer heat gain. For this purpose deciduous trees should be chosen, so they shade as little as possible during the winter season.
The building should be sheltered from cold winds especially during winter. In Denmark the predominant wind directions are north and west. If the ground is south sloping, the house can be built into the slope. Soil is a good insulator, and the hill functions as a windbreak. There can also be build banks of earth at the northern side of the house. Another option is to establish wind breaking banks close to the house, or plant evergreen trees as wind mantle. Also a fence, garages, and sheds function as windbreaks.
The home should be organized with primary living rooms (sitting room, kitchen-dining room) to the south, where the sun provides light and heat. This way they are also placed farthest away from the cold winter winds. In the centre or to the north are located the secondary living rooms (bedrooms), that are only heated occasionally. Non-living rooms like scullery, workshop and garage are located to the north. This way they are insulating the heated part of the house.
Chimneys from heating installations should be located in the centre of the house, to utilize heat from the smoke as good as possible. A chimney along the outer wall is to heat for the birds.
There should be a windbreak or weather porch at the entrance to reduce heat loss. The entrance can profitably be placed lower than living rooms, as the cold air stays down.
The dome is one example of ecological and energy conscious building. The dome is an almost ball-shaped house made of triangular elements.
The advantage of the dome is that it is simple. And it only takes a small consumption of materials to build a stable and strong envelope without pillars and interior walls. The ball-shape implies that the total surface is smaller compared to an ordinary house of equal size. The round shape of the dome also implies that it is less sensitive to wind, which furthermore improves the energy economy. The dome is more difficult to furnish than ordinary houses, but creative persons will probably rather find it an exciting challenge than a drawback.
Villa VISION is an idea of the future home, where the architects behind have "tried to reach a new balance between nature, house, and residents" !1/. Until now the house has been shown as full-scale model at an indoor exhibition, but in the 90'ties it will be built at a site close to Copenhagen.
The idea is, that the house itself will produce the energy demand, so it is independent of fossil fuels. At the same time the ideal is, that the residents are in balance with the rhythm of the day. The house's floor plan is round, with an eastern room oriented in the direction where the sun rises at midsummer, and the western room in the direction where it goes down. Towards south is located a room with front and roof covered by photovoltaics for electricity production. These rooms are the family's bedrooms. The areas towards south-east and south-west, between the three rooms, are glazed-in patios that help lowering heat consumption, as they reduce the outer surface of the house. The living room is located in the centre. The roof of the living room slopes towards south, and solar collectors for hot water production are placed on it. To the north are the kitchen and a hall. The northern outer walls are covered with soil up to the windows.
The house will be extremely well-insulated with 40 cm mineral wool, and the newest and most energy efficient technologies in all fields are utilized. The patios will have charcoal-gray floors, walls, and pillars, to absorb as much heat as possible, and give it off again during the evening. The glass cover will be made of vacuum glass with silica-aerogel, which is 5 times more efficient than sealed glass units. Water saving devices will be installed everywhere in the house, the kitchen will be equipped with a waste separation system, and it is planned to clean and recycle the waste water locally.
The intention is, to equip the house with as much automatic control of energy consumption as possible, to eliminate bad user behaviour. Control systems for heating, light, ventilation, opening of windows, etc., will be utilized.
Villa VISION is a very hi-tech idea of tomorrow's home. There are many other possibilities for reducing energy consumption at home, where we still control our everyday life - and we consider our actions ourselves. But anyway, I think, Villa VISION gives some interesting ideas for alternative building organization and design.
Huge savings can be obtained by insulating old houses, and it must be a matter of course to construct new houses with efficient insulation.
It is however not only insulation depth that counts. Also hot water consumption, ventilation loss, regulation, and user behaviour influence the total heat consumption. For each degree the temperature is lowered about 6% of the energy consumption is saved. 20›C is sufficient in living rooms, and unused rooms should not be heated.
All radiators should be thermostatically controlled, to ensure a comfortable, but not too high temperature. At the same time can perhaps be installed clock-timers that turn off the circulation pump at night, or automaticalIy lowering of night temperature. However, the latter is unnecessary, if one remembers to turn off the heat.
Blocks of flats and other homes with collective heat supply ought to have individual metering of the heat consumption, as it encourage energy savings.
Insulation of Existing Buildings
The heat consumption is often large in older buildings that are poorly insulated and uptight. Afterinsulation will under most circumstances give a higher comfort in addition to lower energy consumption. Problems with draught are rectified, partly because the building often gets tighter, partly because the inner walls get warmer. When draught is avoided, it is possible to lower the room temperature, and at the same time keep up the comfort level, in this way extra energy is saved.
It is substantial that the insulation is made carefully. All edges must be cut precisely. A damp course is placed at the warm side of the insulation, to hinder damp in passing through the building layers and condense at the cold side with the risk of causing damp damage. It is also important to ensure that all water pipes are at the warm side of the envelope, also after insulation. Otherwise the loss from hot-water pipes will be unnecessarily large, as well as there is a risk of bursting a water pipe that can freeze.
Cavity walls can be insulated by blowing insulation material into the cavity between the outer and the inner wall. This is done from the outside. Today the following materials are used for cavity wall insulation in Denmark: granulated mineral wool, granulated paper, polystyrene balls and granulate, expanded volcanic stone material, plus PUR-foam and FU-foam.
Solid walls can be insulated either at the inside or at the outside. The two methods have different benefits and disadvantages. Outside insulation covers the total wall surface including horizontal divisions, by which thermal bridges are avoided. On the other hand is the front is totally changed.
Outside insulation is often more expensive than inside, but it is profitable if the front is going to be renovated anyway. It is easier to insulate at the inside, and it can be done as going along. On the other hand, it is a disadvantage in small flats that the already small living space gets even smaller, when insulating at the inside.
Ceiling and Loft
The insulation thickness at lofts should at least be 200 mm, and all parts of the construction with surface to the open air must be insulated. It will often be smart to insulate flat roofs at the outside. At the same time it is possible to establish a sloping roof. A
Floors over crawl space or unheated cellars are often easiest to insulate from below, by putting up insulation plates between beams. The simplest way to insulate floors directly on the ground (terrain floor) in houses without cellar, is vertical insulation of the plinth and foundations. Terrain floors can also be insulated with SO mm of mineral wool at the top of an existing concrete floor.
A great share of the house's heat loss is through the windows. The heat loss can be reduced by replacing the old windows with sealed units, or even better heat mirror windows. Heat mirror windows insulate nearly twice as good as ordinary sealed units with air-filling.
The improved insulation is achieved by coating the glass with a special coating that lets most of the light and solar radiation pass through, but holds back the heat radiation from inside the house. New types of windows with even higher heat resistance are being developed, as already mentioned.
Heat loss through windows can also be reduced by setting up interior windows when having single layer windows or sealed units. A single layer window in combination with an interior window insulates just as well as an ordinary sealed unit, and it is cheaper. Further improvement can be achieved by establishing shutters that are closed at night. There exist various types, also some that can be handled from the inside. Likewise, use of heavy curtains during winter, or tight-fitting roller blinds that causes stationary air, can reduce the heat loss.
Around one fourth of domestic energy consumption is spent on water heating. The energy consumption can be lowered by
- reduction of hot-water consumption
- regulation of temperature
- economical water heating during summer
- lagging of tubes and tanks
- stop of hot-water circulation
- maintenance of the installation
Water savings can be achieved by changing behaviour, by using various water saving devices, and of course by taking care that the water installations in the house are tight. If a household saves 50 litres of hot water a day, it matches an annual energy saving of 100 litres of oil.
Many water installations have an unnecessary high water consumption. Old water taps and showers often have a maximum flow of 15-20 litres per minute. Low-flow fittings, that ensure a maximum water flow of 6 or 8 litres per minute, can be mounted at all taps and showers, and will often be payed back in a few months /81.
When the maximum water flow is reduced, there should at the same time be mounted aerators at the tapping places. These yield an airy jet of water, and therewith a bigger rinsing effect, also when the water flow is low. Likewise exist showers especially developed to function well at low water flow.
In connection to showers can also be installed a shower-stop that shuts off 90% of the water. As the water is not shut totally off the water temperature is kept. So if the shower-stop is closed during soaping, one avoids wasting hot water to regulate the temperature, when the water is turned on again.
If new taps are installed, it is a good idea to choose single-handle taps, and preferably thermostatically controlled for the shower. A thermostatically controlled mixer tap functions as the shower-stop. Single-handle taps are easier and faster to regulate than two-handle taps, so less water is wasted.
Good user behaviours:
* Take short showers instead of tubs.
A tub consumes 100-150 litres of hot water, while a low-flow shower only uses 8 1/min.
* Shut off the water, while soaping and shampooing.
* Take cold showers, it is healthy and refreshing.
* Don't let the tap run unnecessarily.
* Don't wash dishes under running water, use a bowl instead.
* Use cold water to rinse dirty service.
From 1972 to 1987 the total gross energy consumption has not changed in Denmark, while the electricity consumption has increased. Efficiency of the individual electric device has improved during the same period, so the increased consumption is due to more electrical appliances than before.
The large electricity consumers in the household are lighting, laundry, cooling, and cooking. Higher consumption is introduced, because we get more and more electrical appliances. Nearly all Danish households have a refrigerator, a freezer, a washing machine, and a TV-set. But also tumbler driers, computers, dishwashers, etc., get more and more common.
The total electricity consumption is a product of electrical device efficiency, number of appliances, and the time they are used.
There are large technical possibilities for rational use of electricity. New efficient devices on the market consume considerably less electricity than older models. By utilizing the technical potential of savings, it is possible to save 2/3 of the electricity consumption in Denmark /6/. When replacing old appliances, the electricity consumption ought to be examined carefully, as the most energy consuming appliances consume up to 3 times as much electricity as the most efficient on the market, figure 7.20.
It is important to work on regular labelling of electrical appliances, so the consumers have a chance to compare the different products when shopping. In Denmark it is fixed by law that all ovens shall be labelled with energy consumption. Unfortunately it is not all manufactures who respect this. On the other hand one can get help from the Consumers Agency that tests white goods. The test evaluates both consumption and quality. Likewise the power utilities have established a database with information on electricity consumption for a wide range of refrigerators, freezers, washing machines, and dishwashers. Part of the information is published in free brochures /11/, and one can phone the local power utility to get information on specific devices.
There are further savings to be achieved by correct use of the electrical appliances, as well as it is necessary to consider, if we need all these electrical devices at all. The energy service dry clothes can easily be obtained without using a tumbler, thus without consuming electricity.
The most common source of light in homes is the incandescent lamp, and in some places the more efficient fluorescent tubes. But during the last years low energy light bulbs (CFL, Compact Fluorescent Lamps) have been developed. In principle CELs work the same way as fluorescent tubes, but they fit in an ordinary holder. In contradiction to fluorescent tubes, electronic low energy light bulbs can stand being turned on and off again and again, without reducing the life span.
An 11 W low energy light bulb delivers just as much light as a 60 W incandescent lamp, and it lasts for 8000 hours, whereas the durability of an incandescent lamp is only 1000 hours. The low energy light bulb is more expensive than ordinary light bulbs. It costs appr. 130 DKK, compared with 8 DKK for an incandescent lamp. In Denmark this is amply compensated by saved electricity. As the electricity price is 1 DKK/kWh the profit will be:
(60-11) £ 0.00lkW £ 8000h £ 1DKK/kWh + 10 £ 8DKK + 130DKK = 340 DKK
Especially at places lightened many hours every day, the lamps should be replaced with low energy light bulbs. This provides both the largest energy saving and the shortest pay-back period.
10 pieces of good advice on lighting
1.Use energy saving light bulbs, where it is possible (be aware of the reproduction of colours).
2.Use high efficient holders, when possible (needed screening shall be met).
3.Choose lamps that do not get dirty quickly, and are easy to clean.
4.Choose electric components that meet the standards.
5.Use individual light from work lamps, where it is possible, instead of large general lighting. The light quality has to be satisfactory.
6.Divide the lighting system into sections, which can be operated individually. Plan the lighting in details to ensure flexibility.
7.Turn off unnecessary light either manually or automatically, e.g. by a timer.
8.Utilize natural daylight (take care of heat and blinding problems).
9.Choose light colours for the room surfaces, hereby as much light as possible is reflected.
10. Introduce systematic maintenance of lighting.
More than 10% of the Danish electricity consumption is spent on storage of food in refrigerators and freezers. By utilizing the most efficient refrigerators and freezers on the market, this consumption can be reduced to 25% of the consumption related to old models.
LER200 is a 200 litres low energy refrigerator developed at Physical Laboratory 3, Technical University of Denmark, which consumes less than half of the energy other refrigerators of the same size consume. The saving is obtained by doubling the insulation thickness, and increasing efficiency of the cooling system. If an old refrigerator is replaced by a LER200 more than 300 kWh electricity is saved per year.
Proper placing, maintenance, and use of refrigerator and freezer:
* Place refrigerator/freezer so there are space around condenser and ventilation grating. If the refrigerator is build in, there must be 10-15 cm space over me fridge and a small crack at the bottom.
* Place possibly the refrigerator in a colder room (larder, scullery). Place the freezer cold (cellar, outhouse).
* Do not place the refrigerator close to a radiator, cooker, or other heat source.
* Keep condenser clean. Dust insulates and increases the electricity consumption.
* Examine the tightening strip. It must be whole, and the door must close tight. It can be controlled that the door closes tight, by trying if a paper strip is stuck all way round the door.
* Keep a temperature of 5›C in the refrigerator and +18›C in the freezer, it is cold enough. Control the temperature with a thermometer.
* Defrost the fridge frequently, if it hasn't automatic defrosting. The frost layer must not exceed 1/2cm
* Thaw out frozen food in the refrigerator. The cold from 1 kg frozen meat corresponds to at least one hour's electricity consumption.
* Cool down warm food before it is put in the refrigerator/freezer.
* Do not open the refrigerator or freezer more often than needed, and don't keep it open for a longer period.
Electricity is a poor energy source for cooking actually many cooks prefer gas. Gas is also better from an energy point of view. The efficiency of an electrical cooker and a gas cooker is more or less the same, namely about 50%. But as electricity mainly is produced at coal-fired power plants with an efficiency under 40%, the real efficiency of an electrical cooker is only 20%.
The electricity consumption, and at the same time primary energy consumption can therefore be lowered by shifting to gas. And at least replacement of gas with electricity, should be stopped in areas where gas is supplied. Another possibility is to boil water in an electrical kettle, where the heating element is built-in, this way the heat loss decreases significantly. Likewise there are great potentials for electricity saving, by utilizing electrical pots with a heating element built-in at the bottom, good heat distribution, and efficient insulation of the pot. But this is a field, where the development has only just begun.
The microwave oven has been proclaimed as a great energy saver by many, especially when cooking small portions, and when "boiling" vegetables. But a mini oven doesn't consume more energy than a microwave oven, and- neither do vegetables steamed in small amounts of water, in a pot with a tight lid. On the contrary a microwave oven often introduces bad user habits, where food is taken directly from the freezer, and thawed/cooked in the microwave oven.
Energy conscious cooking:
* Use even pots. A pot with an uneven bottom consumes up to 50% more electricity.
* Use pots that fit the size of the hotplate. The pot must cover the whole plate.
* Regulate the hotplate properly. Step-regulated plates are set at the highest level until the food is boiling, then it is fumed down as much as possible.
* Remember always to put a tight lid on the pot.
* Cook with little water. A few decilitres of water is enough to cook potatoes and vegetables. It saves up to 30% electricity, and the vegetables keeps taste and nutrients better. Egg can be boiled with only a few teaspoons of water, and the plate can be turned of, as soon as the water is boiling.
* Do not cook frozen food (it ought to be thawed out in the refrigerator)
* Utilize the afterheat. Turn of hot-plates and the oven 5-10 minutes before the food is ready.
* Put the food in a cold oven.
* Fill the oven, different meals can easily be prepared at the same time.
* Poor the coffee into a vacuum jug, instead of keeping it warm at the coffee brewer.
* Don't let the cooker hood run on higher level than needed.
* Keep the cooker hood clean. Rinse the filter once a month.
Considerable amounts of energy for laundry can be saved. In average one fifth of the electricity consumption in households is used for washing clothes. Technical improvements of washing machines have been achieved, so the most efficient washing machines at the market today consume only 50-60% of the electricity amount consumed by older models.
There are also great saving potentials related to good user behaviour:
* Fill the washing machine every time. Invest in a few extra socks and underwear, so it is unnecessary to wash with a half-full machine.
* Skip the prewash, when it isn't needed. It saves 20% electricity.
* Do not wash at higher temperature than needed, wash at 60›C instead of 90›C saves 30% electricity, and it also wears the clothes less.
* Use of tumbler drier is needless. The tumbler is a significant energy consumer, and wears the clothes.
* Do only wash dirty clothes. There is no need for changing a l-shirt several times a day.
The heating installation
A good part of electricity used for running the heating installation can be saved. In central heating systems the circulation pump can be turned off, when there is no heat consumption. This can be done manually, or by mounting a thermostat or a clock timer at the pump. If there is an electrical water heater, this can also be regulated by a clock timer.
1.Huset som solur (The House as a Sundial), Flemming Skude. Energistyring no. 3, November 1991.
2.Syv med et sm'k (Seven in One), Ove Morck and Peder Vejsig.
3.Retningslinier for konstruktion med sigte pa passiv solopvarmning (Guidelines for Construction aiming at Passive Solar Heating). The EC-Commission, DG XII, 1980.
4.Regional Guidelines for Building Passive Energy Conserving Homes. AIA Research Corporation, Washington DC. 1978.
5.Isoler nu (Insulate Now), SBI-anvisning nr 100.
6.Energi & Ressourcer - for en b'redygtig fremtid (Energy & Resources - for a sustainable future), Niels 1. Meyer and Jorgen S. Norgard. Polyteknisk Forlag, 1989. ISBN 87- 502-0675-3.
8.Vandsparebogen (The Water Saving Handbook), Ann Vikkelso. OVE's Forlag, 1992. ISBN 87- 87660-687.
9.Elbesparelser i Danmark (Electricity Conservation in Denmark), Gunnar Gjelstrup et.al. AKF, 1989. ISBN 87-7509-211-5.
10. Brug el med omtanke (Use Electricity with Care). Danske Elv'rkers Forening.
11. Energisparepile - kort er goat (Energy Saving Arrows - short is good), Danske Elv'rkers Forening.
12. Energistyringshandbogen (The Energy Management Handbook). Energi-Spareudvalget & Foreningen for Energistyring. 1990. ISBN 87-983525-0-4.
Jan Viegand, Copenhagen Environment and Energy Office.
The commercial sector is harder to cover for the energy offices compared to private homes. It needs more technical knowledge, and expensive measuring instruments are in general required. It is also natural for a company to make use of a consulting engineering company or the power utility, if the company wants to do something on its energy consumption.
Furthermore the energy adviser must have a licence from the Danish Energy Agency, to be permitted to carry out energy audits that qualify for repayment of CO2-tax. And for many companies the possible repayment will be the motive for having an energy audit done.
But the energy office can take part as initiator targeting all local companies. The knowledge of neighbouring companies, combined with a basic knowledge on conservation potentials, can make the companies decide to have an energy audit.
In addition many energy advisers have sufficient knowledge to advise offices, shops, and small-scale companies on possible energy savings from light, heat, ventilation, office machines, and small refrigerating plants.
The contact to the company ought to happen at the highest possible level. If activities are initiated at the lower level, the management may restrain them. The opposite is very seldom the case.
Company Character and Economy
The energy use is very dependent on the character of the company. Typically the demands are
- Offices: Light, heat, office machines, ventilation.
- Shops Light, heat, ventilation, and cold counters in foods shops
- Utilities: Pumps
- Industry: Light, heat, engines, pumps, ventilation, refrigeration, compressed air, process heating.
- Agriculture, gardening, and forestry: Work tools, light, heat, motors' ventilation, pumps.
The companies can be using electricity, heat, and the fuels natural gas, gas oil, fuel oil, coal, and biomass.
Most companies can get the energy tax and VAT on purchased energy repaid. However the companies pay half of the CO2-tax from January 1993, unless the energy consumption is very big. The real energy price for the companies can be half as big as the private consumers' energy price.
The low energy price gives the conservation measures a longer pay back period. And into the bargain the companies usually make severe demands on the pay back period: Over three to four years are seldom accepted.
Even if the rentability of a conservation measure is acceptable, there is a high risk that it will not be implemented. The main aim of a company is to produce goods or deliver services, and the resources of the company in terms of staff and capital are therefore reserved for these purposes. The energy consumption has low priority.
The arguments for energy savings targeting the company are:
- The installations usually work more reliable, after the energy saving measure is carried through.
- It can give a better image of the company towards both staff members and customers, that the production is efficient without waste of energy and other resources.
- High rentability
Working reliability is often the best argument, because production stops as a rule are expensive.
The Energy Audit
An energy audit consists in giving the company proposals for energy savings and their rentability. This can be done at many levels, ranging from a quick examination of the company, and a talk with the staff, to a thorough analysis during several weeks' and use of meters The accuracy of the measures rely of course on the time spent. It depends on the consumption size, how much time it is allowed to use on the energy audit.
The energy audit consists of:
- Specification of energy consumption divided on energy sources and use.
- Evaluation of conservation potential, based on estimation of the company's devices and comparison of energy key-figures with similar companies.
- Calculation of the theoretical consumption based on the energy demand.
- Posing of conservation measures - and their economy.
- Reporting to the company and follow-up.
The company seldom knows how much energy is spent on each device. The first important step therefore is to estimate a division of consumption on use. For example how much energy is used for light, ventilation, air compressors, and refrigeration plants. The division can also be made on different sections or places of the production.
The division of the electricity consumption is done by examining the effect of the devices and the service time. A wattmeter gives the effect, and the staff can usually tell, how many hours a day the device is in service. It is difficult to get precise figures, unless measuring over a period.
The important thing about dividing the energy consumption on use, is to find the large consumers and the potential savings.
Next step is to evaluate how the energy consumption is, compared to other similar companies, or compared to the theoretical optimum. The energy consumption shall be related to the output, e.g. as watt light per mÃ¬, kWh per produced litre of beer, or kg frozen vegetables. The consumption shall be compared to similar key-figures from other companies in the same line. In the literature list there are mentioned some books with key-figures. As an alternative it must be attempted to get an estimation of the energy consumption from other companies.
Furthermore a comparison with the theoretical energy consumption ought to be done. For a drying installation it can for example be calculated, how much energy is needed to evaporate the water from one humidity to another, in case of no loss.
In this way, it can be discovered, if the energy consumption of the company is higher or dower than the average, and if there are some pans of the production that have a high consumption.
During this first evaluation there can be identified fields which have large savings potentials.
The evaluation is supplemented with a more careful examination of the installations, and any measurements:
- Does the installation need cleaning?
- Is the installation running regularly, or must it be adjusted?
- Is the installation optimal controlled, using the most efficient units in preference to less efficient units?
- Is the installation only running, when it is needed?
- Are parts of the installation worn, and need to be replaced?
- Is a part of the installation so old that new and more efficient exist?
- Is the structure optimum?
- Is it possible to change to a more efficient energy source?
The possibilities are described in details under the individual consumption types.
The savings proposals can be here-and-now measures. Or it can be measures which only are economical, if they are done together with other reconstruction or replacement of the installation.
Concerning each proposal the energy adviser estimates the energy saving, other savings for example reduced water consumption, investment, and any change in running costs.
The rentability of the investment is calculated. Preferably both the present worth and the simple pay back period. It is most correct to use the present worth method, where all present and future receipts and expenditures are referred to the present. The method both tells, if the investment is profitable, and which investment gives the highest profit. The advantage by calculating the simple pay back period is that it reflects, when the saving will be. It is also easier to understand.
All calculations on distribution of energy consumption and saving measures are collected in a short report. When the company has studied it, more details can be presented at a meeting. The company ought to be contacted after some time, to hear, if it has carried out the measures.
If the company isn't very interested in the energy consumption beforehand, it should be proposed to start energy control and management, and appoint a staff to be energy manager.
It is important that it is the direction who appoints the energy manager, or at least take the decision to appoint somebody. Else it will be difficult for the energy manager to get proposals through that cost money.
The energy manager shall monitor the development of energy consumption, and come up with proposals that can reduce the consumption. A simple way of monitoring the energy consumption is to make diagrams or curves, where weekly or monthly registrations of energy consumption, and maybe also water consumption, are kept. Computer data sheets can make the registration easier.
The consumption must be compared to an estimated consumption. If an increase in the consumption occurs, due to a fault in the system, then it is possible for the manager to intervene fast, and straighten the fault.
The energy manager calculates the estimated consumption. The first year the estimated figures will not be that precise, but when registration of consumption has taken place for a period, it is much easier to estimate the future consumption. When the company puts a saving measure into work, the calculated saving must be included in the budget. It may be necessary to install more meters, and maybe timers, in order to divide the consumption more.
Type of Consumption and Conservation
Space Heating and Hot Water
Energy consumption related to heating buildings and hot water, can be reduced by the same measures as for dwellings: Afterinsulation, better insulated windows, tightening, lower room temperature, water saving devices, and lower hot water temperature. The possibilities are described more deeply in the previous paragraph on energy conservation in households.
The cheapest advice is, remember to turn off the light when it isn't needed. Especially at work many people forget to turn off the light. It may be in corridors and storerooms, where the staff seldom is, but where the light anyway is on all day. Or in offices, where the light was turned on in cloudy weather, but was not turned off again, when the sun came back.
Even fluorescent tubes must be turned off. Provided one is leaving the room for more than a few minutes, fluorescent tubes must be turned off. The life span is only slightly reduced, and the extra electricity consumption related to keeping the light on, costs far more than changing the tube a little more often.
To be able to turn off, there must be easy access to the switch. And the lighting must be divided, so the light can be off at a window, and on in the middle of the room. If it is not the case, a modification can be proposed, eventually in relation to other alterations of the lighting.
The second cheapest advice is to keep shades clean. It gives no direct energy conservation, but might cause that some of the lamps can be turned off, because the rest provide more light.
Next step is to change the lighting. The easiest way is to substitute incandescent lamps with fluorescent lamps, and old fluorescent tubes with new, thin, and efficient types. There are many types of compact fluorescent lamps, and by trying these out, the best suitable for the lamp is found. Choose electronic lamps, which can stand being switched on and off more often.
Halogenic lamps save a little compared with incandescent lamps, but not as much as fluorescent lamps. One has to realize that halogenic lamps run on low-voltage, and therefore are plugged through a transformer. Even though the lamp is turned off, there is loss from the transformer, which means that it consumes a small amount of electricity all the time. The loss makes the transformer feel warm. Therefore the switch must be turned off, and not only the lamp.
Large fluorescent tubes installations can have electronic precouplings mounted, to substitute the mechanical ones with coils. They have less loss, and because the frequency is higher than the main's frequency, they provide more light. Moreover they last longer. The high frequency technology gives the possibility to subdue the light, either manually, or by a photoelectric cell regulating on solar incidence.
If there are problems with turning off the light, motion detectors, that turn off the light in a room when it is empty, can be installed.
When having a bigger rebuilding the lighting should be evaluated according to the need of light. Danish Standard has recommendations on, how strong the light has to be, related to the task in DS 700, 703, 705 and 707
The distribution between working light and general light in the room must be evaluated. Maybe the general light can be decreased, if there is a good source of light at the working spot.
Holders and lamps with good reflection should be chosen. At last there is the possibility to choose light colours for the walls to reflect light.
By reducing energy consumption for lightening, the heat from light is also reduced. If the offices are ventilated or cooled, the consumption for this also decreases.
A cheap piece of advice like for the light: Turn off, when not in use. In most offices all computers, printers, photocopiers, telefax machines, etc., are turned on, from the time the first person arrives, till the last one goes home. At larger workplaces some of the appliances are not even turned off before the night watcher makes his round.
Telefax machines have to be turned on day and night, if it shall be possible to receive faxes all the time. Else it might be enough, having it turned on during the day.
Photocopiers are usually used through the whole day, and they must be turned on all the time. Some small photocopiers have no warm-up period, and therefore they are ideal for small demands. They are only fumed on, when a copy is being taken.
Whether the printer can be turned off or not, depends on, if it is connected to one or more users. If there is only one user, it is easy to turn on and off, when printing.
Computers are not damaged by being turned on and off several times a day. Many people turn on the computer when they arrive in the morning, and turn it off when they leave, regardless of it not being used the whole day. Some even have the monitor switched on day and night. It wears the monitor and electronics a little to switch on a computer, but it also wears to have the computer on all the time. And most computers are often replaced by new appliances, before the technical life span is reached.
There may be other small devices in an office, which are coupled to a transformer placed in the plug, like halogenic lamps. It can be an electronic letter balance, a modem, or a charger for a labtop. Even when the device is not in use, there is loss in the transformer, which means it consumes electricity all the time. It is not enough to switch off the appliance itself. Also the switch has to be off.
If it is a problem to remember turning off the appliances, timers that turn off the appliances outside office hours can be installed.
When buying new devices the energy consumption ought to be considered.
Ventilators and Blowers
Ventilation is used for providing a satisfactory indoor climate, and remove unpleasant or toxic substances from a production.
The simplest saving is, only to run the installation, when there is a need. If thermostats, or other automatic, are installed, it must be ensured that they work properly. There can be a need for supplementing the control with timers and motion detectors.
Some ventilation plants can run at variable speeds, and it is therefore possible to choose the performance that fits the need. Moreover exist regulators with infinitely variable regulation of the performance.
Filters on the plant must be cleaned frequently.
Ventilation plants that both draw out air and blow in fresh air, have a heating element to heat the incoming air to avoid draught inconveniences. If it is an electrical heating element, and the room in addition is heated by some other source than electricity, it must be ensured that the thermostat is adjusted as low as possible. One has to find a temperature by experiment, where the staff do not feel draught from the inlet.
If there is no heat exchange between in- and outlet air, the heat consumption can be reduced by a heat exchanger.
The efficiency of the plant might be improved by changing motor, belt drive, or ventilator. It depends on how old the plant is. There can also be some achievement by rebuilding the ventiducts, or other ducts with large drop of pressure.
Blowers are used in production, to move air flows, or products with the air flow. Savings can be obtained by optimum management concerning the demand, cleaning, and replacement of parts with low efficiency.
There are pumps in the heating installation, and there might be pumps moving liquids in the production.
At first it must be secured that the pumps are only working, when there is a need.
Second that the efficiency is adjusted to the demand. A valve reduces the volume flux, but does not save electricity. Some pumps have a built-in regulator with variable speeds, where the lowest performance gives lowest electricity consumption. Some pumps have electronic control for infinitely variable regulation. It is possible to mount the control on pumps without a regulator.
If a pump has to work at both low and high performance, it might be an advantage to rebuild, so there are more pumps being coupled in, according to the demand.
Furthermore it must be secured that the size of the pump is adjusted to the plant. By replacing the pump and maybe the engine, if the pump and the engine are not integrated, the efficiency can probably be increased.
If the piping is poorly made, rebuilding might lower the pipe resistance, and thereby the electricity consumption connected to the pump.
There might be large savings to achieve in relation to refrigeration plants. This counts for plants in both shops and industry.
It must be secured that the plant does not work, when there is no need for refrigeration. This especially counts for freezers, which are only in use during production. Cold stores for storing goods must of course run constantly.
Many refrigerating plants have too low evaporation temperatures and too high condensation temperatures. This leads to high electricity consumption. There must be chosen an evaporator temperature, which isn't lower than the demand. Clean evaporators ensure that enough cold is provided. The condensers must be kept clean as well. The thermostatic control of condenser cooling shall be as low as allowed by the data for the plant.
It is possible to reduce the cooling demand. There might be intrusion of warm air from outside, or there might be heat sources in the room. Maybe the cold store can be better insulated, thus reducing the transmission loss.
There exist various methods to regulate the performance of the refrigeration plant. Improved management can lower consumption.
Some refrigeration plants utilize the condenser heat for space heating or-hot water. This is a good solution, but only if the condenser temperature isn't raised to get hot air or water. Instead it is more profitable to install a heating element for the last heating.
Replacement of motor, and perhaps transmission between motor and compressor, might raise the efficiency.
At last the design of the plant might be bad, which results in too high electricity consumption. This is especially seen, if the original plant has been enlarged to meet a higher refrigeration need.
Compressed air is used by industry to run tools and valves, etc., and to blow products clean.
It must be ensured that the plant is running only when compressed air is needed. The plant must be adjusted to the needed pressure, and not higher. Cleaning of filters in the installation can lower the pressure loss.
The air drawn in must be as cold as possible, as the electricity consumption decreases, when the air density increases. Therefore it is preferable to draw in air from the open.
There might be many leakages in the piping. By tightening, the compressor performance is decreased, and with this the electricity consumption.
As regarding refrigerator compressors, there are more ways to control them. Changing the regulation might in some cases lower the consumption.
If the air compressor is only used for pneumatic tools, it might be an advantage to scrap the plant, and use electric tools instead.
If there is a heat demand at the factory, it is possible to regain the heat from the compressors.
Engines are used in industry for running machines, belt conveyers, etc.
It must be ensured that engines are running only when needed. All parts must be regularly cleaned and maintained.
The engine size must fit the demand of the appliance. Often the engine is oversized, causing too high electricity consumption. By alternating need of performance, electronic regulation results in the lowest consumption. It is also possible to have more engines of different size, or one engine which can work at two speeds.
If the engine is low-efficient it might be profitable to change it.
Heat can be used for heating, evaporation, drying, melting, etc.
The energy source is electricity or fuels like natural gas, oil, and solid fuel. Energy economic it is in general advantageous to utilize the fuels, as loss at the power plant is avoided. Though electrical heating might be easier to control than fuels.
The process heating must be controlled, so there only is consumption when there is a need.
The demand must be decreased as much as possible, for example by insulation to less heat loss. As we]l as the temperature must be lowered as much as possible.
Concerning drying processes, the consumption can be decreased by removing as much moist as possible before the drying, for example using a hydro extractor.
It might be possible to regain heat from a heated product, and use the heat to preheat a new product.
If fuels are used for heating, the combustion must be with smallest possible loss. Air inlet must be adjusted to maximum efficiency. A poor insulated boiler can lower consumption if insulated.
Energistyringshandbogen (The Energy Management Handbook). Foreningen for Energistyring.
Handbog i energiradgivning (Handbook in Energy Advisory), eight volumes. Danske Elv'rkers Forening.
Dansk Standard (Danish Standard), DS 700, 703, 705 and 707.
The rays of sun light each year provide the earth 20.000 times the energy we consume. Even the roof of a single-storeyed house in not very sunny Northern Europe receives ten times as much energy, as the house needs for heating.
Gunnar Boye Olesen, Copenhagen Environment and Energy Office
Though human cultures have used solar energy for millenniums, solar heating systems are a new technology, which has been utilized in Europe since the end of the seventies. Today so]ar heating plants are profitable in many situations in Europe. This is primarily true for plants heating domestic hot water and swimming pools, various solar drying plants, and simple passive solar heating design.
Energy from the Sun
To design solar heating systems, a general view of energy content, variation, and characteristic of the solar irradiation is needed. In Northern Europe the energy content is more than 10 times bigger during summer months than during winter months (in Southern Europe 5 times), and it varies appr. 20% between sunny and not very sunny years.
A great deal of the solar energy is In Northern Europe received as diffuse radiation, which means energy irradiation from the sky, and not directly from the sun. The diffuse radiation can be captured by flat plate solar collectors; but it can not be concentrated by mirrors. This is the reason, why concentrating solar collectors have a relative small output here, compared to other parts of the world, where the amount of direct solar irradiation is bigger.
Theoretically the optimum location of a solar collector is a south facing surface, with the same tilt angle as the latitude of the place (Denmark is located at 56› North). In practice there will always be shadows at the horizon, which means that the optimum is a slightly more level location. If the wish is to optimize on respectively summer and winter output, the tilt angle of the solar collector must be more level respectively more sheer.
A small deviation from the optimum orientation and inclination of a solar collector is not of practical importance, cf. the figure above and the following section on efficiency of solar collectors. In Denmark solar collectors are installed up to 60› from south.
A solar collector that traces the sun, will receive about 20% more solar radiation than a south facing optimum placed collector. This additional output does not compensate the costs related to a construction, which has to trace the sun. Usually it will be cheaper to install a 20% larger solar collector.
Active Solar Heating Installations
Domestic Hot Water Systems
The most widely distributed utilization of direct solar heating is for hot water production. An installation consists of one or more collectors in which fluid is heated by the sun, plus a hot-water tank where water is heated by the hot liquid.
In Northern Europe a solar heating plant can provide 50-70% of the hot water demand. It is not possible to obtain more, unless there is a seasonal storage. See the example at the end of this section. In Southern Europe a solar heater is able to cover 70-90% of the hot-water consumption. In Northern Europe a solar heating plant for hot-water has an energy pay back period of 3-4 years (see also chapter 4).
The simplest installations are the thermosyphon systems, with the storage tank placed above the solar collector. The temperature difference between the solar collector and the storage forces the circulation of the collector fluid, when the sun is shining, and heats the solar collector. This type of installation is popular in sub-tropical and tropical areas, especially units with integrated solar collector and storage tank. It is more difficult to utilize the thermosyphon solar collectors in Northern Europe, because of frost problems with the storage tank.
Solar water heaters are very popular in places dike Greece and Israel. They are now gaining a footing in Northern Europe, e.g. in Denmark where both the State and popular energy offices have put a lot of work into solar heating campaigns aimed at single-family houses.
For summer purposes there are many simple systems, that provide hot water when the sun is shining. Both self-builder systems and complete systems, e.g. for camping.
Solar Heating for Combined Space Heating and Hot-water
An active solar heating plant can provide hot water, and additional heating via the central heating system at the same time. To get a reasonable output, the central heating temperature must be as low as possible (preferably below 50›C), and there must be a storage for the space heating. A smart solution is to combine the solar heating installation with under-floor heating, where the floor functions as heat storage.
Solar heating installations for space heating usually give less profit than hot-water installations, both according to economy and energy, as heating is seldom needed in summer. But if heat is needed during summer, then space heating installations is a good idea.
In Northern Europe a solar heating plant can cover up to 30% of standard annual heat demand. In some places like the Alps, the total consumption can nearly be covered, as heat is demanded all year round, and winters are simultaneously sunny.
Solar Heated Swimming Pools
If one wants to heat up a swimming pool a few degrees above the outdoor temperature, a simple solar heating plant can be used, where the pool water is pumped through plastic collectors without cover. Due to low price and high output, this kind of solar collectors have become very popular in several places in Europe, first of all for outdoor swimming pools.
Solar Heating for District Heating Plants
Large solar heating plants for district heating are now in use, e.g. in Denmark and Sweden. Large so]ar modules for this purpose are constructed, which are practical to install directly on the ground in larger fields. Without a storage a solar heating installation can cover appr. 5% of the annual heat demand, as the plant must never produce more than the minimum heat consumption, including the loss in the district heating system (by 20% transmission loss). If there is a day-to-nighf storage, then the solar heating installation can cover 10-12% of the heat demand including transmission loss, and with a seasonal storage up to 100%.
Another possibility is to combine district heating with individual solar water heaters. Then the district heating system can be closed during summer, when the sun provides hot water, and there is no need for space heating.
To cover the total heat consumption by solar energy in a house in Northern Europe, a storage that stores heat from summer and autumn is needed. Since water is a very efficient storage agent, a lot of experiments with large water storages have been carried out. Actually a house can be heated all year round by a solar collector combined with a super-insulated tank with the same volume as the house. But in practice this solution is far too expensive.
The most promising seasonal storages are large storages in connection with district heating, because large water storages are cheaper and with less loss per m than smaller storages. Some pilot and demonstration plants with seasonal storage have been built in Sweden. They have experience on seasonal storages in concrete tanks. in pools with insulated cap, in blasted rock caves, and in bore holes where the heat capacity of the soil contributes to the storage.
Drying of Crops and Houses
A solar collector that heats air, can be used as a cheap heat source for drying corn and other crops. The solar air-collector may consist of a black mat covered by a plastic plate. The air is drawn through the mat, where it is heated, and thereafter blown through the crops.
A damp house or room can also be dried out by blowing hot air from a solar air-collector into it. By using a photovoltaic driven blower, it can be secured that air is blown in only when the sun shines. Such installations are commonly used in summer cottages in Denmark and Sweden, where they keep the houses dry most of the year.
High Temperature Solar Collectors
If temperatures over 100›C are needed, e.g. for industry, or steam to generate electricity, there exist various possibilities with high temperature solar collectors. The most successful type is a concentrating solar collector made by Luz, a parabolic trough reflects the solar radiation to a black tube in the centre of the trough. This type is used at some solar power plants in California, but it would not be very efficient in Northern Europe, while it can not make use of the diffuse solar radiation. In Europe are manufactured flat-plate solar collectors with evacuated tubes, which can produce heat at temperatures from 100 to 200›C. Furthermore flat-plate solar collectors covered by air glass (an efficient, transparent insulation material), for the temperature range 100-200›C are under development.
Finally exist some pilot plants, e.g. in France and USA, consisting of a large number of mirrors that reflect the solar radiation onto a central absorber, where steam is produced and used for power production.
Design of Solar Heating Plants
Most solar heating plants are designed by simple hand rules or the f-chart method. As the exact consumption seldom is known, more exact computer simulations are not used for design, unless the plant is very big or very special.
According to solar water heaters (heating from 8 to 45›C) with south facing, oblique solar collectors, which have selective absorbers, the following hand rules can be used:
* 1-1.5 m: solar collector area is needed per 50 ltr daily consumption of hot water
* the storage tank shall be 40-70 ltr per m: solar collector
* the heat exchanger in the storage tank shall be able to transfer 40-60 W/›C per mÃ¬ solar collector at 50›C.
If these guidelines are followed, a solar water heater installed in Northern Europe will cover 60-70% of the annual hot water consumption, and will be able to produce 350-500 kWh/mÃ¬. With an installation like this, the additional heating can be turned off during 3-5 summer months, and idle loss from a furnace is cut.
A family with 4 persons uses 50 litre of hot water per person every day. It is heated by a furnace with an efficiency of 80%, and an idle loss of 500 kWh/month.
They choose a 5 mÃ¬ solar collector (1.25 mÃ¬ per 50 ltr daily consumption). The storage tank then has to be 200-350 litres.
They save appr.:
65% of energy for hot water
idle loss, 4 month
transformation loss, furnace
(20% loss in furnace)
Total saving per year
= 500 ltr of oil
The family, which is living in Denmark, is going to change hot-water tank, and can choose between a new hot-water tank at 6,000 DKK, or a solar heating plant at 34,000 DKK, both prices include VAT and installation. As the storage tank in the solar heating plant can replace the ordinary hot-water tank, the family saves the money for this.
Net expenditure by choosing solar heating instead of just a new hot-water tank will be:
Solar heating plant
New hot-water tank, saved
+ 6.000 DKK
State subsidy, appr.
- 9.000 DKK
The annual net saving will be:
Saved oil, 500 ltr at 4.20 DKK
Operation and maintenance, appr
+ 300 DKK
Total net saving, annually
For the family in this example, the solar heating plant has paid itself back in ten years (quicker if there is inflation). The expected life span of the plant is 20-30 years.
If solar collectors with non-selective absorbers are used, a 30% larger area is recommended. Low-flow installations and thermosyphon plants can produce up to 20% more than plants with a circulation pump. The guidelines above are though recommended also for these plants.
If a solar heating plant isn't optimum placed, then output and part of supply are reduced as shown in figure 8.9.
The F-chart Method
If a more detailed calculation than the guidelines above is wanted, the f-chart method can be used. With a small computer program based on this method, a solar heating plant can be designed quickly. In Denmark the most popular computer soft-ware of this type is the solar package from Energy and Environment Data. By using the f-chart method, it can be estimated how much a solar heating plant will produce month by month. For the calculations data are needed on monthly solar irradiation, outdoor temperature, the efficiency equation for the solar collector, heat loss from the storage tank, transmittance of heat exchanger, and consumption. The method is based on empirical figures for, how much a solar heating plant produces. Thus it can only be used for systems, where sufficient experience exists.
Construction of Active Solar Heating Systems
In the following the construction of a solar water heater is described. Solar heating plants for some other purposes are built up in a similar way.
The description gives some idea of the richness in details, one has to consider according to solar heating constructions. One should not be led to believe that it is possible to build a solar water heater just based on this description. One should only tackle this when experienced in plumbing, and in touch with people experienced in solar heating.
The Solar Collector
The main part of the installation is the solar collectors. They consist of a glass or a plastic cover, an absorber where the solar radiation is transferred to heat in the solar collector fluid, insulation along the edge and under the absorber, and a case that holds everything together, and allows the necessary ventilation.
When glass is used as cover, it is important that the iron content is low or zero, so at least 95% of the solar radiation passes through the glass. There are several disadvantages of using two layers of glass, so in practice always a single layer is used. If a plastic cover is used, it is important that the plastic can stand up to the UV-rays from the sun. It has been found that polycarbonate plates are very satisfactory. Often two layers of plast are used, e.g. channel plates can be used.
The absorber can be made of a plate with tubes where the collector fluid flows, of finned tubes (named sun-strips after the manufacturer), or simply tubes. The absorber is often covered with a selective black coating, which absorbs the sun rays, but holds back the heat radiation. Usually the absorber is made of copper, stainless steel, or plastic; sun-strips are copper tubes with aluminium fins. A lot of experience has shown, that absorber tubes made of ordinary steel or aluminium cause big problems with corrosion. It is essential that the absorber can stand up to the UV-light from the sun and the stagnation temperature (dry-boiling temperature), which is 100-140›C for solar collectors without selective coating, and 150-200›C with selective coating.
Usually solar collectors are mounted directly on top of the roof, or at a frame placed on a flat roof or the ground. Solar collectors can also be integrated in the roofing; but because of troubles with sealing between the solar collector and the rest of the roof, this is only recommendable, when a huge part of the roof is covered with solar collectors.
The Storage Tank
The storage tank shall store the solar heat. This is done by storing hot water until it is needed. The most efficient is a vertical tank with good temperature stratification, so the cold inlet water isn't mixed with the warmer water at the top of the tank. A horizontal tank reduces the output by 1020%.
The insulation of the tank must be so good, that hot water from a sunny day is still hot two days later. Especially the top must be well insulated, and without thermal bridges. It must be ensured that piping from the storage tank does not lead to self-circulation, which can drain the tank for hot water during periods without hot water consumption. If there is a flow tube pipe for the hot water, this must not be connected to the cold water, but has to enter at the upper part of the tank.
Usually the outlet of the storage tank is equipped with a scalding protection, so the water delivered for use never gets warmer than e.g. 60›C, regardless of the temperature in the tank.
The heat from the solar collectors is delivered to the water in a heat exchanger. As heat exchanger is mostly used a coil in the bottom of the tank, or a cap around the tank with collector fluid. In low-flow and self-circulating systems always a cap is used. In low-flow systems the solar collector fluid flows slowly down through the cap of the storage tank, which gives a stratification of collector fluid in the cap corresponding to the stratification in the tank. This gives more ideal heat transfer, and thereby a higher efficiency than. in traditional systems.
Solar Collector Circuit
The solar collector circuit connects the solar collector to the storage tank. The components of the circuit are:
* a pump that ensures circulation (not needed in self-circulating systems). The pump is usually controlled by a difference thermostat, so if starts running, when the solar collector is a bit warmer than the storage tank. If the storage tank has a heat exchanger coil at the bottom, a more simple control system can be used; e.g. a light censor, or a timer that starts the pump during day time.
* a one-way valve which prevents the solar collector fluid from running backwards at night, and emptying the storage tank for heat (not necessary in all kinds of installations).
* an expansion tank; either an open container at the top of the installation, or a pressurized expansion tank that contains minimum 5% of the solar collector fluid.
* overpressure protection (only in connection with pressurized expansion tank); must be a type that manages to let out the solar collector fluid, if the system is boiling. There must always be an accumulation tank for the fluid in case of boiling.
* air outlets, automatic or simply screws; must be used at ALL height points in the system, as air pockets will always appear.
* filling valve
* dirt filter for the pump, to remove dirt, e.g. from the installation (can be spared in some installations)
* manometers and thermometers according to the need
The solar collector piping must be of a non-corroding material. Systems with open expansion are most risky to get corrosion problems.
The solar collector fluid must be able to stand frost, and must not be toxic. Usually an approved liquid is used, consisting of water with 40% propylene glycol (can stand "20›C), and a substance that can be seen and tasted, if solar collector fluid leaks to the tap water. Also oil can be used as collector fluid, but it is very difficult to make a collector circuit with oil tight.
Operation and Maintenance
When the solar heating system is in use, there is not much to take care of. Once or twice a year it must be controlled that there is enough fluid and pressure on the system. Once a year it should be checked that the solar collector fluid hasn't become acid. Use indicator paper. Acid fluid should be changed.
In case the system is boiling, it is simply needed to fill new fluid on the system; as the old fluid may be damaged by boiling.
Some storage tanks must be decalcified? and the anti-corrosion zinc block shall be changed in appr. 10 years. it prolongs the life span significantly
Building Design with Passive Solar Heating The most simple form of passive solar heating is orientation of the windows, so all larger windows face south (+45›). A house with south facing windows needs 15-25% less heat supply than a similar house with east and west facing windows.
Saving is the largest, if the inner part of the house is built of heavy materials that absorb heat, and if the house has low energy windows.
Large south facing windows ought to be combined with shadowing overhangs that prevent overheating during summer. Passive solar heating design is popular in some places in the USA, e.g. in New Mexico, where there is barely built a house without passive solar heating considerations. More and more European architects use passive solar heating design for new buildings as well as renovation.
An unheated glass annex at a south front (south +45›); e.g. a greenhouse, a glazed-in balcony or patio, contributes to the heating. The heat saving is due to three conditions:
* the extra layer at the front insulates
* the sun heats up the glass annex, which further ;educe the heat loss from the facade behind the glass
* the air in the glass annex can be used as heated ventilation air in the house.
Roughly estimated, the glass annex can save half of the heat loss from the facade behind it. The saving totally depends on, how the house and the glass annex are used. If the doors and windows between the house and glass annex are not closed, or the glass house is heated, it may result in a higher heat consumption than without the glass annex.
The heat conservation due to a glass annex does not justify its construction, neither economic nor energy-economic (the energy pay back period is 10-14 years). The reason why glass annexes are still popular in Northern Europe, are the possibilities they provide, such as extra living space when the sun is shining, or a greenhouse; and they reduce the need for maintenance of the facade.
A solar wall is a glass plate or transparent insulation on the outside of a wall. If the space between glass and wall is ventilated then the construction is called a ventilated solar wall. If the wall is heat conductive and a poor insulator, e.g. a solid brick or concrete wall, it will be heated during the day, and give off some of the heat to the rooms behind it in the evening and at night. A ventilated solar wall can contribute to the heating of ventilation air.
Solar walls have some distribution in the USA, e.g. in New Mexico. A number of demonstration installations with solar walls exist in Denmark and Sweden; but they are not very common in Northern Europe yet. The energy output from solar walls made of ordinary materials is 50-200 kWh/mÃ¬ in Denmark, and a little higher when if of high-efficient insulation materials, e.g. air glass.
Solar walls are also known as trombe walls. named after the French Mr. Trombe who was one of the first to describe it.
Passive solar house with seasonal storage
If a house is built into the soil without insulation against it, the soil can be used as a seasonal storage. The ground must be insulated up to 6m from the house, and rain and ground water must be kept away. The temperature fluctuation in the house will not exceed 4-5›C between summer and winter, even with sun as the only heat source.
The system is developed in the USA, where it has been in use since the beginning of the eighties. The first house of this type in Denmark is built in 1991, and there is not much experience on, how this house type fits in North European climate.
1. Energihandbogen (The Energy Handbook), Judith Winther et.al. OVE's forlag, Copenhagen 1981.
2. European Solar Radiation Atlas vol 1. Commission of the European Communities 1984, EUR 9344, ISBN 3-88585-194-6.
3. Solar leafing i, Denmark small plants. The Danish Information Secretariat on Renewable Energy, 1991.
4. Byggehandbog for solvarme (Building Handbook on Solar Heating). Palle Ladekarl, Torben Skott. Aage Johnsen Nielsen. OVE's forlag, Copenhagen 1985.
5. Solar Heating in Denmark large plants. The Danish Information Secretariat on Renewable Energy, 1991.
6. Passiv solvarme projokteringsvejledning (Passive Solar Heating, design guidelines) Ministry of Energy, Solar Heating Program Report no. 30. Danish Technological Institute, Heating Technology and Institute of Thermal Insulation. Technical University of Denmark, 1985.
7. Passive Annual Heat Storage' Improving the design of Earth Shelters. John Hait. Rocky Mountain Research Centre, Missoula in Montana USA, 1983.
8. Solar Engineering of Thermal Processes. John A. Duffie, William A. Beckman. Wiley-Interscience publication, New York 19X0
9. Vedvarende Energy i Danmark (Renewable Energy in Denmark). Preben Buhl Pedersen, Jan Viegand and Niels 1. Meyer. Physical Laboratory Technical 111, University of Denmark, Lyngby 1990.
Hans Jakob Jakobsen, Architect, The Energy and Environment Office in Aarhus.
Within the last 15 years use of glass in the south facade has been increased, to make optimum use of solar energy for heating - also called passive solar heating. In this category we find glass annexes. People's demand for comfort, and desire of bringing the green spaces indoors, linked with energy savings, often leads to the needed enlargement of the house. The glass annexes are very different in construction types, appearance, and functions. Many property development companies have for example offered houseowners glass houses with double glazing and additional heating. The energy offices find this kind of glass annexes both unecological and expensive, as the saved energy does not compare with the fossil fuel used for heating in periods without sun.
Construction principles for "proper" glass annexes
Some energy offices have been responsible for construction of glass annexes during the last years. The construction principle is the same, whether it is an extension of an old house or a part of a new building.
The glass annex is built at the outside of the house. The facade it leans onto, is viewed as a "closed" facade with ordinary windows and doors. The glass annex itself is single-glazed. A further function of the glass annex is protection of the house against wind, rain, and frost. The bar types vary. Usually either wood or aluminium constructions are used. Aluminium needs less maintenance than wood, but on the other hand more energy is used for processing aluminium than for wood. Glass annexes made of wood have thicker bars than aluminium types, resulting in less solar incidence for wooden constructions.
The glass annex must be seen as an unheated outdoor room, where it is possible to stay most of the year. Every time the sun is shining, even if it is freezing 10-15›C, the glass annex can be used. Temperatures up to 25›C have been measured on December 21st, the shortest day of the year, in one of the glass annexes Vestergade 75 in Aarhus, which is described later in this paragraph.
One layer of glass is sufficient for a glass annex. Measurements have shown that the house is not supplied with more heat, when two layers of glass are used, then the glass annex needs more ventilation. Furthermore it is secured that nobody is tempted to heat it during cold periods, e.g. with electric heating, in order to extend the use of the glass annex. In other words, as long as the glass annex is warmer than the house, the door between can be left open, to heat the house by the sun.
It is furthermore important, that the glass annex is sufficiently ventilated. The best will be, if appr. 25% of the glass building's roof area can be opened. This provides against overheating, that for example would burn green plants quickly. The ventilation funkier provides against mist formation on the windows.
The Energy and Environment Office in Aarhus has been involved in several projects with glass annexes. I have described some of these in this text.
Green City Projects
The first example is two glass towers, that are built on a south facing facade. The house has had balconies earlier, but these were knocked down 5 years ago.
In spring 1990 the Danish Energy Agency stood with a money bag ear-marked for green demonstration projects in the city.
In the light of this, a co-operative housing society in Aarhus addressed the Energy and Environment Office in Aarhus and asked us to help them with good ideas for improving the energy system of the house. As part of our house visit service we took a look at the building. The building orientation, with a south facing facade. was evident for placing two glass towers.
The dead-line for applying was short, appr. 14 days. Within these two weeks the project should be formed, approved by the occupiers of the house, and an application had to be written. The project involved two glass towers, 5 storeys each. Each of the ten flats has got an 8 m glazed-in balcony. The project group, which consisted of The Cooperative Building Society Vestergade 75, The Engineer Croup Aarhus, and Aarhus Energy and Environment Office, got a positive answer to their request in November 1990. 329,-00 DKK was allocated to the project.
The Project Phase
After the grant from the Danish Energy Agency was gathered in; authority phase, apply for building licence, definitive building licence, project phase, construction, and opening followed in rapid succession.
In addition to providing its occupiers a nice unheated glazed-in living room, the project is a demonstration project. A new measuring method, a so called photogrammetric measuring of the house facade, carried out by the Architecture School in Aarhus, has made a quick and precise measurement possible. This makes the construction easier, as the aluminium front elements can be produced at a factory, and built up directly at the place without further cutting out. The bearing construction of the glass tower is also a new system, with the slight, fireproof steel uprights built into the facade. This system gives the house a light character, and larger solar incidence. The balcony floors are made of prefabricated concrete elements.
Green Room with Energy Savings
In addition to savings on the heat bill, the green room added to the city flats is important. A room that quickly becomes the centre of the house. The glass towers made in aluminium are nearly free of maintenance, and easy to clean. Aluminium has very long durability, so even though the towers have cost 700,000 DKK, they will pay themselves some day.
The energy saving, which is 10-15%, has cost each flat appr. 45.000 DKK in building expenses, after deduction of state support.
Renovation of Old Balconies
The second example shows, how old balconies can be renovated, instead of knocked down and rebuilt. This saves resources and money.
At Tvedvej in Kolding, Kolding Cooperative Housing Society of Public Utility has finished a project, where old balconies have been renovated, partly by building a glass "coat" around the old balconies, /1/.
The 48 flats were constructed in the middle of the 50'es. Instead of bringing the standard and quality back to the original level, the cooperative housing society decided to add new elements to the balconies.
The 48 flats have become a demonstration project, selected and supported by the Danish Ministry of Energy, because the balconies have been covered by glass, thus getting the character of a glazed-in patio.
Utilization of Passive Solar Heating
The cooperative housing society sought cooperation with the firm Jens (filling A/S as well as engineers and architects. From this advisory group came a proposal, which included the Gilling firms balcony closure unit called Altermo - a glass unit made of single layer glass. The central part of the glass unit is a sliding door, which ensures good ventilation in the glazed-in livingroom. The glazing covers the building from ground to attic. forming a glass tube in all. The outdoor glazed-in livingrooms insulate, and at the same time protect the concrete against rain and frost.
The glass annexes have, in addition to providing heat for the flats, contributed with a new utility value for the occupiers of the house. The balconies, which earlier were windy places to stay, have nearly rendered the living rooms superfluous.
Low Construction Price
The renovation of the building's balconies with glass units have cost the cooperative housing society 1.43 million 1)KK. The total renovation of the houses, which among other things included also insulation of the facades, cost in total 5.7 million DKK. The house rent has raised after the renovation, but the housing company and the tenants expect to cover part of these expenses through heat savings. The housing company in Kolding conservatively estimates a total heat saving of 16%, while Aase Gilling from Jens Gilling A/S estimates the theoretical saving to be about 50% for the total project.
The House from the 60'es Got a Long Needed Architectonic Lift
The main purpose of the windows in a house is to ensure sufficient daylight in the rooms. But together with the daylight, lots of solar heat also flows into the house. Sun captured through the windows covers appr. 10% of the heat demand in the house.
Nature into the House
This was what the Kock family did in fall 1989, when they saw a reference to the new subsidy scheme for glass annexes, /2/. This scheme for state subsidy to passive solar heating, which provided up to 30% subsidy, has unfortunately been dropped.
The family, who lives in Harlev north of Aarhus, for many years had a glazed-in patio on top of their list. But the many prefabricated glass houses from the timber market never appealed to them. If they should have a glazed-in patio, it should be taylormade for their L-shaped ` house from the 60'es.
After their first contact to the Energy and Environment Office in Aurhus the two architects at the office, Erling Nielsen and Hans Jakob Jakobsen, made a few suggestions for a 12mÃ¬ glass annex. When the sketches were ready, drawings were made for the authorities, and state subsidy was applied for. To get the subsidy, it was necessary to have a sanction from the Test Station for Solar Heating! Danish Technological Institute.
The glass annex, which is made in white-painted wood, was ready for use in April 1990. After a few years use the family members agree on, that the annex has meant a lot for comfort and living in the house. Often the Kock family sits in the glass annex until late in the evening.
Taylormade Costs a Little Extra
The glass annex has been slightly more expensive than usual, because of the adjustment to the existing house. The glass annex has cost appr. 95,000 DKK, from this shall be subtracted a state subsidy of 10,000 DKK, so the real cost has been 85,000 DKK. The glass annex lasts for 50 years, when normally maintained. In 50 years the total energy saving will be 75,000 kWh or 7,500 litre of oil.
Energy Gaining from Unheated Glass Annexes
In the following is gone through an example of calculations on a glass house made in light aluminium construction, /3/. The glass annex is built at a new house with windows with 2 layers of glass. The glass annex covers an area of 250 x 800 cmÃ¬ at the south facade of the house. 6 mÃ¬ of the covered area is window area, and the rest is 14mÃ¬ wall area.
U-values for windows:
Recommended U-values for walls:
uninsulated one-brick wall
uninsulated cavity wall
wall built after
1979 0.4 W/mÃ¬›C
If the built-up roof is leaky, and the roof construction is strong enough, then a glass house on the roof is a good solution regarding aesthetic, energy, comfort, and durability. This glass annex is built in Elsted outside Aarhus.
The Madsen family in Nyborg at Fyn, has chosen to cover their west facing house end with a glass annex. The 30mÃ¬ glass annex is made of painted wood and one layer of glass.
Glass houses are of course also part of new constructions. These terraced houses are built near Copenhagen, and glass annexes cover all the south facade.
1. Carsten Dall, Boligen IO (The Home no. 10), Nov. 1991.
2. Alle taler om miljoet, du kan gore noget ved det (everybody speak about the environment, you can do something about it), Torben skott. Leaflet from the Environment and Energy Office in Arhus.
3. The Test Station for Solar Energy, Danish Institute of Technology, Hoje Tastrup (near Copenhagen).
Ole Rahn, Viborgegnens Energy and Environment Office
Photovoltaic cells are used for producing electricity, where the previous mentioned solar technologies produce heat. Photovoltaics can be used for many purposes. But in grid-connected areas they are still not economically competitive.
Houses in remote areas can profitably use photovoltaics for lighting, cooling, communication, and TV. For pleasure boats (sailing boats) it is a big advantage to use photovoltaics for recharging batteries, and supply for instruments, navigation light, radio, light, and maybe refrigerator.
Photovoltaic cells are also used for operation of signalling lights for navigation and aviation. E.g. the light buoys that mark the submerged rocks, when entering through the Swedish skerries to Gothenburg, are equipped with reliable photovoltaic cells.
In the developing countries there are other purposes. The photovoltaics are used for operation of refrigerators for vaccine and medicine. Photovoltaic installations are often utilized for pumping drinking water and irrigation. The Photovoltaic cells are also used for operation of transportable dental clinics, smaller machines, plus for light, radio, and TV.
Many signal and communication installations are equipped with photovoltaic cells. At the South Indian railway from Madras to Cap Comorin many signal devices are driven by photovoltaic cells nowadays. In China, amplification stations for telephone connections in desert regions are equipped with photovoltaics.
The French physicist Alexandre Edmond Becquerel discovered in 1839 that some copper oxide electrons could produce electrical power, when they were lighted.
Charles Fritts, who produced the first photovoltaic cells from selenium in the 1988'es, predicted already then, that future buildings would be covered by photovoltaics for electricity production.
The first photovoltaic cell of silicon, which had an efficiency of appr. 6%, was produced by Fuller, Pearson and Chapin in 1954 at the Bell Laboratories in the USA.
In 1958 the first photovoltaics were sent out in space by the satellite Vanguard 1.
The development in space travel and research was the force behind the development that took place with photovoltaic technology in the 60'es and the 70'es. One of the most well-known installations from that time is the American Skylab, that was equipped with a photovoltaic plant with a nominal effect of appr. 20 kW.
The tremendous increase of energy price in the beginning of the 1970'es led to, that big amounts were invested in improving the photovoltaic technology. The development has gone through several generations, each with improved efficiency, increased life span, and lower production price. One of the significant conquests is the mass production of cheap amorphous (poly crystalline) silicon cells.
Today a large choice of products exists, that utilize photovoltaic processes for energy supply Pocket calculators, wrist watches, and signal devices for navigation and aviation, are just a few examples from our daily life.
A photovoltaic cell is a component that is able to convert radiation of light into electricity.
Photovoltaic cells arc made of a semiconductive material like selenium (Se), amorphous silicon (a-SiGe), crystalline silicon (Si), gallium arsenide (GaAs), copper/indium diselenide (CulnSe2) or cadmium telluride (CdTe). In bright weather the silicon cell produces appr. 0.5 Volt and appr. 25 mA per square centimetre surface, or in other words 17-13 mW/cmÃ¬.
Photovoltaic cells arc produced of semiconductors, in which a light sensitive area, a PN-junction is made near to the surface, where entering light is able to form positive areas. The charge of the PN-junction, which partly origins from grafted impurities, creates an electric potential. As there is a potential, and the entering light transfers energy to free electrons, then the photovoltaic cell can work as an electromotoric energy source - a generator.
The photovoltaic cell's sensitivity regarding specific wavelength's of light depends on, if the light is able to pass the surface of the cell, pass through the upper layer of the cell, and still have enough energy left to form a positive area in the PN-junction.
Today various usable types of photovoltaic cells exist. Mono crystalline cells, poly crystalline, and amorphous cells.
Silicon is made from quarts (SiO2), which exists in large quantities in nature. The used silicon must be very pure, and for the production a lot of energy for heating is used. Also strong chlorine-containing compounds and bichloride are used. The pure silicon is doped (polluted), e.g. by boron, and thereafter various substances are steamed on.
1. Bus bar, 2. Metal grid, 3. Diffuse N-type layer, 4. NIP layer, 5. P-type doped base material, 6. P-type contact material.
Parts of the production processes are secret, as a costly development is taking place. The development is heading toward still thinner substrate cells, double function cells, and tandem cells. In the future we will also see granular photovoltaic cells with lower efficiency, but at a considerably lower price than todays photovoltaic cells.
Solar Radiation and Efficiency
The solar irradiation outside the Earth's atmosphere' the solar constant, is appr. 1350 W/mÃ¬. At the ground the solar intensity is about 1000 W/mÃ¬ on a clear summer day in Denmark.
The efficiency is calculated as the percentage difference between the irradiated effect (Watt) per area unit, and the effect supplied from the photovoltaic cell.
There is a distinction between theoretical efficiency, laboratory efficiency, and practical efficiency. It is important to know the difference between these terms, and it is of course only the practical efficiency which is of interest to users of photovoltaics.
Silicon cells have a theoretical efficiency of appr. 28% and a practical efficiency of 14 to 16% (1992) By using other semi-conductive materials and other production methods, the efficiency can be increased.
The sunlight has its maximum relative intensity from 450 to 500 nanometre - in the blue light area. Therefore it is important to make the photovoltaic cell with maximum sensitivity close to that area. A photovoltaic cell looks bluish. It is because the blue light, that is containing most energy, is partly reflected from the cell. A typical silicon cell has its largest relative sensitivity in the area 700 to 900 nanometre - that is the infrared area. This missing coincidence is one of the reasons that photovoltaic cells do not have a specially high efficiency, and it is one of the areas being developed.
Another reason for the low efficiency is reflections from the cell surface. This can he met by anti reflective coatings, or by working out the cell surface as many small pyramidal structures.
The photovoltaic cell's efficiency decreases also with increasing temperatures, and they are damaged if the temperature exceeds 60 to 65 degrees.
The metal grid (bus bar and metal fingers) at the surface of the cell, which is used for collecting electrons' reduces the light sensitive area, and decreases thereby the efficiency of the cell.
The main part of the development of photovoltaic technology takes place in the USA, Japan, and Germany. Especially in Japan enormous sums are invested in developing photovoltaic cells, and Japan has gained a great share of the market from USA during the latest years. In Germany remarkable results and high efficiency have been achieved by experiments in laboratories. In Denmark there is also one company working with development of photovoltaic cells.
One of the problems with the in general environmentally compatible photovoltaic cells is, that the consumption of strong chemicals connected to the production is high. They. believe they have solved this problem at the Danish photovoltaic cell factory Solel Energy now. The company has developed a strongly simplified and considerably more environmentally compatible production process, than the others known.
When designing a photovoltaic installation a lot of things must be taken into consideration, if an optimum solution is wanted.
At first it must be clarified, how much energy is demanded from the photovoltaic installation. After that the total daily consumption in Ampere hours (Ah) must be estimated. From the total daily and weekly consumption the total energy storage capacity can be calculated. It must be considered how many days the installation shall be capable of functioning without sun. At the end it can be calculated, how many photovoltaic modules are required to produce sufficient energy.
The tilt angle and orientation of the photovoltaic modules have big influence on the irradiated effect. In Northern Europe the optimum tilt angle is between 35 and 40 degrees, and the modules shall preferably be oriented towards south. A standard photovoltaic module like Siemens M 55 S has a maximum effect of 53 W by a voltage of appr. 13.8 V, and measures 1.3 m 0.32 m.
An installation for a summer cottage can for example be built of two 55 W photovoltaic modules, a regulator box, and a 100 Ah battery.
Such an installation can supply energy enough for lighting, TV, and a small refrigerator, during the summer months.
When more photovoltaic modules are combined in electrical series connection and parallel arrangements, it is important to mount by-pass diodes and string diodes. The diodes have to protect the photovoltaic cells against damaging fault currents, which can appear, when the modules are partly shadowed, or some modules are defect. The photovoltaic cells can not stand up to, that the current runs backwards under any operational condition, normal or not. Many photovoltaic modules are by the way mounted with by-pass diodes from the factory. String diodes must be mounted by one-self.
1. Photovoltaic modules, 2. By-pass diodes, 3. String diodes, 4. Consumer.
The photovoltaic application can be combined with other energy sources. A combination of small wind generators and photovoltaics is an obvious possibility. The energy can be stored in ordinary lead batteries, in nickel/cadmium batteries, in sodium/sulphur batteries, or by cracking water to hydrogen.
The author is developing computer software for calculation of photovoltaic installations. The software includes all variables that are important for the design of photovoltaic installations. The software can also calculate the average annual energy production from a certain installation.
1. Photovoltaic modules, 2. Wind generator, 3. Charging regulator, 4. Battery, 5. Inverter, 6. Consumers
Abroad several large grid-connected photovoltaic power plants are erected. The technology is expensive. The photovoltaic cells produce direct current, which is stored in batteries. An electronic unit, an inverter, converts the direct current to three-phased alternating current by appr. 50 Hz. The inverter is regulated by the grid frequency, and it can be automatically synchronized, and connected to the grid. A Danish company, Sunelec, is developing a somewhat cheaper inverter for one-phased alternating current.
Life Span, Pollution
Photovoltaic cells produced today have a durability of at least 30 years. Photovoltaic cells can not be produced or scrapped without pollution, the used batteries can neither. These circumstances must be taken into consideration, when calling photovoltaic cells a supplier of non-polluting energy. Production processes, which harm the environment as little as possible, must be invented.
Future and Perspectives
The mono crystalline silicon cells are today the backbone of professional applications like communication and energy-supply in remote areas. The advantages are high efficiency (relative) and stable operation for many years. The disadvantage is a high price, as this type isn't suitable for mass production.
Thin-film cells and granular cells are the future. The advantage is lower price due to a continuous production. The disadvantages are, that these types are not ready yet, they are not stable yet, and their life span are still short.
The author thinks that within the next 20 years, we will see a large increase in the number of installed photovoltaic plants. Many grid-connected plants will be installed. In future installations the photovoltaics will be integrated in roof surfaces and outer walls.
1. Energi Nyt (Energy News), The Danish Energy Agency. 1992.
2. Forsog med solceller (Experiments with photovoltaics), Silkeborg SolData. 1991.
3. Electronic Design. May 1992.
4. Siemens Solar GmbH, Solarenergie. 1992.
5. Das Solarenergie Buch (The Solar Energy Book). 1992.
Jens H. Larsen, M.Eng, Copenhagen Environment and Energy Office
Wind power is the renewable energy source which has gained the largest commercial utilization in Denmark. At the beginning of 1992 there are thus erected appr. 3230 wind turbines in Denmark, and these turbines generate appr. 2.5% of our tote] electricity consumption.
This chapter aims at, giving an idea of the development of grid-connected wind turbines in Denmark, and some facts about this development. Finally the author gives his view on the current situation according wind power.
At the beginning of this century windmills were commonly used in Denmark. In 1920 appr. 30,000 windmills were in operation at Danish farms. It were the so called canvas flaps windmills and wind wheels, which mainly supplied tractive power directly to the agricultural machines /1/.
Along with the energy shortage during and after World War II, interest in utilizing wind power appeared again. This development reached its peak, when the power utilities erected the 200 kW Gedser Turbine in 1957. The Gedser Turbine was in operation for 10 years without serious technical problems, and was stopped, because it was uneconomic to operate. During our generation's energy crisis in 1972-74, exactly the Gedser
Turbine became the model for design of the Danish wind turbine concept. See further the section Facts on Wind Turbines.
The energy crisis in 1974 initiated design of smaller household wind turbines. The development began at grassroots level, and with many inventors and pioneers involved. The motives were many, and to great extend characterized by idealism and the debate on introducing nuclear power in Denmark. The first commercial wind turbine was sold in 1976. The motive power was from the beginning, and many years in the future, the private sector, with strong roots in the popular energy movement, folk high schools, etc. In figure 9.1 some of the highlights from this development are collected, which are briefly commented in the following.
From 1976 to 1985 it was mainly the private sector that established wind turbines in Denmark. The turbines were either single ownership or joint ownership installations. Joint ownership wind turbines were established by wind turbine cooperatives.
Some turbines were not connected to the grid at the beginning, but today all commercial wind turbines are grid-connected.
From the early 80es the size of the turbines grew from 55 kW, until today (1992) where the mean size of established wind turbines is 200 kW. Today Danish wind turbine manufacturers produce commercial turbines up to 500 kW. See the survey of Danish turbines in appendix 3.
From 1985-92 both private persons and the power utilities established wind turbines. Against a background of a political deal between the government and the social democrats in 1985, the power utilities were enjoined to establish wind turbines. In 1991 the power utilities were asked to establish another 100 MW wind power. Today appr. 75% of all Danish wind turbines are privately owned, and only 25% are owned by the power utilities.
A fundamental feature of the Danish development has thus been the involvement of the private sector. An essential factor in the first stage was 30% state subsidy for establishment of private owned wind turbines. This support was given to the buyer of the wind turbine, thus supporting a private market for wind turbines. Compared to other countries this kind of subsidy has shown to be more efficient in initiating a technological and mercantile development of wind power. The wind turbine manufacturers thus have been able to develop bigger and more efficient machines all the time, while sale to a quite stable home-market has been secured.
An important basis for the establishment of private wind turbines has been agreements on payment rates for electricity produced by grid-connected wind turbines. A 10 years agreement was contracted by private turbine owners and the power utilities. But this agreement was dropped by the power utilities in 1992, and has subsequently been replaced by legislation in the field.
Together with the state subsidy for establishment of wind turbines, private turbine owners got the electricity tax repaid. Fixed payment rates and tax repayment have been the financial basis, and secured reasonable private economy when establishing wind turbines.
Facts on Wind Turbines
The main parts of a typical Danish wind turbine are shown i figure 9.2. This type is called a three-bladed swift runner. If the blades are fixed, the wind turbine is stall regulated. It means that the wind turbine limits its own maximum performance by a fixed number of revolutions. Some turbines, e.g. Vestas, have revolving blades. This gives a slightly better utilization of the wind, up to 8 %. The rotation of the blades is multiplied through a gearbox to an asynchronous motor. Some wind turbines can be coupled to two different generators (for the better utilization of wind). The size of the generator is often used to name the size of the wind turbine. A better name is in fact the rotor swept area, as the production of the wind turbine mainly depends on the swept area. The turbine is regulated by a fully automatic control. Often the turbine is remote-controlled, and operational data are collected through the telephone network.
Figure 9.3 shows the increase in wind turbine size and production, 1980-89. In 1992 450 kW turbines were erected, with a rotor diameter of 35 m, a height of 35 m, and an annual production of 900,000 kWh, which equals the consumption of 250 households in Denmark.
Development in Rotor Swept Area Efficiency
In 1991 the total power production from 3230 wind turbines was appr. 800,000,000 kWh, equal to 2.5% of the total power production in Denmark. ID 1991 the total installed wind power capacity was 410 MW. In the list of established wind turbines 198991 (figure 9.4) appears the distribution on ownership. It shows that single ownership and joint ownership wind turbines are the majority. On figure 9.5 is shown, how the single and joint ownership installations are connected to the grid.
A large number of Danish wind turbines are erected as single standing turbines. Gradually many wind turbine clusters and windfarms have been established. In Denmark a windfarm is defined as a group of more than 5 wind turbines.
Figure 9.6 shows the mean wind speeds in Europe. Obviously Denmark has good wind conditions, especially in the western part of the country.
In order to calculate the production from a wind turbine on a certain location, it is necessary to know the landscape around it. The landscape can be divided into roughness classes. The less obstacles the more windy the landscape is. Trees, farms, forests, and cities slow the wind down. The relative energy content for different topographic conditions is shown in figure 9.7. It shows that wind energy has its maximum at sea, where no obstacles decelerate the wind. In Denmark the main wind directions are west, southwest, and south. More than 50% of the wind energy comes from these directions. A good wind turbine site in Denmark is thus a south or a west coast. Wind comes with strong power from the sea, and reaches the wind turbine without being hindered by topographic roughnesses.
A good wind turbine site in Denmark is in roughness class 1. At such a site a 250 kW wind turbine is able to produce 630,000 kWh/year. An inland site in Denmark will often be of roughness class 2. Here a 250 kW wind turbine can produce 500,000 kWh/year, which is 20% less than in roughness class 1. The experiences from Danish wind turbine projects show, that under existing economical circumstances it is profitable for private persons to erect wind turbines in a roughness class 2. If the construction conditions are favourable, slightly worse wind conditions - roughness class 2.2 - are acceptable. If the wind conditions are
The wind conditions in Denmark are carefully mapped nowadays. there are maps for each region showing where, and how windy the individual sites are /6/.
Wind Turbine Cooperatives
The main force behind the wind turbine development in Denmark has been the initiative and involvement from the private sector. Without this popular involvement, wind power would never have developed to the stage of today. Denmark would probably have been at the same level as other European countries, which are only to establish wind turbines now. To understand this, it is necessary to know some of the background, and the conditions under which the wind turbine cooperatives have emerged.
As mentioned 75% of the Danish wind turbines are privately owned. The private wind turbines are either under single ownership or joint owned by a wind turbine cooperative. The main part, which means 60-75% of the private turbines, are joint ownerships.
The concept of the wind turbine cooperatives historically originates from the Danish cooperative movement. It was, and is, natural to join together in a local area, to solve a joint task. At the same time installation of wind turbines was encouraged by political initiatives and regulations in the wind turbine field. In the beginning a typical wind turbine involved 5-50 families, who joined together to establish a local wind turbine. Gradually, as the turbine size increased, the wind turbine cooperatives grew as well, and have established wind farms with 10-30 wind turbines.
Two main regulations have regulated the joint ownership installations:
- address criteria
- consumption criteria
The address criteria was originally made, because there was a wish for local connection between the turbine owners and the wind turbines. Thus, there was no political wish, that financially strong individuals were allowed to invest in wind turbines far from their home. Today the address criteria says that, people can buy shares of a wind turbine, which is placed in the municipality where the), live, or in the neighbouring municipality, (it has been changed several times during the last 10 years). The idea reflects that people who live close to the wind turbine, and live with any inconveniences, also shall get any advantages.
The consumption criteria says that, one can only buy wind turbine shares corresponding to 150% of own electricity consumption. Though everybody can own shares corresponding to an annual power production of 9,000 kWh, regardless of the private electricity consumption. Thus it is impossible to speculate in wind turbines, as the possibilities of investments are limited. The regulation is partly introduced, because the turbine owners get the electricity and CO2 tax refunded from the state.
The wind turbine cooperatives are organised as partnerships. This way of organizing has been necessary, because the authorities demand it, if the wind turbine cooperative wants tax exemption. As tax exemption is a condition for the rentability of a wind turbine, this way of organizing is the only one used nowadays. Partnership has the big drawback, that the partners have joint and several liability. This means that each member of the cooperative is personally 100% liable for any debts of the wind turbine cooperative. This has kept many people from participating in a wind turbine cooperative, and does not harmonize with the original Danish cooperative idea.
Private Wind Turbine Economy
The private financial circumstances depend on several factors: installation investment, operation and maintenance costs, annual power production, and payment rates for produced electricity. Typical examples of these costs and income are shown in figure 9.8.
The price of a wind turbine share is often calculated as installation investment divided by annual power production (in MWh).
It can be put like this, the share price is the investment needed when establishing the turbine. to get the annual power production of 1000 kWh. If one wishes to have the costs in DKK/kWh the following figures should be divided by 1000.
Figure 9.8 also shows an example of firs' years account for a wind turbine share, and the simple pay back period, according to two kinds of turbines. The reason why the larger 400 kW turbine has a longer pay back period, can be explained as, this kind of turbine is still new, and therefore not economically optimum yet. Up to now the tendency has been, improved financial conditions for the larger turbines. Within the coming years it is expected that the most profitable turbine size will be about 500 kW.
Many private wind turbine owners have financed their investment by taking a loan. The example shows that the turbine owner will get a small profit of 105 DKK/year per share after repayment on loan.
The key figures in figure 9.8 correspond to the actual financial circumstances, many Danish turbine owners have experienced within the last years. It should be mentioned that single ownership turbines in general have had worse financial circumstances, as well as turbines located at not so windy sites, or overtaken by breakdowns and damages.
The electricity produced by wind turbines in Denmark, should alternatively have been produced by a thermal power plant using fossil fuels, thus polluting with carbon monoxide, sulphur, nitrogen oxides, dust, cinders, etc. Of course energy and resources have been spent to produce the wind turbines, but from then on the wind turbine produces energy without polluting. The energy pay back period is less than half a year for a good located wind turbine (chapter 4). Thus wind power must be characterized as one of the cleanest power production methods today.
However establishment of wind turbines is not totally without environmental impact. Impacts as noise, visual effects, and safety are considered here. The visual impact of wind turbines in the Danish landscape may be seen as an environmental problem. Due to the increasing number of wind turbines in Denmark, this view has often been stated during the last years. This is to a great extent a subjective question, which will not be further discussed here. The safety level of Danish wind turbines are high, and accidents with serious consequences are rare.
The main environmental problem concerning wind turbines is their noise. In Denmark we have environmental legislation, which regulates how much noise a wind turbine is allowed to emit' and which noise level the neighbours must be exposed to. Figure 9.9 shows the noise level around a wind turbine. It shows that a single standing wind turbine can be placed appr. 150 m from the nearest housing, and still keep a maximum noise level of 45 dB(A). For larger estates the noise limit is 40 dB(A), which leads to a minimum distance of 250 m.
The Present Situation for Wind Power in Denmark
It must be said that Denmark is leading in utilization of wind power, and has many years of practical experience with establishment of wind turbines. In other words, we are 5-10 years ahead from the point where the other European countries are starting now. That is why our experiences can support the development in other countries. And if our experiences are used right, other countries might be able to avoid some of the problems we had in Denmark. The fields I feel relevant to address in the following are:
- popular involvement
- conflicts with the established power supply
- planning in the wind power field
- off shore wind turbines
The importance of popular involvement appears from the previous paragraph. As mentioned, the majority of Danish wind turbines are erected by private people. This development has continued in the last years, and will probably also be an important factor in the future. The development has spread dike rings in the water, as existing wind cooperatives have helped new wind projects to get started. This development has been strongly supported by E;nergy Offices and advisers from the Association of Danish Windmill Owners. In other words, it has been possible to lean on a well-developed network of persons and institutions, which have stood together to solve the problems, and force the development. However, there are also tendencies, that the level of popular involvement can not be kept without renewed and continued efforts. The following problems can be mentioned: - it has become more difficult to find a good wind turbine location, without conflicts with landscape considerations, etc.
- long authority hearing hinders new projects
- many interested are already partners in a wind turbine, and new persons, who want to start a wind turbine, become harder to find.
Conflicts with the established energy supply
In spite of a stable development of wind power, the development has always been marked by conflicts with the existing energy supply system. Especially conflicts with the power utilities have influenced the development. Here can be mentioned: payment rates, technical demands on grid-connection of wind turbines, disagreement on how big wind power share can be adopted by the power system, etc. Some of these problems are partly solved through a law adopted in 1992. But not all the conflicts are solved, and the continuing obstacles may unfortunately be expected to reduce the expansion also in the future.
Planning in the wind power field
Until a few years ago only energy planning was relevant according to wind turbines. While the number of wind turbines has increased, physical planning at all levels has been involved. Now counties and municipalities make plans of, where wind turbines can be - and especially can not be placed in Denmark. Different valuations can be made according this development, but in total one can be worried about, if the planning secures installation of enough wind turbines in the future. The official Danish energy plan, E;nergy 2000, assumes that in the year 2000, 10% of the Danish electricity consumption is supplied by wind turbines. This has to be seen in relation to the survey of wind resources in Denmark, which shows that in case wind turbines were installed at all the best wind sites, then we could cover 80% of our electricity consumption by wind energy.
From our point of view the minimum goal is to cover 10% with wind energy. OVE (the Danish Organization for Renewable Energy) has published an action plan on renewable energy, which shows a goal of 25% covering of the electricity consumption.
Off shore wind turbines
In East Denmark, near Vindeby north of Lolland, the first Danish off shore wind farm was established in 1991. The windfarm has been relatively expensive, and belongs to the power utilities. Some wind turbine cooperatives, e.g. Aarhus Bay Wind Turbine Cooperative, have applied for permission to establish off shore wind farms. The project in Aarhus Bay shows good financial conditions (equal to a good inland location), but until now they have not succeeded in getting the permission to start the project. The Ministry of Energy is not interested in, that a private wind turbine cooperative gets involved in off shore wind turbines. This is a block of the development, as we have earlier seen, that good demonstration projects are needed, before a break through is possible.
Small-scale and Stand-alone Windmills
The small household turbines started the development in the 70es. These were later developed to the larger grid-connected wind turbines, and the improvement of the small and not-grid-connected wind turbines more or less stopped. Anyway, in the last years a new interest has appeared in utilizing and developing smaller turbines for alternative purposes.
The various existing types can be parted in:
- small battery charging turbines (0-1 kW)
- smaller wind turbines (1-20 kW), grid connected and stand-alone
- heat producing windmills
- water pumping windmills
- third world applications wind-diesel plants
The two first categories (small battery charging turbines, and small wind turbines rating 1-20 kW) are named household turbines or just small turbines.
The technology of small turbines can be quite simple, demanding little maintenance. Typically the blades are fixed with simple air brakes in the tips, and maybe mounted directly on the generator shaft.
Some of the small wind turbines have a Permanent
Magnet Generator (PMG), and therefore with a simple control are able to produce electricity independent of the grid. The interest in these small turbines has grown, but there is no market for them in Denmark. But some manufacturers sell small turbines. In appendix 3 there is a survey of the small turbines.
The last four types are mentioned to give an overview, but will not be further described.
1. Energihandbogen (The Energy Handbook), Judith Winther et al. OVEs Forlag, 1981.
2. Vedvarende Energi i Danmark (Renewable Energy in Denmark), Jan Viegand et.al. Physical Laboratory 111, DtH, 1990.
3. Wind Power in the 90es - Pure [Energy. FDV, The Association of Danish Windmill Manufacturers, 1991.
4. Information from Annual meeting 1992 in FDV.
5. Wind Energy in Denmark - Research and technological Development. The Danish Energy Agency, 1990.
6. Kortloegning af vindenergi i Danmark (Survey of Wind Energy in Denmark). The Danish Energy Agency and Nellemann Consulting Engineers, 1991.
7. Privatejede vindmollers okonomi (Private-owned Wind Turbine Economy). The Danish Energy Agency, June 1991.
Christian Scholten and Kim Nielsen, Danish Wave Power
A new development on its way, is the development of wave power plants for electricity production. The existing plants are still proto types, but in the foreseeable future waves can cover around 1% of current global energy consumption.
Wave Energy Potential
Sea covers appr. 70% of the earth's surface, and waves contain energy of the order of 90,000 TWh per year, corresponding to an average power of 10 TW, or the current energy consumption of humanity.
With a mean efficiency of 25%, and expecting that only the most suitable localities, which makes up 4% of me resource, will be utilized during the next 50 years, wave energy will be able to cover 1% of the total energy consumption in the foreseeable future, equal to 100 GW mean power.
Wave energy is a renewable energy source. The sun causes winds, and winds cause waves. The wave energy content of a sea varies from place to place. In general it can be said, that the further away from the Equator one is, the more wave energy a sea contains.
Local conditions like e.g. coastal conditions, distances from shores, and debth of the sea, have large influence on the mean wave energy content of a sea area. The wave energy content of a sea area is often stated in kW/m, as the mean power passing a section of 1 m.
The global distribution of annual mean wave energy content in the seas is shown in figure 10.1 as power per m wave front.
The wave energy content in the sea area furthermore varies with the season. In figure 10.2 is shown an example from the North Sea.
Status of Wave Power Development
Research on methods to utilize wave power is being carried out in some places in the world, e.g. in Japan, Ireland, England, Norway, Sweden, and Denmark. There are worked on two main types, installations near the coast, and installations placed on deeper water and several kilometres from land.
The installations near the coast are mainly based on the principle of oscillating water columns, as shown in figure 10.3. A big chamber (like an upturned cup) with an opening to the waves, and with an air turbine mounted towards open air, is built. When the waves put the enclosed air in motion, the air is pressed in and out through the air turbine. This type of plants have been constructed as pilot plants in Japan (in connection to a quay), and in India, England, and Norway.
Denmark, Norway, and Sweden have worked with floats, that are connected to a pump, which is activated, when the waves move the float.
Figure 10.4 shows the Danish system, which is built and tested near Hanstholm. This principle uses a large single acting pump standing on the sea bed. A piston is connected to a float with an elastic wire, and when a wave moves the float, the piston is lifted, and water is drawn through a submerged turbine generator unit, thus producing electricity. When the wave crest has passed, the float is lowered, and the weight of the piston presses the water out through valves.
The Swedes use a hose pump, which is inserted between the float and a large damper disk, which is slack anchored to the seabed. When the waves lift the float, the hose is lengthened, and its volume is reduced. Hereby the water is pressed out and accumulated in a hose, that transport water from several pumps to a joint high pressure water turbine. When the wave lowers the float, the hose turns back to its original volume, and sea water is drawn in through valves.
In Sweden they have researched into a wave rotor, as shown in figure 10.6. It consists of two oblong cylinders, which in principle resemble waterwheels. When a wave is lifted over the cylinder, the enclosed air will turn the wheel, e.g. anti-clockwise. When the wave has lowered, the enclosed water mass will continue to turn the wheel in the same direction, due to gravity.
Still there has only been a few prototype plants running. One of the reasons is, that it is still expensive to secure the installations' reliability and function under the often violent conditions at sea.
Still there is no type of wave generators superior to all others. Some are better to absorb the energy from the waves, others are cheap or more durable. When all is said and done, it is about to construct a machine, which has a competitive kWh-price.
The cost is often defined as:
Aan are the annual costs for interest and repayment of investment debt. As rate of interest is often used the real interest, and as instalment period 25 years. Dan are the annual operation and maintenance costs. ' is the annual mean efficiency of the wave generator.
Pfm is annual mean power of waves per meter wavefront. b is the effective breadth of the wave front, which can be utilized by the wave generator.
Determination of a sea area's annual mean potential
The power per meter wave front of waves with the height H (from crest to trough) can e.g. be written:
p is the density of water in kg/m3,
g is the gravity acceleration in m/sÃ¬
T is the wave period in sec.
This means that Pw - 13 MW/m for the largest waves with H = 30 m and T = 15 sec.
Normal predominant waves have a mean height of 1-2 m, and a period of 5-7 sec. That is a power of 13 kW/m, or only 1/1000 of the power of the largest waves.
In nature waves are irregular and can be described by statistic models.
If the wave conditions are measured, e.g. in 20 minutes, the mean wave height Hm and the significant wave height Hs can be calculated. The significant wave height is defined as the average of the highest 33% of the waves.
It is said, that the waves in this relatively short period are characterized by a sea state Hs Figure 10.7 shows an example of the frequency of the wave heights H for a given sea state Hs.
If the wave heights are measured for 20 minutes every third hour during some years, then the annual distribution of sea states can be found. Figure 10.8 shows an example from ER in the North Sea.
A given sea state Hs contains a power level per meter wave front, which with good approximation can be described by: Pinf ~ 2.05£(Hs)(2.5) (kW/m). In figure 10.9 is shown the variation of Pinf
The wave energy potential in a sea area, e.g. the annual mean potential Pfm, can be calculated by weighting the individual sea states' power Pinf with the matching frequencies, and sum up all the contributions. In figure 10.10 an example from ER is shown, which results from figure 10.8 and 10.9. In this case it appears that sea states around Hs = 3.0 m contribute the most to the annual mean potential.
Wave generators' annual mean of absorbed power
In the efforts to utilize power from the waves, we could easily be led to believe that the optimum would be to aim at a wave generator, which utilized as much as possible of the sea states with the highest contribution to the annual mean power, Pfm. However, this strategy leads to very big plants, that are expensive, as their total capacity in the form of installed power is utilized only a small part of the year.
Wave generators that have the largest energy absorption in small waves, and do not increase the absorption subsequently, often prove to be the most profitable, even though the efficiency is only 1020%.
If the production curve is known for a certain wave generator, this means absorbed power per meter wave front as function of the sea states Hs, then it is possible to calculate the annual mean production and the average annual efficiency of the generator.
Figure 10.11 shows an example of such a production curve for the Danish wave generator. Such a curve can be determined by model tests.
If the absorbed power is weighted with the frequency of the sea states, and these contribution are summed up, it gives annual mean absorbed power, which is 1.65 kW/m for the Danish pointabsorber located at ER in the North Sea. The annual mean efficiency then is:
In the short term it is obviously about testing and developing the principles known today, thus their economy improves to a level, where it gets commercially interesting to construct wave power plants.
In the longer term wave power plants have to be built on very long distances to give a significant contribution to a non-polluting energy supply. If appropriate agreements are made with the fisheries and shipping authorities, such wave power plants are not expected to create severe commercial or environmental inconveniences.
The most energy containing waves occur at coast stretches, which are very scattered populated, e.g. in Australia, Southern Africa, and Southern America. Installations, that are built in these areas, can not be connected to the grid, like in Europe, and any utilization must be combined with long term energy storage in transportable form, e.g. as hydrogen and oxygen. Wave power plants could be producing hydrogen, e.g. by electrolysis of sea water. The hydrogen can be compressed and transported to small power plants based on fuel cells.
1. Energi fran havets vagor (Energy from the waves), Lennart Claeson. Efn-report no. 21, Sweden, 1987.
2. Wave Energy, Tony Lewis. Current Research Activities and Recommendations for European Research Programme. Final Report to DGXII. Cork, Ireland, 1992.
3. Planning a full scale wave power conversion test 1988-89, Kim Nielsen and Christian Scholten. Proceedings of ICOER 89. Hawai, USA, 1989.
Biomass is a local energy source which can relatively easy replace large amounts of fossil fuels for heat and power production. Bio energy is CO2 neutral and therefore a significant factor in the fight against the green house effect.
Lars Helbro, Energy Adviser, Himmerland's Energy Office
Wood has been used as heat source, as long as anybody remembers. And as subsistence on Earth requires a certain amount of vegetation, this possibility will always exist.
During the last years, other crops have become important for energy purposes - e.g. straw, elephant grass, and rape. There are many possible applications, but today they are limited, one of the reasons being that these fuels require more working up than available fossil fuels.
The use of straw for energy purposes is strongly increasing, partly for environmental reasons (according to a political decision it is prohibited to bum straw at the fields), and partly because it is often profitable even with a low efficiency. Wood is used to a less extent, and the wood used is often utilized with very low efficiency.
Today both wood and straw are waste products from corn production and forestry, windbreak belts, etc., - while other biomass products as rapeseed oil, elephant grass, and energy crops, are grown directly for energy purposes and therefore require larger supply of energy before the fuel is ready for use. Growing of bio fuels on large scale may also have adverse consequences, as exhausting of soil and other environmental drawbacks, if it is a monoculture production using pesticides and fertilizers.
Some energy crops may have other functions that save energy during their growth, e.g. as windbreaks or for waste water treatment.
The available annual resources can cover over 15% of Denmark's present energy consumption. With the planned wood planting and a more efficient utilization of both wood and straw, bio fuels are resources that absolutely should be taken seriously.
Vegetation - Combustion
During their growth plants absorb. solar energy, water (H2O), carbon dioxide (CO2), etc., - emit oxygen (O), and form carbon (C),- in the process named photosynthesis.
During the combustion of carbon the process is reversed, as oxygen (O) is absorbed, and heat (solar energy), water (H2O), and carbon dioxide (CO2) are emitted.
The amount of CO2 being absorbed and emitted is exactly the same. Therefore, biomass is a CO2 neutral fuel, wieved over the time span it takes new plants to reach a size that makes them useable as fuel. For straw it is normally less than one year and for ordinary trees about 15 years.
The CO2 relation is the same for oil, coal, and gas, but the time span needed to restore the CO2 balance is several millions years.
By a total combustion of biomass nitrogen oxides (NOX) form, besides CO2, water, and heat. NO: do not origin from the biomass, but from the nitrogen in the air which is consumed by the combustion together with oxygen. This consequently happens in all combustion processes where atmospheric air is added to have oxygen. NOX combine with the moisture in the air and form nitric acid.
The amount of NO' depends on combustion temperature and the amount of surplus air.
The energy content in 1 kg of totally dry wood is appr. 5.2 kWh. In practice it is not possible to dry wood that much. In Denmark wood is considered to have a moisture content of 20% weight of dry wood.
As it takes energy to boil away this water in the combustion process, it is not realistic to count on larger energy content than 4.5 kWh per kg wood. This corresponds to, that 2 kg wood is needed to replace 1 litre of fuel oil, if both are burned with the same efficiency. By increasing moisture content the energy content decreases, until the moisture content is so high that a total combustion is impossible, followed by a drastic decrease of combustion efficiency (see Proper/Improper Combustion).
In Denmark, it is possible to utilize appr. 1.2 mill. tonnes of wood for energy production annually, only half of this is used today and even with a very low efficiency (appr. 30%). The straw potential is about twice as big.
Wood is completely decomposed in a proper combustion. It must be said to be our most environmentally compatible fuel (except hydrogen), as the only pollutants are NOX, which appear from every combustion where atmospheric air is used.
If the combustion, on the other hand, is incomplete then some harmful and malodorous substances appear, which can be of great inconvenience in the local environment. However, they are not comparable to the substances that occur from combustion of oil and coal and may do irreparable harm to the global environment.
The smoke shows, if the combustion is complete. The more black it is, the worse is the combustion. White smoke is not due to bad combustion, it is the moisture vaporized from the wood.
Wood and straw are gas containing fuels, which means they release gasses when burning. Roughly 80% of the energy is in these gasses which have different combustion temperatures. It is a very complicated fuel we are working with. Therefore it is often seen that in fact only part of it bums, while the rest leaves the fireplace as smoke.
A complete combustion of the gasses demands 3 things:
The heaviest gasses do first burn at temperatures around 900›C. This temperature is extremely difficult to achieve near a water or air cooled iron plate, therefore all fireplaces should be masoned.
The moisture in wood/straw needs heat for evaporation,- the more water the more heat is spent on this purpose and the lower the combustion temperature gets. Therefore it might be even more difficult to achieve an efficient combustion.
Creosote (a mixture of condensed water and unburned gasses) occurs easily, if the wood/straw isn't dried properly, as a lower combustion temperature also results in a lower chimney temperature.
Efficient Mixing with Air
As it is very difficult to mix cold air with very hot gasses, it is necessary to preheat the air strongly or to mix air and gasses under strong turbulence.
It must be possible to adjust the air quantity, while too much air will cool the gasses, and too little will be like driving with choke. In practice an air surplus of 100% will usually secure a good mixing.
If the chimney is too low, too leaky, or has too small inner diameter (e.g. because of soot), it will be very difficult to achieve good turbulence.
Space and Time
When temperature and air mixing are all right, the gasses burn. But they need space and time, without decrease of temperature, to burn completely. Therefore it is not enough, that the fireplace is masoned/well-insulated, - there must also be plenty of space for the burning gasses, before the heat is starting to be removed.
The 3 T'es
A good mnemonic rule is that the 3 Tes must be present: Temperature - Turbulence - Time. If just one of these conditions is missing, the combustion will be bad.
The smaller a fire is, the harder it is to achieve an efficient combustion.
In systems with automatic stoking, where chipped fuel is often supplied (e.g. every 30 seconds), it is possible to go down to performances around 5 kW without getting a poor combustion. However, it will not be possible to achieve higher performances than 15 kW in the same system. In slightly bigger (more ordinary) systems the performance is between 10 and 25 kW.
In general it can be put that the larger nominal power the easier it will be to achieve an efficient combustion.
Unfortunately, this is not in harmony with the heat demand of an ordinary single-family house which is 3-4 kW on a standard day in January. It is therefore necessary to be able to store the extra heat for later use.
Both wood and straw can be utilized in district heating systems with automatic stoking.
Straw can be used as bales or chipped, whereas wood can almost solely be used as chips. The boiler efficiency will often be very high, but as the loss in the distribution system is seldom below 20%, district heating systems are not able to compete with efficient individual plants.
In district heating systems the need for storage can be diminished by using several smaller boilers, so the performance can be varied by taking one or more boilers out of operation.
At the Danish market many boiler types are found, which are stated as designed for wood. Unfortunately only a few of them are able to meet the demands that must be considered in order to achieve an efficient combustion.
Amongst the types able to meet the demands, can be mentioned: automatic stokers designed for wood chips; manually stoked boilers for wood that operates after the principle adverse combustion. Boilers of the total combustion type and far the most under-combustion boilers do not achieve as high efficiency.
Automatic stokers are, on the whole, able to run without heat storage, if they are supplemented by solar heating during the summer. All other boiler types will work better and with higher comfort (less to take care of), if they are combined with a suitable heat storage. For the smallest boilers at the market (18-20 kW nominal power) a heat storage of minimum 1200 litres will be appropriate for an ordinary single-family house. Larger boilers need a larger storage, if the goal is one fire a day.
The possible combinations are countless. The ideal will depend on the heating system in the house (radiators, under-floor heating, etc.) and the possibilities for self circulation between boiler, storage, and any hot-water tank.
As straw release the latent gas quicker than wood, it is more difficult to construct a small boiler that in a decent way fulfil the technical demands on combustion, which should be required for resource and environmental reasons. At the same time, straw is at many farms a surplus product which the farmers have problems to get rid of, so efficient utilization does not play an important role as a sales argument. However, still more boilers, often with integrated heat storage tank, can show quite high efficiency (with proportional lower smoke problems and operation need).
Straw pressed to pills can be used in small automatic stokers with high performance.
Other applications for surplus straw gasification, fodder, in district heating plants, etc. will certainly raise the price of straw so boilers with low efficiency will disappear from the market.
Heat storage. In general the same applies to straw burning as to wood boilers, only the nominal boiler performance is mostly larger, therefore the heat store also ought to be larger.
Brick stoves (masoned woodburning stoves) have been used for many generations in Finland and Russia, while they have gained access to other places only recently. This kind of stoves are often preferred in places where they fit the floor plan.
The brick stoves are characterized by combining qualities like high efficiency, minimum operation, good heat comfort (equalized heat supply all day), and high social value as the rallying point of the family.
Correctly designed the daily work will be reduced to one daily fire of 1 to 1.5 hours duration.
In brick stoves the extra heat production is stored in the stone mass. It is more difficult to adjust the store size to the consumption than in boiler systems, as the large stone mass around the fireplace will be able to store more heat, but at the same time releases the heat more slowly to the surroundings.
These stoves are extremely suitable for low energy houses with a reasonable open floor plan. The heat distribution has shown to be much better than for iron stoves and. At the same time, burning of dust in the room is avoided, which may be caused by the high surface temperatures of the iron stoves.
Hot water production in brick stoves has shown realistic without placing water cooled surfaces in the immediate vicinity of the flues (with the risk of condensation). An efficient household installation with very high user comfort may very well consist of a brick stove with hot water production to supplement a solar water heater.
Iron stoves are found in many versions, e.g. in Denmark and Norway, and are produced both in cast iron and sheet iron. Operationally it doesn't matter what kind of iron the stove is made of, but more work has often been done with the combustion technology in the sheet iron stoves. Thus some of these can prove decent efficiencies in a laboratory, but unfortunately often with heat performances that far exceed the actual demand in an ordinary home.
Here the only heat store is the building. Therefore it is important that the house is constructed in heavy materials which can reduce the temperature fluctuation, and that the residents of the house are prepared for stay in the transport way of surplus heat which gives relatively high temperature fluctuations.
The efficiency of wood use depends very much on the user, as an efficient combustion will often supply too much heat according to the actual demand. This is why many people prefer a lower efficiency (more smoke) and a more even heat supply.
It is a paradox that woodburning stoves with a small heating surface - e.g. without cooling of flue gasses - often operate best, with suitable heat emission, and without intense smoke generation. This is mostly due to the fact that the extra heat production from a sufficient combustion disappears through the chimney.
The flue gas temperature measured right before the chimney is often around 300 - 400›C which is far too much for a good burning system. To compare, the outlet temperature from masoned stoves is typically around 120›C.
An integrated water tank, together with a solar water heater, is capable of meeting the hot water demand, at the same time as part of the surplus heat (or unbumed flue gasses) is utilized. However, it is important to place the tank as far from the fire as possible, not to cool it.
Both wood and straw may be used in large thermal power plants.
To avoid unnecessary transport demand, it will often be wise to look at the relation between the local straw/wood production and the energy demand at the same place.
An obvious possibility of generating power in connection with small stoves/boilers is the Stirling Engine (further described in chapter 12) which is characterized by being nearly unaffected by the purity of the fuel and very noise faint.
Gasification of biomass for engines may prove favourable for somewhat larger units (see the text on gasification).
In addition to efficient combustion, easy operation, high security of supply, and low fuel costs, it is also important that the daily user feels responsible for and gets pleasure from functioning of the heating installation.
District heating has a serious drawback here as it will almost always be others fault, if there is no heat, as well as somebody must do something about it, if it appears that the system pollutes.
A family who is often away from home will be best served by an installation which only needs little operation and preferably at optional times. District heating will of course be perfect here, but also boilers with well-designed heat storage tanks can be used.
If the family is at home at regular hours every day, then brick stoves may be the right choice, if the house is suitable for it.
Iron stoves, on the other hand, need more operation, else the room temperature will deviate too much from the desired average. The stoves where it has been successful to lower the performance without compromising too much on efficiency need much care (frequently stoking). Therefore, these are sure to fit best in group families, or families with pensioners, etc.
As starting point ought to be found the solution where the heat production takes place as close to the consumption place as possible and where the operation is as easily seen through as possible, to avoid operation mistakes.
Possible Future Perspectives
As the moisture content of wood is essential for the degree of utilization and contributes often strongly to problems like smoke, chimney fire, tarry soot, etc. when used in households, then development of condensing boilers would better the possibilities for a reasonable utilization of biomass.
People, who already use dry wood (20% moisture), would achieve a reduction in consumption of more than 30%, as also the smoke temperature could be much reduced. Especially for chip burning large savings could be achieved.
The big advantage according these savings should probably not be evaluated so much on economy, as on the reduction in needed store space and workload which certainly will make more people utilize a completely local resource.
Ole Elmose, folk high school teacher, Viborgegnen's Energy- and Environment Office
With the increasing interest in utilizing biomass for energy supply - and preferably for combined heat and power production - gasification calls for renewed interest.
Gasification has been an important part of energy supply earlier; namely at coal gasifications plants wherefrom the gas was distributed through gas pipes and used in gas cookers, and the residue product, coke, was used for heating in solid fuel stoves. During World War II wood by means of a gasifier was used as petrol for cars.
Like this, gasification is not a new phenomenon, but the technology was forgotten for many years because of cheaper and more handy ways of getting energy.
The renewed interest in gasification of biomass, first of all straw and wood/chips, is due to the wish to utilize the residue products from agriculture and forestry, and encourage a more environmental conscious energy use. Here is mainly thought of the CO2 impact in the atmosphere.
As part of the new direction was made a study, at the beginning of 1992, on how far the development of gasifications plants is abroad 11/. A few companies in Europe and North America have developed gasifiers; but the study shows that it is impossible to buy fully automatic and reliable gasifiers designed for cogeneration. Another characteristic of the examined plants is that none of them are capable of utilizing straw, and there is no technology to utilize the waste heat. Up till now the technology development abroad has mainly been directed towards third world applications, where abundant labour is available, and heat production is not that interesting.
So in fact Danish technological development is not in a bad position as Danish straw gasifiers have been developed, both of 1 MW size at Kyndby Power Plant, and in smaller scale, 50 kW, at the Technical University of Denmark. It is especially interesting that it is gasification of straw, as straw is considered to be more difficult to handle than wood/chips utilization
At the moment there are around 100 district heating plants in Denmark using wood (pills, chips, bark) or straw as fuel. Moreover, some communities and institutions - like boarding schools - have started to use wood chips, straw, or wood pills for heat supply; this is a development that is expected to continue in the coming years. Furthermore there are of the order of 14,000 individual straw furnaces, mainly on farms. At last it is estimated that there are appr. 350,000 fireplaces and woodbuming stoves in private homes.
For reasons mentioned in the chapter on planning (chapter 5), it is important to change from heat supply to combined heat and power supply as far as possible. It is in this connection, gasification becomes interesting - as gas can be used in gas engines for combined heat and power production.
If we leave fireplaces and woodburning stoves out of account, there are anyway among the above mentioned heating plants a large market both in number and power for cogeneration plants based on gasification. Concurrently with the development of gasification technology, district heating plants, communities, institutions, and many farms will replace heat supply with combined heat and power supply (cf. chapter 12).
The gasification process is often called thermal gasification, because the biomass is heated in a chamber with controlled air supply. It is important to control the air supply; otherwise, there may easily appear a complete combustion without gas production. During the heating, that usually is part of the process, the volatile gasses, which make up the main part of energy in straw and wood, are liberated. The most interesting part of the gas according to energy are carbon monoxide, hydrogen, and methane. It is a very poor gas (the heating value is lower) compared to natural gas, figure 11.6.
The chemical reactions, the fuel has to undergo before it is gasified, are: drying, pyrolysis, combustion (oxidation), and reduction.
The Countercurrent Gasifier
Figure 11.7 shows a schematic picture of a countercurrent gasifier including the most important reaction zones, temperature levels, main chemical reactions, and flow.
In the combustion (oxidation) zone carbon from the fuel bums and forms carbon dioxide with the oxygen in the air. Heat is emitted during the reaction and the temperature rises until a balance between heat supply and heat loss occurs.
Reaction: C + O2 -> CO2 + Q (393,800 kJ/kmol)
After the oxidation zone the hot gas passes through the reduction zone. There is no free oxygen in this zone which causes that carbon dioxide - an inflammable gas - reacts with the carbon in the fuel and forms carbon monoxide which is a flammable gas. This reaction is endoterm (demands heat) and does not happen before the temperature exceeds 900›C. Carbon monoxide is the most important flammable compound in the produced gas.
C + CO2 + Q (172,600 Kj/kmol) -> 2CO
Another important endoterm reaction in the reduction zone is the reaction of water vapour and carbon to carbon monoxide and hydrogen. The reaction is often called the water gas reaction (known from the old coal gasification plants). Both gasses are flammable, and the heating value of the gas is increased.
C + H2O + Q (13,400 kJ/kmol) ~ CO + H2
During the endoterm reactions the gas temperature decreases and other reactions occur. One of these is the reaction between carbon and water vapour, which forms carbon dioxide and hydrogen.
C + 2H2O + Q (88,000 kJ/kmol) -> CO: + 2H2
If there is a surplus of water in the reduction zone, then carbon monoxide may react with water vapour and form carbon dioxide and hydrogen. This reaction is exoterm (emits heat) and decreases the heating value of the produced gas.
CO + H2O - Q (41,200 kJ/kmol) ~ CO2 + H2
By gasification of biomass, the water content in the fuel is usually that big, that some part of the evaporated water passes through the gasifier and forms part of the outgoing gas flow.
In the pyrolysis zone a thermal decomposition of the fuel is taking place at temperatures over 400›C. Water vapour, methane, tar, etc., are formed in the pyrolysis zone. After the pyrolysis the fuel has changed to charcoal.
In the drying zone in the upper part of the gasifier water is separated from the fuel as water vapour.
The heating value of the gas depends to a great extent on, if the oxygen needed for the gasification is supplied by the air. The nitrogen in the air (appr. 78%) passes through the gas generator and makes up the dominant compound of the produced gas. Another important compound is the water vapour that decreases the heating value of the gas. If very wet fuel is gasified, there is a risk that the produced gas is inflammable.
The countercurrent gasifier has several advantages. First of all it is very simple in its construction and function. Second it is able to gasify a material with relatively high humidity; as the processes in the reduction zone show, water/humidity exactly takes part in the process.
The drawback is that the gas contains a lot of tar which makes it impossible to use the gas directly in engines. Therefore it is necessary to remove the tar - or even better to crack it to flammable substances in order to utilize the energy as good as possible.
Figure 11.8 shows a schematic picture of a parallel gasifier. It is mainly the same chemical reactions in this type of gasifier as described for the countercurrent gasifier.
Unlike the countercurrent gasifier the gas outlet is placed at the bottom of the gasifier and the reduction zone is under the combustion (oxidation) zone. These two modifications cause that tar, etc., which is formed in the pyrolysis zone, has to pass the hot combustion zone before it leaves the gasifier. By this passage the tar takes part in the combustion or is decomposed to light hydrocarbons, and the outgoing gas is under ideal circumstances tar-free. In practice the tar content will be appr. 0.1-0.2 g/Nm .
When using this gasification technology, the gas is directly usable for running engines after soot and ash particles have been washed out. On the other hand the parallel gasifier demands that the biomass do not have too large water content.
A special kind of parallel gasifier has been developed at the Technical University of Denmark. In this, the pyrolysis is separated as a process by itself where for example a cogenerator's exhaust gasses can be used as heating source. This way profit is achieved. But the reason is first of all that the pyrolysis gas can be utilized in the further process taking place in the combustion chamber, in the cavity over the fuel. In this way, the process is optimized and a total combustion and formation of cinders are avoided.
1. Undersogelse af det udenlandske marked for kommercielle troforgasningsanlog til kraftvarmeprodultion (Study of the foreign market of commercial wood gasifications plants for cogeneration). dk-TEKNIK et.al., July 1992.
2. Forgasning - en C(L)EMT - Teknologi (Gasification - a kept (forgotten) Technology), Lars Erik Brath. VEEK- kontakt, no. 10, 1990.
3. Gasgenetorer - sma kraftvarmeanlog med gasgenerator (Gas generators - small cogeneration plants with gas generators). Jesper Schramm and Erik Kofoed, Laboratory for Energy Technology, April 1985.
4. Gengas: Svenska erfarenheter fran aren 193945 (Generator gas: Swedish experiences from 1939-45). Academy of Science, Stockholm 1950.
5. Articles from "Vedvarende Energi og Miljo" (Renewable Energy and Environment) and "Energi og Planlogning" (Energy and Planning).
Ole Skadborg, Viborgegnen's Energy and Environment Office Ann Vikkelso, Copenhagen Environment and Energy Office
Biogas technology was introduced in the last century; first of all as a sanitary measure, as well as for reduction of volume and smell of the increasing amount of garbage from the growing cities. A real utilization of biogas was only introduced in this century.
Today biogas plants gain prevalence all over the world as a method for energy production and recycling of nutrients for cultivation of plants. The sources are farmyard manure, plants, remains of plants, and organic waste from industry and households.
Today, there are two types of plants in Denmark; farm plants and joint plants. The farm plants have the advantage that long-distance transport of liquid manure is avoided. On the other hand it may be a problem, that more energy is produced than used a« the farm. An advantage of the joint plants is, they can be located close to an urban area and supply district heating.
Biological process and products
In the biogas process high-molecular organic material is cracked to low-molecular, inorganic substances and gas by means of anaerobic (oxygen free) bacteria:
Biomass + Bacteria -> Gasses + Nutrients
CHO (N,P,K,S..) -> CH4, CO2,N..+ N,P,K,S..
The decomposition more or less corresponds to the processes which take place in the nature, but with the difference that the natural processes mainly take place by presence of oxygen (are aerobic). Therefore the intermediate products of the processes are different, as well as the chemical composition of the end products.
In traditional Danish agriculture the alternative of using farmyard manure for biogas production is to put it on the fields where it decomposes in an aerobic process. This process goes off slowly, and nutrients (e.g. nitrogen) risk being washed out before the plants manage to absorb them. Likewise, the energy potential of the biomass is not being utilized.
In a biogas plant the biomass is converted into methane, for instance, which is collected and utilized for energy production. In this way, imported fossil fuels are replaced, Danish currency is saved, and air pollution decreases. The degassed biomass (bio sludge, or liquid and solid manure) with a great part of the nutrients on mineral form can easily be utilized in traditional agriculture, as it is very similar to artificial fertilizer. At the same time, the degassed manure is provided with some positive elements compared to untreated farmyard manure, figure 11.9. As less nutrients are lost than by traditional treatment of manure, the consumption of artificial fertilizer is decreased.
Some organic and biodynamic farmers are very sceptical towards biogas. The problem is that a larger part of the nutrients are mineralized after the biogas process. Because bio sludge is so similar to artificial fertilizer with the nutrients on an easy accessible form, the plants are forced to absorb more nutrients and absorb them faster than, when nutrients are slowly liberated due to natural (aerobic) decomposition of organic matter at the field. This generates plants that are less healthy and more sensible to diseases, etc. The problem with nutrients being washed out is in general much smaller at organic farms, as they are more careful when manuring than in traditional agriculture where farmyard manure is often seen as a waste product.
Anyway, this is a longer discussion, and we will not go into details here. But there is no doubt that other biogas systems must be developed, if biogas production shall be suitable for organic farming.
The Biogas Process
In a biogas plant the biomass is heated up to the process temperature in an air tight reactor and a sufficient process period is secured. The usual process temperatures are either in the area (30-40›C) or thermophile area (50-60›C) and with 10-20 days stay in the reactor. The process is quicker at high temperature, that is why the staying period and the reactor volume can be decreased. On the other hand, the demands for process control and heat recovery are larger with high process temperature.
Today the thermophile process is considered to be easy to control, and projects that are big enough to include investment in heat recovery are mostly based on the thermophile process, the highest hygienic standard is also achieved like that. Especially when handling human waste, as kitchen waste and waste water, that later will be used as fertilizer, a high hygienic standard is demanded by the veterinary authorities. This can be achieved by securing that the material is 55 ›C for at least 4 hours or 70›C for 1 hour.
The biogas formed in the process is a mixed gas consisting of 60-70% CH4 (methane), 30-40% CO2 (carbon dioxide), 0-1% H2S (hydrogen sulphide), as well as traces of H2 (hydrogen) and N2 (nitrogen). The inflammable part is methane that has a heating value of 10 kWh per mÃ¬ CH4. This means that biogas has a heating value of 6-7 kWh per mÃ¬ biogas.
Design of Biogas Plants
A biogas plant consists of:
* Pre-storage tanks (receiving unit) where farmyard manure and other biomass products are mixed before being pumped to the process tank (digester)
* Reactors where the process takes place and the heated biomass is degassed
* any special sanitation tanks
* Manure tanks, where the degassed liquid manure can be stored until manuring the fields
* Any gas storage
* Gas furnace or cogeneration plant
Figure 11.10 shows the design of a biogas plant, in this case a joint biogas plant with separate receiving unit. It receives solid and liquid farmyard manure from several farms and various other biomass products that are mixed and pumped to a pre-storage tank. At smaller (farm) biogas plants the receiving unit is normally reduced to a prestorage tank, for the rest the principle design is the same.
The biogas is utilized in gas boilers or cogeneration plants. Figure 11.11 shows the principle of a gas-fired cogeneration plant.
The biogas production in agriculture is based on farmyard manure which is nowadays often supplemented with other biomass to optimize the biogas production and profit. The supplement increases the content of nutrients and in some cases generates profit from receiving organic waste products. This waste would cost the producers more to get rid of in another way, e.g. at deposits.
The biogas potential in farmyard manure with a dry matter content (TS) of 5 % are of the order of
0.2-0.3 m CH4/kg VS (volatile organic dry matter) or 100-150 kWh per tonnes liquid manure. The potential depends on how the animals are fed and how they digest the food, in addition to the dry matter content. Therefore the variation is very big. In general the following normative figures for biogas potential in manure from different animals can be used:
1 cow (500 kg)
1 sow (150 kg)
10 porkers (60 kg each)
Many other kinds of biomass both have a higher content of organic dry matter than farmyard manure, which for liquid manure is 3-6%, and higher energy potential of the dry matter, figure 11.12.
Farm Biogas Plants
The first agricultural biogas plants that were built in Denmark, were individual farm plants with vertical or horizontal reactors. There was no development for some years, but the development of cheap standardized farm biogas plants has started again, and during the last years several new plants have been built, figure 11.13.
Today work is going on to make manure tanks into low-temperature biogas plants by equipping the tanks with heating and establish a membrane covering (soft-top) under which gasses are collected, figure 11.15.
Joint biogas plant
1. Reception building.
2. Prestorage tanks, 1069 m each.
3/6. Heat exchanger.
4. Digesters (reactors), 3 pcs, 2600 m each.
5. After-sanitation channel.
7. Chips. Delivery and burning.
Heats manure to 55›C.
8. Storage tanks, 1560 m each.
During the last years special efforts have been made to build and test centralized joint biogas plants where the farmyard manure from several farms is transported by slurry tankers to centralized treatment together with other kinds of organic materials. The degassed manure is brought back to the manure tanks at the farms or to new-built storage tanks at places where the manure will be utilized, again by a slurry tanker.
In Denmark, there have been built 10 joint biogas plants of different sizes where continuous registration of operation and production results are made. Registration is also made on 9 of the farm plants.
As and alternative to the existing plants, Viborgegnen's Energy and Environment Office works on predesigning plants where transport of manure by slurry tankers is replaced by pumping.
Establishment of biogas projects includes more questions than this article could cover. But through the experiences yielded in Denmark good expertise in the biogas field is established. And the earlier scepticism towards biogas plants has turned into a growing interest, not least because of the enhanced and documented operation and production results (figure 11.18).
Ole Elmose, Vibrogegnen's Energy and Environment Office
Decentralized combined heat and power production - cogeneration- is a very flexible and efficient way of utilizing fuels. Cogeneration based on biomass is environmentally friendly, and all kinds of biomass resources can be used.
The role combined heat and power production plays in Danish energy supply originates from the decision in 1978 to establish a national natural gas grid (see chapter 53. At present the natural gas system is one factor blocking the utilization of biomass and natural gas in decentralized cogeneration plants, because a great part of the heat market is lost for decentralized cogeneration due to the individual gas supply.
In June 1986 it was decided that 450 MW decentralized heat and power plants should be established. These are very efficient and environmentally compatible, if they are based on natural gas or biomass. The interest in biomass as basis for combined heat and power production is caused partly by environmental considerations, and partly by the desire in agriculture and forestry to get rid of an increasing surplus of residue products, typically straw and wood chips.
But exceeding the problem with an insufficient heat market, the energy policy has caused that until now there has been no sufficiently purposeful and ambitious aiming at the cogeneration technologies, that first of all shall lead to an increased use of biomass in heat and power supply.
Cogeneration - why ?
For reasons mentioned above and in the chapter on energy planning there is a large political interest in changing the local heat supply to combined heat and power supply - this means cogeneration of heat and power.
It is a fundamental physical condition that not all latent energy of a fuel can be converted into tractive power, e.g. to run a car. The main part of the energy is necessarily transformed to waste heat which in the car example disappears by motor cooling and with the exhaust.
Cogeneration plants can be used in all situations where a given heat demand exists. This include all together an extremely large number of district heating plants, institutions, co-operative building societies, industries, etc.
For the cogeneration technologies described in this chapter the primary interest is due to, that a very large percentage of the fuel's energy content is utilized, typically 85-95%. This must be compared to the relatively low energy efficiency of centralized thermal power plants, the annual mean efficiency is about 55% in the El,SAM area (Jutland, Funen).
Another important reason for the interest in decentralized cogeneration is the possibility to utilize renewable bio fuels straw, wood, manure, etc. There are furthermore a few circumstances which are not that much noticed in the political debate.
First of all a large number of cogeneration plants increase the security of power supply. It is not usual that the large power units break down, but it happens. It is obvious that the consequences of missing a large unit are much more significant, than if it is one of the much smaller cogeneration plants.
Second there is a considerable energy loss from the power grid. In the ELSAM area it is good 7% in average. But this figure covers very large variations through the day, and furthermore depends very much on the voltage level. Thus the energy loss from the low-voltage grid is much larger than from the high-voltage grid. All in all this means that e.g. on a winter day at 5 pm there is a large energy loss from the low-voltage grid.
Exactly because many of the cogeneration plants are coupled on the low-voltage grid, they also reduce the grid loss which influence the overall energy efficiency.
The most common type of combined heat and power production in Denmark is connected to gas-fired internal combustion engines which is a well-known technology. They can be found on the market at sizes from 7 kWpower to about 4 MWpower, and the power efficiency is good 20% for the small engines and over 40% for the largest. As power production is viewed as the main purpose, it is important that the power efficiency is continuously increased.
The lower limit for a profitable cogeneration plant is a heat demand of 15,000 m natural gas per year and a power consumption of 50,000 kWh per year with the current engines at the market.
The gas engine fuel is mainly natural gas and it will remain like this for several years. A few plants are based on biogas which will gain increased utilization, while various types of biogas plants are developed and established.
It is assumed that gas from thermal gasification of straw and wood (see chapter 11) will also spread as fuel for stationary cogeneration plants during the coming years.
There are some differences between cogeneration plants according to operation strategy. The larger plants, typically connected to a district heating plant or an industrial company, are mainly in operation during daytime at weekdays. It is because the payment for power is most favourable at that time, which again is due to that the capacity is paid for during the periods with high consumption. In these cases the cogeneration plant produces heat both for covering the actual consumption and for storage in large water storages. The storages are then emptied for heat at night and during the weekend. It is a political request that 90% of the annual heat consumption must be supplied from the engine, the rest is supplied by a gas boiler.
This operation strategy is only realistic when using natural gas as fuel, as there is enough at a certain time. Contrary to continuously gas production from a biogas or gasification plant. On the other hand the demand for a variable power production will increase, when cogeneration plants with variable production are established.
The smaller plants are typically base load plants that operate day and night. They supply power to own installations and cover the power consumption. In this case the plant has 2 power meters; one that registers buy from the power utility when the consumption exceeds the production, and another that registers sale when own consumption is less than the actual production.
This type of cogeneration plants has severe environmental and resource advantages.
Natural gas is the least polluting of the fossil fuels. It is partly due to the relatively high hydrogen content that becomes water in the combustion. The CO2 emission from natural gas is therefore smaller than from oil and coal.
The NOX pollution from the engines are reduced according to authorities' demand by mounting a 3-way catalyzer or - more often - by using low-NOx engines (lean burn). The smallest engines are excepted from these requirements.
According to resources, the advantage is as already mentioned a higher energy efficiency than at centralized thermal power plants.
Some larger district heating plants have based their heat and power production on gas turbines. They can be regulated less than gas engines, and as they by mean of their size presuppose a large heat demand there will not be space for many new in the future. There are simply not that many cities with a sufficiently large heat demand. Apparently there is neither any product development taking place to increase the power efficiency, as it is the case for gas engines.
Combined heat and power production based on steam
The Danish effort to increase the use of biomass mainly straw and wood - as fuel in combined heat and power production, increasingly draws the attention towards steam engines and steam turbines.
The steam engine is a well-known technology, but for different reasons it hasn't been developed for several years. One of the problems has been the contact between lubricating oil and steam. This problem has been solved with a new design of the steam generator which is manufactured in Denmark and is just ready for the market.
The advantage of this cogeneration technology is that biomass can be combusted directly in the steam boiler and obtain the wanted steam pressure of 20-30 bar.
The disadvantage is that power efficiency will hardly exceed 15%. Therefore it is a question if the steam engine is able to compete with cogeneration based on gasified biomass in the longer term.
There seem to be better possibilities for steam turbines with a combination of direct stoking of biomass in the boiler, and superheating of the steam with natural gas. A Danish district heating plant is preparing a test plant based on this technology. Its advantage is a significantly higher power efficiency than the steam engine.
The Stirling Engine
The Stirling engine is a hot-air engine, named after the Scottish priest Stirling who invented it in 1817. Since then it has been designed and manufactured in a vast number of designs.
In spite of intensive and expensive research it is nearly without importance, as the research has been aimed at developing a car engine, which it is not suitable for.
On the other hand there are large perspectives in viewing it as a stationary combined heat and power plant. There is a growing understanding of this that has resulted in new research and production aimed at this. About 150 pieces have been made in batch production in India. This is a simple low-pressure design with a power efficiency of about 10%.
The Stirling engine has many advantages. In principle it is a very simple technology - also in the advanced version with helium instead of air and high mean pressure. Furthermore a big variety of fuels can be used, including concentrated solar heat and clean exhaust from e.g. a gas engine. With the materials used today, it demands about 700›C as optimum working temperature. And the hot air must be that clean, that coating does not occur at the heating surface. Finally, it is nearly noiseless and probably very stable in operation.
The description of the Stirling engine is to a high degree based on the research carried out at the Technical University of Denmark. A 10 kWpower model with helium as medium and a mean pressure of 50 bar has been tested in summer 1992. The results are very promising and it is specially interesting that the power efficiency of this engine is about 30%.
The perspective of heat and power production based on the Stirling engine is that it can probably be produced in a range of 1 kWpower to 150 kWpower in the nearby future; in the longer term maybe with an even higher output.
Such small cogeneration units can give the Stirling engine a tremendous distribution and have a revolutionary influence on our energy supply.
Manufacturers Association Erik Dahl, Industrifilter Stavnagervej 5-7, 8250 Egaa ph +45-8622 2900
The Danish Agricultural Advisory Centre Straw Committee Udk'rsvej 15, Skejby, 8200 Arhus N ph +45-8610 9088
Danish Straw Suppliers Agerupvej 120, 4140 Borup ph +45-5362 5292
Institute of Agricultural Economics Gl. Koge -Landevej 13, 2500 Valby ph +45-3644 2080
Centre of Biomass Technology:
Danish Technological Institute Teknologiparken, 8000 Arhus C ph +45 8614 2400
Danish Boiler Owner's Association dk-Teknik, Gladsaxe Mollevej 15, 2860 Soborg ph +45-3969 6511
National Agricultural Engineering Institute Bygholm, 8700 Horsens ph +45-7562 3199
Danish District Heating Association, Straw Dept. Galgebjergve; 44, 6000 Kolding ph +45-7552 8811
The Biomass Group Kronprinsensgade 6A, 1114 Kobenhavn K ph +45-3393 2820
BWSC A/S Postbox 235, 3450 Allerod ph +45-4814 0022, fax +45-4814 0150
Jysk Biogas A/S Trendavej 10, 9640 Farso ph +45-9867 8489, fax +45-9867 8711
Kruger-Bigadan A/S Gladsaxevej 372, 2860 Soborg ph +45-3167 4466, fax +45-3966 2022
Kruger-Bigadan A/S Industrivej 4, 5380 Nr. Aby ph +45-6442 3180, fax +45-6442 2614
Bioplan Aps Livovej 8B, 8800 Viborg ph +45-8661 3833, fax +45-8662 6836
Bioscan A/S Orbaekvej 101, 5220 Odense S0 ph +45-6615 4143, fax +45-6615 4743
B&S Energiteknil; Bredgade 56, 7400 Herning ph +45-9712 4633, fax +45-9722 4425
Carl Bro A/S Granskoven 6, 2600 Glostrup ph +45-4296 8011, fax +45-4296 0055
Hedeselskabet, P.O.Box 110, 8800 Viborg ph +45-8667 6111, fax +45-8667 1517
Nelleman A/S Vestre Kongevej 4-6, 8260 Viby J ph +45-8614 7111, fax +45-8614 0088
PlanEnergi Jyllandsgade 44, 9520 Skprping ph +45-9839 2400, fax +45-9839 2498
Ramboll, Hannemann & Hojlund A/S Goteborg All' 12, 8200 Arhus N ph +45 8616 2244, fax +45-8616 2388
1 Joule (J) = 1 Watt*Second = 278*10-6 watt*hours (Wh)
1 Wh = 3600 1
1 cal = 4.18 1
1 BTU = 1055 J
1 kilowatt*hour/year (kWh/year) = 0.114 watt (W)
1 PJ = 278 GWh =
1 GJ = 278 kWh =
1 TWh = 3.6 PJ
1 kWh = 3.6 MJ
Latent Heat (approx.)
= 10 kWh/litre
1 Toe (tonne oil equivalent) = 1.16 m oil 1 barrel of oil = 159 litre of oil 1 barrel oil per day is equivalent to approx. 50 tonnes oil per year.
Emissions in tonne per PJ
Fuel SO2 NOX as NO2 CO2