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close this bookBoiling Point No. 38 : Household Energy in High Cold Regions (ITDG - ITDG, 1997, 40 p.)
close this folderGTZ News: Non-theme articles
View the document(introduction...)
View the documentImproved institutional stoves for Sudan schools
View the documentHaiti: Cooking stoves and domestic energy
View the documentHousehold energy in a recently electrified rural settlement in Mpumalanga, South Africa
View the documentImproved Tunisian domestic bread ovens: Flying saucer lids save 50 per cent fuelwood
View the documentMumu: A traditional method of slow cooking in Papua New Guinea
View the documentReducing the risks of poisonous emissions from stoves
View the documentUpdate on biogas in Nepal
View the documentResearch and development


Household Energy Programme (HEP) - Co-ordination and Advisory Service, PO Box 5180, 65726 Eschborn, Germany, Tel: 6196 793004-7, Fax: 797325
Editor: Cornelia Sepp

News from Headquarters

Staff Announcements

Dr. Petra Wagner, formerly assistant team leader, has left the HEP-team after three years of successful cooperation. She will continue to work for GTZ, but will be in charge of the preparation of the EXPO 2000 World Exhibition in Hanover as of January 1997. Two new staff members will join the HEP-team at headquarters: Birgit Starkenberg will take up responsibility in February 1997 for project control, contracts and household energy in Uganda and Anke Weymann will be in charge of all projects within French speaking countries.

Trudy Konemund has been appointed team leader for the new project 'Biomass Use and Household Energy in Ethiopia' which focuses on the integration of household energy measures into national sector programmes for resource conservation and health. Vivienne Abbott will be engaged as technical advisor in that same project.

Sahel Regional Bureau

The regional HEP bureau, PED-Sahel, with Beatrix Westhoff as regional co-ordinator has been established in Burkina Faso. The contact address is:

Programme Energie Domestique (PED) Sahel
01 B.P. 1485, Ouagadougou
Burkina Faso
Tel.: 00 226 - 36 30 09
Fax: 00 226 - 31 74 73 email: [email protected]

Open House at GTZ/HEP Headquarters

HEP acknowledges the importance of public relations, extensions services, and sensation activities in developing as well as developed countries. Thus, an open house event was held at GTZ in Eschborn in June 1996, presenting an exhibition and slide show focusing on household energy and household energy projects.

Integration of a Household Energy Component into the Gambian German Forestry Project (GGFP)

During a two week mission to The Gambia in June 1996, the possibilities for including household energy measures in the community forestry approach of the Gambian German Forestry Project (GGFP) were examined. It was found that favourable conditions for an integrated approach exist. Also, on account of previous stove dissemination efforts, a basic knowledge of stove technology is already widespread in the country. Because established field structures, dissemination strategies and trained extension personnel are available, household energy can be a part of the bigger theme of natural resource management. The effects of working together with community forestry are seen in the support of awareness raising, the facilitation of women's participation in forestry committees, and the strengthening of the self-help approach. The household energy measures will create much-needed immediate or short-term benefits for the population, whereas the beneficial impact of most community forestry activities will occur only at mid-term. It was suggested that household energy sensitisation strategies should be integrated into all steps of the community forestry approach, and the establishment of any parallel structures should be avoided.

Household energy as a school subject

The 'Projet Foyers Ameliores (PFA)' in Bamako, Mali, by Dagmar Orth

People are aware that their natural environment has changed. Vegetation has become much more sparse. Environmental education stresses the links between environmental degradation and energy use. introducing the topic of household energy to pupils in schools is one way of awareness raising.

The household energy project in Mali, Bamako, 'Projet Foyers Ameliores (PFA)' has taken educational needs seriously. The project's extension workers have been working with school children aged 12 - 14 in Bamako since 1990, disseminating their knowledge of improved stoves. These activities were not integrated into the school curriculum previously, but took place in a more or less spontaneous way, depending on the extension workers' visits. It soon became obvious that to spread the activities in a co-ordinated and permanent way, they would have to be made a fixed item in the curriculum. Teachers, and not the project's extension workers, should teach this subject in school.

Since 1995, in co-operation with the Ministry of Basic Education, the 'Institut Pedagogique National' and several other projects working in the field of basic education, the PFA initiated the process of integrating household energy into the curriculum. Links between the subject and existing courses were established, for example in geography, home economics, and languages. A further activity was the participation by the PFA in a work-group concerned with the development of a broader-based course in environmental education.

The procedure for developing such a curriculum is a long and trying one, so as well as working with the formal education sector, the PFA collaborated with NGOs active in the informal education sector, especially UNICEF. In both sectors, the PFA participated in the ongoing training of teachers. In the formal education sector, the project taught trainers for teachers at the two teacher training institutes.

The material developed by the PFA includes:

· a concept for awareness-raising and training for teachers and teacher trainers,
· a specimin lesson for awareness raising of secondary school pupils, and
· a series of lessons for primary school children.

As long as household energy is not integrated into the official curriculum, PFA team members discuss the possibilities of integrating the subject into existing courses with the teachers. The specimin lesson for secondary school pupils and the concepts are presented to them. Where necessary, teachers are trained in building the improved clay stove 'Nafama'. in this case, the PFA staff emphasises the fact that pupils are not expected to be expert stove-builders.

The course on improved stoves places the subject in the wider frame of environmental protection and measures to prevent desertification. It relates pupils' knowledge of desertification to the theme of improved stoves as pan of a basic secondary school geography lesson,

The two pictures illustrate the link between environmental degradation and energy needs. Pupils are encouraged to see improved stoves as one way among others to provide a solution to this problem (Figures 1 and 2).

The series of lessons for the primary schools is conducted in two ways: by practical excursions And by lessons in the classroom. The pupils not only come into contact with the various types of stoves, but they also team to recognise the effects caused by people satisfying their basic needs in a fragile environment.

The experience in Mali was a positive one on several levels. Policy makers in the education sector were already aware of the problem. Teachers welcomed our input and information and the pupils were interested and understood the broader context.

Of course, the influence which younger school children have on their families is not direct or obvious, but older pupils transferred their new knowledge to their families. It is our hope that they will also transfer their new understanding into the families they will start later.

Although the effects of the activities cannot be measured at present - for example by an increase of stoves sold right now - they are a pioneer investment for the future.

Overall, a close and intense co-operation between household energy ventures and basic education would be desirable and an official integration of household energy ideas into the school curriculum should be envisaged for the future.


The Rational Energy Supply, Conservation, Utilisation, and Education Project. in Dadaad Division. Kenya

The arid and semi-arid lands of Dadaab division in north-eastern Kenya play host to thousands of refugees who entered the country during the early 1990s. Following a decision by the United Nations High Commission for Refugees (UNHCR) three refugee camps for roughly 120,000 people, mainly from Somalia, were established.

The area is poor, barely supporting the nomadic people native to the region. As a consequence, environmental degradation in and around the camps has increased, as the additional demand for firewood, poles, and grass has had to be satisfied from nearby natural resources.

The Rational Energy Supply, Conservation, Utilisation, and Education Project, in short RESCUE, commenced operations during 1993 with a view to easing the household energy and environment related problems. During its first year, RESCUE focused on start-off activities, infrastructure development and logistical support, with full scale implementation of planned activities not starting until the second year. These included improving extension strategy and messages, demonstrating ways of restoring the environment, and reforestation measures. Wood fuel saving gooks and user-constructed Rhoda stoves were disseminated in exchange for either work done or tree seedlings planted, with greater importance placed on the latter. Measures to make people aware of the problems covered 80 per cent of the refugee households.

In January 1996, RESCUE entered into its second phase, which is expected to run until December 1998. There has been a significant change in the project's focus of activities, namely an intensification of environmental protection measures and the active involvement and participation of the local host communities and the refugees. Whereas the first phase was aimed at quick results and relief through stove dissemination and propagation of energy saving methods (during the first year malnutrition occurred and the project was in an emergency situation), the second phase adopts a sustainable development approach and centres on the rehabilitation and conservation of the environment.

The main emphasis is placed on the refugee and host communities working together. This is a logical step as these refugee camps are 'consolidation camps' which will continue to exist and will absorb remnants of refugees from other camps scheduled to be closed.

The project has to cope with a number of rather tricky tasks. The most important one is that refugees who view themselves as passers-by must be convinced that investment of labour and effort in environmental protection measures is worthwhile. In addition, mechanisms have to be developed for the host communities and the refugees to work together. Finally, systems need to be developed and promoted for appropriate natural resource management. Ultimately, the participation of the population in natural resource management needs to be assured and incentives for the rehabilitation and conservation of the natural resource base must be provided, especially for the refugees.

RESCUE is facing a number of challenges and it will be interesting to experience its transformation process from a relief/emergency project to a sustainable development project.

Challenges of disseminating stoves in a refugee situation

by Amina Abdalla, GTZ RESCUE Kenya

In most humanitarian relief situations, agencies concentrate on providing the victims with food, shelter, clean water and medical care. Environmental issues in refugees situations were until recently not adequately covered. Often it is assumed that standing fuel stock around the camps is sufficient to meet the need of the displaced. Energy conservation training and dissemination of improved stoves remain the most widely used intervention measures to address refugee impact on the environment. Nevertheless, only small and decreasing budgets are made available to household and institutional energy conservation programmes (Kimani 1995).

Short term concerns frequently take priority over environmental rehabilitation. In the case of refugees, successful stove dissemination is even more challenging, as the planning horizons are short-term and the people are thus less motivated or even reluctant to invest in environmental protection measures.

Stove dissemination:

Stove dissemination projects in conventional development have, over time, learnt that free distribution of stoves and lack of energy conservation training are the major causes for non-sustainability. The fact that refugees are poor and understandably use their meagre budget to supplement items missing in their food baskets necessitates the exploration of refugee resources other than money in stove dissemination. Tree planting and provision of labour for environmental rehabilitation work are some of the exchange commodities tested with positive results.

The lessons learnt through the use of environmental based exchange commodities include (amongst others): the need to introduce a self made stove model, to ensure that acceptability of the stove dissemination strategy is not due to lack of opportunities for refugee labour; to integrate stove dissemination programmes into wider non-seasonally based activities that can ensure continued availability of work, as opposed to environmental rehabilitation work, which is seasonal.

Capacity building:

Linking stove dissemination to energy conservation training

In a refugee setting, where the benefit of any programme is measured by a quantitative approach, the development of energy conservation training is under more strain. The need for training is even higher when the refugee community has experienced little or no fuel shortage in its home country.

Depending on the education level and conservation skills of the community an effective trainer to trainee ratio needs to be decided. The initial ratio needs to be as high as possible to ensure quality information in the beginning and thus avoid possible distortion caused by the healthy refugee rumour machinery.

Simpler energy technologies, that involve participation in design and construction, facilitate the development of the training component. Technologies that involve one to one training as a precondition have higher utilisation patterns.

Stove Production:

Achieving sustainability in stove production through commercialisation

Transport costs and damage to stoves during transportation make the supply of prefabricated stoves to remote refugee camps a costly and unsustainable venture. The question of local fabrication soon becomes essential. We again learn from conventional stove programmes that sustainability in stove production is best achieved through commercialisation. The problem lies with the high stove requirements and short delivery period characteristic of refugee situations.

The prospects for local fabrication is determined by the number of artisans available and whether they are effectively motivated. Motivation can best be achieved through training, offering competitive prices for products, and most importantly, facilitating the supply of quality production tools. A non-subsidised approach needs to be employed, since it results in a cost effective and self sustaining process.


Although many professionals argue that exchange commodities (e.g. stove for work, stove for tress) are a reward punishment approach, it remains the most effective channel through which refugees can be motivated to engage in unpopular activities. It is, however, important that training on proper utilisation of stoves and accompanying energy conservation training precede the dissemination of exchange commodity-based energy saving technologies. Local production of improved stoves at a non-individual level needs to take into account post refugee markets and a sustainable handing over process.

Improved institutional stoves for Sudan schools

by Mohammed E. Abdelrazing: Sudan Ireland Development Co-operation Program, Rufaa, Sudan


The total consumption of wood in the Sudan during 1994 was estimated as 16 million cubic metres, 90% of which was by the household sector (14 million cubic metres).

The efficiency of the traditional stove used in Sudan was estimated to be 12% so more efficient stoves could save thousands of feddans (acres) of forests.

The El Nabti Quranic School has an improved stove which cooks for 1000 students. The main dish for the three daily meals is asida, a thick porridge made from sorghum. This dish is similar to the Kenyan I Ugali and Zimbabwean Sasda. The food is cooked in large pans with curved bottoms. This causes high heat losses when a three stone fire is used. The new stove saves two cubic metres of wood per day.

In Rufaa secondary school in North Sudan (300 students), three charcoal stoves were built to replace the traditional stoves which consumed three bags per day (40kg bag) of charcoal. Using the new stoves, the consumption dropped to half a bag daily. The new stoves saved charcoal, reduced overall cooking times by five hours and retained enough stored heat to keep the food warm till supper (see Figure 1).

The stoves can be used inside the kitchen or out of doors, but the chimney should always be outside the kitchen. The site of the stove should be in a safe, clean and convenient place where disturbance by the wind is slight.

There are two main types of cooking pots which are usually used in Sudan; cylindrical pots with capacity from forty to eighty litters which are made of aluminum and imported: and pots with curved bases with capacities from 80 to 250 litres. These pots are manufactured in Sudan by blacksmiths and they use heavy gauge 1.5-3mm sheet.

In prisons the stove is used for making a sort of pancake from sorghum on a flat rectangular heavy gauge plate. In oil factories, the boiler shape is square or rectangular.

Improved woodstove

General Construction

The firewood stove is constructed of bricks and mortar and it is not more than 0.8 metres high. It has a chimney to produce draught for combustion and to remove the smoke from the kitchen, assisted with a bottle for blocking flue gas. There are two inlets, the upper one through which the fuel is fed and the bottom one to draw the preheated air into the chamber. The fuel inlet has a door to control the entry of cold air.

The method for constructing the stoves is always the same. The shape of the pot holes in the top of the stove is dictated by the shape of the cooking pot, which is usually round, but in the case of the soap factory shown in Figure 2, rectangular containers are used for the oils used in soap manufacture.

Internal Construction:

The grate is made from steel reinforcing rods, 12 or 16mm in diameter with 12-14mm spacing The gaps allow sufficient air to get in and the ash to fall through. To ensure good combustion and heat transfer, the distance from the fuel bed to the pan bottom is critical.

The pot should be a good fit in the hole in the top of the combustion chamber in order to make a seal and ensure that the hot gases go through the passage to the chimney. The small gap between the vertical wall of the combustion chamber and the pot sides is designed to suit the pot to be used so as to give maximum heat transfer.

The passage to take the hot gases from the combustion chamber to the chimney must be the right size and shape, lead up to the chimney and must be kept clear of ash and debris.

The charcoal stove

The four main differences between the charcoal stove and the wood stove are:

· The absence of a chimney in the charcoal stove (see Figure 4);

· The grate is a punched metal sheet instead of the steel bars in the firewood stove;

· The channel between the stove walls and the pot sides must be wide enough to allow the hot gases to escape at the top whilst giving maximum heat transfer to the pot [normally 3-8mm, ed.]

· There are inlets for secondary air.

There have been no laboratory tests carried out to determine the efficiency of the stove, but according to users, the fuel saving is 60-80%.

The stoves have an expected life of more than two years, if they are well constructed and maintained regularly.

Figure 3. Woodfuel burning stove for institutions


Door for In Let of Feeding Fuel


Metal Sheet


Air In Let





Reinforcing Bar


Stove Body


Brick and Clay


Inlet for Feeding Fuel



Door for Cleaning Flue Ash







Circular Channel of Flue Gas



Baffle for Blocking Flue Gas


Metal Sheet


Outlet of Flue Gas





Brick (or Metal Sheet)

Woodstove and char coal stove construction and maintenance

· The dimensions of the pot (diameter and depth) must be measured correctly.

· The construction should follow the dimensions in the design.

· To prevent flue gas leakage's, seal brick layers with mortar.

· Insulate the bottom of the stove with ash mixed with salt and clay.

· The optimum chimney height is about 2.5m but this may need changing when the stove is first tested.

· Pay great attention to the distance between the pot bottom and the grate; for the normal pot (60cm), this should be 18cm for a firewood stove and 13cm for a charcoal stove

· In the firewood stove, the area of the grate can usually he taken as a quarter or a third of the area of the pot bottom Occasionally it will he as little as one fifth.

· The gap between the grate bars should be kept between 12mm and 14mm The bars will need replacing when burnt through.

· Plaster the external stove body with cement after two or three days.

· Ensure smoke passages do not become blocked.

Haiti: Cooking stoves and domestic energy

Editorial summary based on preliminary report by Peter Young of intermediate Technology Consultants and Betonus Pierre for CARE Haiti and the Haiti Bureau des Mines et de l'Energie; April 1996


Haiti is a pan of a large Caribbean island about 800 kilometers long, situated close to Cuba and to the Florida coast of the USA. It has a population of about six and a half million people, increasing by 5 per cent per annum in urban areas and by 0.7 per cent in rural areas. The country originally belonged to the French, it was occupied by the USA from 1915 to 1934 leading to a strong American influence in the country. Since 1994 Haiti has had a democratic form of government.

The climate of the island is humid tropical and the Haitan pan is largely mountainous. Agriculture is very poorly developed and holdings are generally too small to be farmed effectively.

Haiti is perhaps the poorest country in the Central American region with a GNP per head of 370 US$ (compared with Tanzania, which is reported to have a GNP per head of 100 US$). There are few natural resources; bauxite is the main one and there are unexploited deposits of low-grade brown coal. Only 3 per cent of its original forest cover remains, so much of the country is severely eroded.

Nearly a third of the population lives in urban areas and the urban population is increasing rapidly, especially in the capital, Port au Prince. The arable areas of the country have a very high population density of 800 per hectare. Nearly 60 per cent of the population is under 25 years old, literacy is 20 per cent, and school enrolment is only 52 per cent.

Figure 1 Comparative costs of charcoal in major charcoal consuming countries

Energy use

Households consume 92 per cent of all the energy used in Haiti. Nearly all of this (95 per cent) is either firewood or its derivatives. Charcoal accounts for 41 per cent of the fuelwood used, of which nearly three quarters is used in Port au Prince. The movement to urban areas has led to an increased demand for charcoal as the principal fuel.

The remaining household energy is provided by:

· kerosene 2 per cent
· electricity 2 per cent
· liquefied petroleum gas (LPG) 1 per cent

The minimum daily wage is US$2.23 (US$606 per annum). For those earning twice the daily minimum, 20 per cent of this will be spent on charcoal. The poorest 70 per cent of the population, mainly in rural areas, will generally collect fuelwood or other biomass rather than buy charcoal.

Table 1: Wood energy Consumption in Haiti 1990

Charcoal (x1000 Tonnes)

Firewood (X1000 Tonnes)

Wood Energy Distribution %


Informal Commerce & industry


Informal Commerce & industry


Informal Commerce & industry

Port au Prince







Other urban areas







Rural areas







Total per sector











Figure 2: Relative costs per megajoule of useful energy for different types of fuel

Fuel prices and trends

Despite the forestry resources of Haiti being severely depleted, the price of charcoal is considerably lower than in other major charcoal consuming countries (see Figure 1). This is probably due to the poverty-stricken rural economy which causes farmers to supplement their incomes by producing charcoal.

Fuel prices are very much affected by the quantity purchased. Poor households pay more than twice as much as rich households for cooking energy. This is probably due to an increasingly impoverished population who do not have enough cash to buy large amounts of charcoal at any one time. From Figure 2 it can be seen that:

· poor households could halve their current fuel expenditure if they could afford to buy charcoal by the bag, rather than buying enough to cook one meal.

· To cook the same quantity of food, the cost of using kerosene is about one third of that paid by the poorest households who buy charcoal in very small quantities.

Kerosene prices have remained very stable and look set to remain low compared to LPG because of the favourable price structure set by the government for imported fuels.

Economic benefits from switching fuels

From Figure 3, the following can be deduced:

· being able to switch to other forms of fuel energy could save the poorest households up to 8 per cent of their income per year

· for households rich enough to purchase bags of charcoal, butane would not provide savings.

Table 2: Summary of kitchen performance tests on improved charcoal stoves

Stove type households

Number of per household surveyed

% savings per capita

% savings

















Ret: Care & BME August 1995

Choice of appliances will depend on cost, convenience and comfort. The best option is probably charcoal for long slow cooking and kerosene or LPG for rapid cooking.

It has been estimated that 11 per cent of urban households own gas appliances. In energy terms, one tonne of LPG is the useful equivalent of 4.7 tonnes of charcoal. On this basis, 60 000 tonnes of LPG would be needed to replace the total Haitan demand for charcoal (a tenfold increase in current consumption).

Prospects for improved stoves

Charcoal Stoves

Fuel saving assessments using four types of stoves were carried out for low/middle income families with an average household size of seven persons per household. Table 2 shows the savings compared to a traditional charcoal stove. The Ceramic stove is a KCJ type; the Ronderosa (similar to a Burundi stove) originated as pan of the Rwanda World Bank project; the BME stove is one promoted by the Bureau des Mines et de L'Energie; three types of traditional charcoal stove were used (Entole, Potage, Masonry) and no significant differences in fuel consumption were observed so an overall figure is given.

To assess the impact of these stoves, the payback time before the stoves provided real saving were calculated. Table 3 shows the payback time for a ceramic stove and a traditional Entole stove.

LPG Stoves

During the period 1990-93, 80000 BiP stoves, known as 'Ti Cheri' stoves were sold. These are gas stoves which were sold at a very attractive price. The increase in gas stove ownership has not been matched by a comparable increase in gas consumption (and subsequent reduction in fuelwood use). The use of LPG represents, in energy terms, only about 11 per cent of the equivalent charcoal consumption. The popularization of the BiP stove has thus been disappointing in terms of the quantity of fuelwood saved. Gas has provided an additional energy source rather than a replacement and it will take favourable gas prices and improved availability before gas significantly replaces charcoal.

Table 3: Payback time for two improved charcoal stoves

Type of stove



Cost of stove (H$)



Savings H$/household/day



Payback time (days)



Annual savings (H$)




Gas prices are very competitive with charcoal, but the initial outlay for equipment and the recurring cost of a cylinder will remain a major barrier for low income and poor households because of their cash flow problems. However, gas usage will most likely grow at a steady rate, particularly amongst middle income households as they become more affluent.. Kerosene stoves are cheaper than gas stoves. In addition, kerosene can be purchased in small quantities depending upon a person's cash flow situation. In the short to medium term, kerosene stoves should be targeted at low income households whilst the gas companies should continue to popularise gas amongst the middle income households.

Figure 3: Percentage savings achieved by changing fuel supply or using an improved stove

Household energy in a recently electrified rural settlement in Mpumalanga, South Africa

Bernard T Luvhimbi and Harald H Jawurek, School of Mechanical Engineering, University of the Witwatersrand, Johannesburg, WITS, 2050 South Africa.

Wood is still the predominant source of energy for cooking and water heating, but much of it is now purchased, rather than gathered.

South Africa is in the process of rapid electrification. The number of houses newly connected to the grid was approximately 623,000 for the period 1991 to 1993, 436,000 for 1994 and 478,00() for 1995. It is estimated that this programme will increase household access to electricity for the country from 35 per cent in 1990 to 80 per cent in 2010. The households being electrified are mainly those of low income areas. These include - in descending order of income and present access to electricity - the traditionally black, formal townships attached to cities and towns, informal urban communities (shack settlements) and rural settlements.

The effect of electrification on household energy consumption has been studied for several urban and peri-urban communities in South Africa. Very little comparable post electrification information on rural, mainly wood-buning settlements appears to be available. This study looked at such a settlement.

During August and September 1994, an energy consumption survey in a traditionally wood-burning, recently electrified, remote settlement was carried out. The settlement that was studied was Green Valley (24°36'S, 31°01'E), adjacent to Acomhoek in Mpumalanga (previously Eastern Transvaal). Green Valley is an administrative unit of a low income, densely populated, urban like sprawl stretching for kilometers and set in a remote, semi-arid, rural region. Land area per household is of the order of 1000 m2; there is thus no question of subsistence agriculture, though gardening for food is practised, despite frequent water supply difficulties.

The electrification of Green Valley was started in 1990 and essentially completed in 1993. Very few houses were 'wired' in the conventional sense. The majority were fitted with a 'Ready Board', a simplified distribution board into which lights and appliances are plugged directly. The boards are operated by means of a magnetic card with which the customer repurchases electricity at a central pay-point in the settlement.

Data collection

Data was obtained mainly by means of structured interviews based on a questionnaire. A total of 80 randomly selected households was covered. Interviews were conducted in Pedi and Tsonga, the two local languages. Additionally, numerous informal interviews were held. The method involved determining how many households used each type of energy source. For a sample of this size, measurements to determine the exact quantities of each fuel consumed are problematic as they are both intrusive for the households involved and excessively time-consuming for researchers.


Figure 1 shows the percentage of households using various energy sources. All sample households in Green Valley use electricity and 84 per cent of households use wood. There is a sharp reduction in the use of paraffin when settlements are supplied with mains electricity. In the nearby non-electrified settlement of Cottondale paraffin is used for lighting (96 per cent of households), cooking (53 per cent) and refrigeration (7 per cent); in Green Valley it is used for cooking only - the paraffin lamp has passed completely out of use.

The use of dry cell batteries is considerably lower in Green Valley than in Cottondale. This is largely due to the reduced use of batteries in radios. The reduction would have been larger still had not many radios been of the battery-only type. In Green Valley (where all households use electric lighting) candles serve as backups in the case of power failures, or when the pre-paid card is out of credit. Coal, LPG and dung are not used by the Green Valley sample households; coal is not available and LPG is little known. Some dung possibly may have been used, but this was not admitted.

Table 1 shows the percentage of households which use grid electricity for specific functions The main Uses are: lighting, radio for news and entertainment, ironing, cooking and water heating (for washing and hot beverages). The percentage of households in possession of appliances for the last two activities is as follows: full electric stove (5 per cent); double electric hotplate (34 per cent); electric kettle (33 per cent).

Table 1 Percentage of Green Valley households using grid electricity for particular activities


Percentage of households





Radio/music system






Heating water (kettle)




Deep freezing


Cooling house (fan)


Heating house (heater)


Figure 1. Percentage of household using particular energy sources

Of the households using electricity for lighting only, 52 per cent stated that they had too little money to buy other appliances, 30 per cent that they had too little money to run other appliances, or that they had appliances (radios/music systems) but not the AC/DC adapters that permit operation off the mains. Only 8 per cent prefer the use of a non-electrical energy source - wood for cooking.

Of the 84 per cent of households using wood for cooking and water heating, 34 per cent use wood exclusively, 31 per cent use wood supplemented by paraffin, 10 per cent use wood and electricity, and 9 per cent use all three. Wood thus remains a major source of energy.

Table 2 shows how fuelwood is obtained. Purchased wood is obtained mainly from veld clearing operations for agriculture and from vegetation thinning in game reserves suffering from bush encroachment. All purchased wood was veld wood in this study; exotic plantation woods are, however, known to be used at times.

The transition from gathered to purchased wood has also been observed in non-electrified settlements in the area; it reflects the increasing scarcity of free fuelwood from the veld. Table 2 also shows a significant increase in the number of households that do not use wood at all. This is most likely due to the combined effects of wood scarcity and electrification.

Table 2 Sources of wood

Source of wood

Percentage of households

Green Valley 1994

Cottondale 1990

Gathered in veld






Free, collected by hired van



Households not Using wood




In a recently electrified rural settlement in Mpumalanga, electricity is extensively used for lighting and media applications, but less so for cooking and water heating. For the latter, energy intensive activities, wood remains the major fuel.

Comparisons can be made with results from earlier studies in urban and peri-urban areas where it was found that for cooking, water heating and space heating (high energy consumption activities), the 'old', pre-electrification fuels, predominantly coal (for settlements near the coal fields), paraffin (kerosene), and to a lesser degree LPG, remained in extensive use.

Rural households using wood for cooking were found (with a single exception) to use the traditional open fire built on the ground. There have been several attempts locally, and numerous programmes elsewhere, aimed at the development of low cost, wood-burning stoves that are more efficient and that pollute less than open fires. Woodstove programmes thus remain relevant in the face of rural electrification. With the increasing scarcity of traditional veld wood there is a major energy transition from gathered to purchased wood.

Improved Tunisian domestic bread ovens: Flying saucer lids save 50 per cent fuelwood

by Hanns Polak, (GTZ/Agence pour la Maitrise de l'Energie), BP 230, 7121, Barnoussa, El Kef, Tunisia

With its two and a half million inhabitants Tunis is today one of the big cities of the Mediterranean. It has been quickly growing over last decade, but despite that, Tunisia is a rather small country of barely nine million people.

Tunisians have maintained a taste for rural life. 'Bread' in Tunisia means mostly the French 'baguette' produced in large quantities in central bakeries in each town. It is cheap - less than 20 US cents for a pound - as its price is fixed by Government. For most people the Arabic word 'chobbs' is reserved for the 'real' bread which is still made in at least 500,000 tabouna ovens all over the country. It is flat and round; that cake shaped little something owes its aroma and taste and its golden brown crust to whole wheat flour and the fine scent of pine firewood. Baking requires five to six kilos of wood for each firing. Even though LPG has replaced the three stone fire for cooking, a tabouna still remains the heart piece of a Tunisian household, representing traditional values and continuity.

A women's technology

Baking bread in Tunisia is a woman's affair. In each village there is usually one lady who specialises in making the barrel shaped ceramic body of a tabouna oven. The procedure needs several days. After soaking the clay for two days the shaping is done by hand, without a potter's wheel. The barrel needs to dry for three to four days before it can be baked in the fire. The baking is done by covering the inside and outside of the oven core with a heap of dry twigs. These are burned reaching temperatures of between 500°C and 800°C which bake the clay.

After the barrel has been brought to the place outside the house where the tabouna oven will be finally installed, the housewife takes over. She insulates the outer surface with a mixture of straw and loamy soil, leaving two, three or four air holes at the bottom of the stove. In a few tabounas, which are constructed completely underground, there are no air holes at all. There is never a grate at the bottom of the tabouna; the ash is swept out through the holes or is extracted using a flat shovel. The mouth on top of the tabouna remains open to put the fuelwood and later on the bread into the oven. In the traditional way it is not covered while heating the oven.

If firewood is available, the housewife will start baking at once; usually, she will have to go and look for fuel. Groups of three or more ladies go together to collect firewood and shrubs. If the area is sparsely forested, they will leave in the early morning and return in the late afternoon, each carrying a load of about forty kilograms.

Although arduous, collecting fuel does allow women a chance to get away from the constant supervision of the menfolk in the family; this is the only time when womenfolk do get away from the family home. Fuelwood is an increasingly scarce commodity: there remains hardly anything burnable to gather, especially in the vicinity of villages and towns.

Many women use agricultural residues or they collect shrubs, such as rosemary, which are easily uprooted and may still be found after the forest wood has all been taken. However, this leads to erosion as the winter rains wash away the soil which had been held together by the shrubs and the next year the problem is even more severe

Tabouna lid

Even in already deforested areas 89 per cent of the households meet their energy requirements with approximately four tonnes of biomass per year. About 44 per cent of it is needed for making bread in the tabounas. At least one half of the tabouna-using households have to buy fuelwood in addition to what they collect.

Equipping the tabouna oven with a lid was the most promising solution to reduce the consumption of firewood. The lid is made out of sheet steel and is fixed by a hinge on to the tabouna. When the tabouna is in use, the lid is closed, thus retaining a large proportion of the energy that is normally lost with the traditional tabouna.


The project team sells more than 4000 lids per year and has developed a social marketing strategy to commercialise the lid. One of the field workers relates;

'In the beginning it was very difficult to convince the women... they were arguing that the taste of the bread would change when using a lid over the tabouna. And it was even more difficult to convince the men to pay the price of 9 dinars [about 9US$] for something which would in their view only serve their wives”

Over the two years work the team has developed a social marketing strategy to commercialise the lid.

The first thing we discovered was that the lid needed to be more attractive. The people wanted not only something that would save their time and money, they wanted something nice.

By using standardised moulds, imported sheet steel and a simple press, operated by a lorry jack, local blacksmiths can produce attractive lids that resemble mini flying saucers. The tabouna was converted into a real modem baking oven.

Marketing the lid

The lid was named 'Salha' a word that means in Arabic, 'useful' or 'good for'; a famous popular song carries the same title.

Demonstrating the usefulness to a target group of 150000 households was a more difficult job. As the field worker explained,

'...soon we realised that we were simply too small a group to go into each and every douar... without the help of other organisations and many other vulgaristrices [field workers] we felt we would need a hundred years to popularise the ".salha".'

Local agricultural advisers, NGOs, blacksmiths and sellers of household appliances were drawn into the scheme. They all needed to be motivated, trained and equipped with demonstration tools. Once the communication between customers, producers and regional agents was installed, radio and TV spots were produced and broadcast. Every possible event like environmental or agricultural fairs and seminars and local markets were used to advertise the lids.

Development from project to enterprise

'Before we discovered the mechanisms of the market the relationship between us and our target group was clearly defined: we were a rich project and they were the beneficiaries.'

This role led to a perception that the lids would be supplied free of charge. In order to supply lids to an increasing market it became essential to convert the project from a charitable project to a small enterprise.

'We do not say any more beneficiaries we talk about customers.'

Beneficiaries became customers; subsidies were ruled out; the lids are now sold at the commercial price. The enterprise makes a small profit as sheet steel and hinge material are free of tax and duty and the prices are fixed for a period of time. Although the project still depends on government finance, it works as an enterprise, depending on profits.

'We work like an enterprise our financial means are scarce so we have learned to employ existing partners.'

Politicians and administrators are used to promote the benefits as they are shown to be caring for the environment and their people. Controlling quality and price is necessary to avoid producers and customers being dissatisfied. External support will still be needed for a long time before all functions are taken over by private entrepreneurs.

Mumu: A traditional method of slow cooking in Papua New Guinea

P A Sopade, Food Technology Section, Department of Applied Sciences, University, of Technology, Lae, Papua Ned Guinea

One of the traditional techniques in Papua New Guinea is cooking with the mumu. The mumu is an earth oven that is formed by heating stones which are subsequently put in with the food or arranged around and on the food. The heat in the stones is transferred to the food to cook it. The earth oven is known by various names amongst the South Pacific islanders:

· in Samoa, Tonga and Cook Islands it is umu
· in Tahiti it is ahimaa
· in Solomon Islands it is motu
· in New Zealand it is hangi

Generally, black river stones are used and hard wood is preferred as fuel. All sons of food are cooked in the mumu at the same time, but usually the more delicate ones are put on top. The time spent cooking depends on the quantity of food being prepared; it can take anything from one hour to overnight. Mumu is often used during ceremonies, but even households with modem ovens will use mumu on occasions.

Types of Mumu

Papua New Guinea is a land of contrasts; from swampy plains to high alpine mountains and broad upland valleys. Mumu appears to be more common in the highlands, where pottery is very limited. The following types of mumu have been identified;

Rabaul mumu

Alotau mumu

1. Rabaul

In Rabaul a pit is usually dug in which the stones are heated. The size of the pit and the quantities of stones and firewood are dependent on the quantity of food to be 'mumurised'. While the stones are being heated, food is prepared with coconut cream and wrapped in banana leaves. The banana leaves are conditioned over the fire which is heating the stones. The charcoal is removed from the heated stones, and the wrapped food is placed on some of the hot stones. The remaining stones are place on top of the wrapped food before covering the mumu. With banana leaves and jute bags, neither sand nor earth is used and it is usually left for about four hours. All the foods are cooked together and the food is baked rather than steamed as the moisture in the mumu is limited to that held in the leaves and the food. The temperature of the food can be as high as 250°C.

A similar type of mumu was observed in the Western Province (Daru) but no pit was dug and tree bark was used in covering the mumu instead of banana leaves.

2. Alotau

This type of mumu is referred to as dry mumu because, even though the foods are wrapped and cooked together no coconut cream is used in the food preparation. A pit is dug and when the stones are hot. the charcoals are left amongst the stones. The food is wrapped as in the Rabaul mumu and it is put on the hot stones. More hot stones may be put on the food, but more leaves are used to cover the food before the dug earth is used to complete the covering and keep the heat within the mumu. Smoldering firewood is placed on the earth cover to keep the top layer hot.

The additional heat from the top ensures that a high temperature (greater than 200°C) is maintained in the mumu throughout the duration of cooking. The hot charcoals complement this. This relatively constant high temperature is needed to ensure that the food is properly cooked as the absence of coconut cream will reduce heat conduction. As with the Rabaul type. baking is the predominant process.

3. Goroka

This type is typical of mumu in the Eastern Highlands Province. The stones are heated in the pit and most of the charcoal is removed afterwards. Banana leaves are put on top of the stones and the food is wrapped in separate segments. Hot stones may be put in or on to the wrapped food and earth is used to complete the covering. Water is then poured on to the hot stones through a special opening. This generates steam within the mumu. More earth is used for the cover to keep the steam inside. The cooking duration in the Goraka mumu is the shortest, possibly because of the steaming effect. The food appears less baked than in the other forms of mumu and the temperature of the food is usually below 100°C.

Goraka mumu

Mount Hagen mumu

4. Mount Hagen

A different type of mumu is found in the Western Highland Province. A relatively deep pit is dug which is conical in shape. Stones are heated on the ground away from the pit, the bottom and sides of which are lined with banana leaves before some hot stones are put in. Food is transferred separately into the pit and the hot stones are put directly in the food. Coconut cream is not used and neither is water poured on to the hot stones nor are the food segments wrapped in banana leaves. When all the food has been put in, the protruding leaves from the sides of the pot are used in the final food wrapping. Grasses and additional banana leaves are used for the final covering to keep the heat within. Baking is expected to be the predominant form of cooking.

The temperature in the mumu can be as high as 250°C and because of contact between the stones and the food, the food approaches the temperature of the stones. The high food temperature demands that the mumu is uncovered within a short time to prevent over-cooking. It is unusual for this type of mumu to be left overnight. A similar type of mumu has been recorded in Western Samoa, but coconut cream was not used and no pit was dug.


Mumu is pan of the culture in Papua New Guinea and the field study revealed that mumu is cherished by the people. Mumurised foods are reportedly rich in flavour and are preferred to foods from conventional ovens for this reason. In theory, cooking foods in a mumu seems convenient, but in practice it is very labour intensive. Concerns have been raised concerning the fire hazard and environmental implications of the mumu materials. However, the major concerns must be the undercooking and overcooking of food and post cooking contamination, as well as migration of materials from stones to foods. At present laboratory tests are being used to examine temperature distribution in the types of mumu discussed above and associated microbiological issues.

Reducing the risks of poisonous emissions from stoves

Grant Ballard - Tremeer and Harald H Jawurek, University of Witwatersrand, Johannesburg, South Africa.

To keep warm in cold climates, fires and stoves are needed for space heating as well as for cooking. These fires are often in rooms with little ventilation and they bum for long periods. People are thus exposed to high levels of combustion emissions for a long time - the health impact of these emissions on the users is therefore particularly severe.

The health effects from combustion emissions range from headaches and breathing difficulties to death. These effects may be immediate or occur after being exposed to the pollutants for a long time. Some symptoms may show up only many years after exposure. The effects depend upon the type and quantity of the pollutants, the duration of exposure to them, and on the age and health of the person exposed. There is increasing evidence that chronic exposure to carbon monoxide (CO) constitutes a long-term health risk.

At the University of the Wilwatersrand in Johannesburg, South Africa, the CO and smoke emission patterns have been recorded for a number of cooking devices including the traditional 'three stone' fire, as well as a number of improved stoves. It was found that enclosed stoves all have greater stove efficiencies than the open fire but also had greater emission levels.

In an attempt to improve efficiency, thermal contact between the fire and the base of the pot has been increased in improved stoves by enclosing the fire, but this results in the combustion gases being less completely burnt. In addition, in an enclosed fire, the flames are 'forced' on to the base of the much cooler pot, thus quenching them and causing 'freezing' of the volatiles and their emission in partially burnt states.

Emission rates were recorded for CO and smoke every ten seconds throughout a bum cycle; this involved heating water to boiling point rapidly and then simmering for 30 minutes. Figure 1 shows room concentration of CO for a one-pot metal stove with ceramic insulation which is top fed. Notice the high room concentrations reached for the metal stove. The line shown at 0.1g/m3 (equivalent to 87ppm) is the level of the 15 minute World Health Organisation air quality guideline for Europe. Notice that both the three-stone fire and the metal stove exceed this level for most of the bum cycle. After 40 minutes, room concentrations for the metal stove are twice as high as for the open fire. From the above discussion we offer the following recommendations:

Figure 1: CO concentration in a room with poor ventilation

· For space heating, improved stoves must have chimneys so that combustion gases are removed from the dwelling. The Indian Chulha with a chimney, although its efficiency is low (as can be expected for large mass mud stoves) is a good example. Mud stoves without chimneys are not recommended.

· Do not assume that improved stoves without chimneys are safer than the traditional open fires. Enclosed stoves in general emit higher levels of poisonous gasses than three-stone fires. Stoves which are 'fed' through the same opening as that which supplies air for combustion have the danger of being over-stoked (in an attempt to prolong burning). The more fuel in the combustion chamber, the less space there is for air, and emissions will therefore increase significantly. Stoves providing combustion air principally from beneath the fire through a metal or ceramic grate can clog with ash and gradually cause the fire to smother; again greatly increasing emissions.

· Particularly large quantities of poisonous fumes are emitted during stove lighting and refueling because cold pot sides and stove sides cool the flames and result in less complete combustion. Because of this, portable stoves without chimneys should be lit and operated out of doors for at least ten minutes before being brought indoors. This practice is frequently followed in South African informal settlements with coal-burning braziers, 'Mbaulas', made from 25 litre drums. Refuelling indoors is dangerous (although peak emissions after refuelling are usually lower than after initial ignition owing to reduced quenching on the sides of the stove). No fire (even a glowing one) should, however, be operated in a room with poor ventilation.

· Overall efficiency can easily be improved without reducing combustion efficiency by raising the fire off the ground by means of a grate. This improved three stone fire has an efficiency comparable with enclosed stoves (21 per cent) but with much lower emissions.

Update on biogas in Nepal

Summary from Biogas and natural resources management (BNRM) Nepal'

With the rapid depletion of forest resources in Nepal, alternative sources of energy must be sought. Biogas is one of these sources, which not only saves firewood but also has the potential to increase soil fertility, improve sanitation and reduce the workload of women.

In November 1992, an agreement entitled the 'Biogas Support Programme (BSP)' was signed between His Majesty's Government of Nepal and the Netherlands Development Organization. The long term objectives of the BSP are:

· to reduce the rate of deforestation and environmental deterioration by providing biogas as a substitute for fuelwood and dung cakes in order to meet the energy demands of the rural population;

· to improve health and sanitation of the rural population, especially women. This was to be achieved: by elimination of smoke produced during cooking on firewood; by reduction of the hardship involved in the collection of firewood; and by stimulation of better methods for dealing with dung and night-soil;

· to increase agricultural production by promoting an optimal use of digested dung as organic fertilizer..

The programme was divided into two phases. The short-term objectives, to be reached by July 1994, were:

· to construct 7000 biogas plants;
· to make biogas more attractive to small farmers, and farmers in the hills;
· to formulate recommendations on the privatization of the biogas sector in Nepal.

The second phase, started in July 1994, has the following aims:

· to install 13 000 quality biogas plants using both the implementing agency and private construction companies;
· to support the establishment of an apex body to co-ordinate the different actors in the biogas sector.

Dung is the main potential source of biogas. The production of biogas is limited by altitude and access to water. The number of households with cattle and or buffalo in Nepal in 1992 was calculated as about two million. Installation of biogas is technically possible for 65 per cent of these households (about 1.3 million), with average digester size estimated as about seven cubic metres.

The project to date

Six different sizes of digester have been installed ranging from four to twenty cubic metres total capacity (digester plus dome).

These plants work well for households with cattle but have not proved successful for community biogas plants, mainly because of social factors.

By providing a subsidy whose value was the same for all sizes of plant, small farmers with few cattle were encouraged to take part in the scheme. A larger subsidy was given for those living in the hill districts as the transportation costs of moving the digester on to their farms was perceived to be greater.

At present, twenty-three biogas companies construct and install biogas plants and eight more have been approved to construct them. Recently, the Nepal Biogas Promotion Group has been established. Promotion, training and extension will be taken up by this group in the near future. NGOs have entered into agreements with biogas companies to promote biogas in their regions. Two banks have recently decided to invest in the scheme, and this has helped to finance the programme.

Strong emphasis has been given to the quality of construction, maintenance and operation of the biogas plants.

Impacts and benefits

Several studies have shown indoor air pollution and smoke exposure in rural Nepal, expressed in respirable suspended particulates (RSP), carbon monoxide (CO) and formaldehyde (HCHO) to be among the worst in the world. Smoke is one of the major risk factors for acute respiratory infections in infants and children and is a major cause of child mortality in Nepal. The installation of biogas plants has resulted in significant health benefits. The main positive effect is on the level of indoor air pollution. Eye ailments, commonly associated with smoke-filled rooms have been reduced by the reduction in smoke.

It has been estimated that just over three hours a day can be saved by an average household by installing biogas.

Women who use biogas express great satisfaction with it. They are able to do other activities as the cooker does not require constant attention. In summer, the heat produced is less; however, in winter they miss the extra warmth.

Biogas can only be used by farmers who own cattle. The poorest in society therefore do not benefit directly. Nevertheless, by promoting biogas use, pressure on the more traditional fuelwood sources is reduced and if fuelwood is more plentiful, the poorest people may be indirect beneficiaries.

Research and development

Research into integrating a wood/charcoal stove into building design

N K Bansal and M S Bhandari, Centre of Energy Studies, IIT, Hauz Khas, New Delhi - 110016, India


An idea for integrating a cooking stove in the kitchen into the design of a building has been investigated for space heating in cold climatic conditions. The exhaust gases from the cooking stove are made to flow through a cavity wall, which acts like a chimney. The wall stores the heat during cooking hours and keeps the inside space at a comfortable temperature provided the heat loss rate from the building does not exceed 0.5 W/m2degK.


In many regions of Nepal and India there is a need for heating round the year. This is usually achieved by using a wood stove which is also used for cooking. The usual three stone fires, have now been replaced by cleaner, more efficient cooking stoves. Although stoves of this type are designed with a chimney, most of them are not integrated into the building design. In this paper, we examine the possibility of integrating an efficient wood stove into a building, which may provide both cooking energy and the energy for space heating.

Stove design

Table 1 gives the amount of fuel needed to cook 1 kg of various foods. It is seen from the table that, theoretically, 18gm of wood per kilogramme of food cooked is required for cooking, but in practice approximately 268gm of wood is used up in the fire. Some stoves have been considered in detail to determine the quantity of energy lost during the process of combustion and cooking.

Stove efficiency

For improving the overall efficiency (PHU) of a stove, a number of factors should be considered:

Combustion efficiency: the maximum amount of energy which can be converted into heat as a percentage of the calorific value of the fuel.

Heat transfer efficiency: the maximum amount of energy which is transferred to the pot. This includes conductive, convective and radiative heat transfer processes.

Control efficiency: the mechanism which allows only as much heat to be generated as is needed to cook the food.

Pot efficiency: the characteristics of the pot which affect the proportion of heat reaching the food through the pot.

Cooking process efficiency: how efficiently the heat which reaches the food converts the raw food into cooked food. Combustion and heat transfer efficiencies are often combined for convenience and these are termed the thermal efficiency of the stove. When these are combined with the control efficiency and the pot efficiency, the efficiencies combined together are called stove efficiency.

Heat transfer processes

Heat conduction: when cooking begins, the walls of the stove are cold. With time, they warm up at a rate which is dependent on both the weight of the walls and their specific heat. Lightweight walls warm up quicker than heavier walls.

Heat transfer to the pot by convection: when a pot is being heated by hot gases leaving the fire, the factors which affect the amount of heat reaching the pot by convection are:

· the area of the pot which is in contact with the hot gases;
· the difference between the gas temperature and the temperature of the pot.

To increase heat transfer to the pot by convection three things can be done:

· the temperature of the hot gas can be increased by the choice of stove and by controlling the amount of air that enters the stove;

· increasing the area of the pot exposed to the hot gas. The pot support should be small and strong, occupying a small area and allowing the hot gas flame to rise up around the pot and contact the surface;

· the maximum heat transfer coefficient should be increased. This can be done by increasing the velocity of the hot gas.

Heat transfer to the pot by radiation: the radiative heat transfer to a pot depends on the temperature of the tire bed, the areas of the pot and the fire bed, and the distance between the two. To heat the pot more effectively by radiation the alternatives are:

· increasing the fuel bed temperature and thereby increasing the heat radiation from it;
· lowering the pot and thus reducing the distance between the pot and the fire bed;
· increasing the area of the pot 'seen' by the tire bed.

Figure 1: Hypocaust system integrated in a building

Figure 1: Hypocaust system integrated in a building

Combustion efficiency

Combustion of biomass is an extremely complex process involving chemical kinetics, heat processes, molecular diffusion and other phenomena. The most important parameters in wood combustion are the moisture content of the wood and its calorific value. Usually the calorific value per kilogram of any type of wood does not vary by any significant amount from any other, though the densities can be very different. The density does not affect the stove efficiency. Moisture content affects both the calorific value and the rate of burning very significantly.

Wood is typically composed of 80 per cent volatile material and 20 per cent fixed carbon and it is these percentages which determine the calorific value. In wood combustion, when the temperature reaches 100°C, the water is boiled out. From about 200°C, the hemicellulose begins to decompose, followed by cellulose decomposition. At about 300°C, decomposition becomes extensive when only 8- 15 per cent of cellulose and hemicellulose remains as fixed carbon and the rest is released as volatile gases. As volatiles escape the wood, they mix with oxygen in the air at about 550°C and ignite to produce a yellow flame. The flame not only radiates energy to the pot but it also maintains the combustion process. Burning of volatiles accounts for two thirds of the energy released by fire and the burning charcoal left behind accounts for the remaining third. A variety of techniques are used to increase the combustion efficiencies:

· use of grates which allow better mixing of air with fuel bed
· preheating of incoming air
· optimizing the shape of the combustion chamber
· insulating the combustion chamber

Heat of exhaust gases and building design

The escaping hot gases from a wood charcoal stove arc at a high temperature, between 300°C and 500°C These flue gases can be made to flow through a hollow wall in a 'hypocaust system', as shown in Figure 1 which is a conceptual drawing of a cooking stove integrated into the building design.

In the hollow wall, a cavity 50mm deep is created. A room of 10m2 floor area and a height of 3m, adjacent to the kitchen, has been considered. A daily variation of room temperature has been simulated and compared to the corresponding outside temperature at the same time of day. The performance of the experimental stove has been studied keeping all these parameters in mind.

To ensure good combustion the amount of air supplied for each kilogram of wood burnt should be at least 7m3. For most stoves used in developing countries, 1 kg of wood is burnt in about an hour, which corresponds to a power output of 5.5kW.

Results and Discussions

The following conclusions have been drawn from this study.

· the largest heat losses occur (1+ 42 per cent) through heat conduction into the walls of the stove

· the loss of energy into hot flue gases accounts for 22-39 per cent of the total input to wood stove

· incomplete combustion amounts to about 8 per cent

· typically half the energy entering the pot is lost in the form of steam. This is the energy lost at the point of use and mainly depends on the design of the pot.

The results of the hypocaust wall show that to provide adequate heating, it is sufficient to use the stove for 2 hours in the morning and 2 hours in the evening. The most important pan is to keep the building's envelope U-value at 0.5 W/m m20K which corresponds to a 5cm thick layer of insulation or an 80 cm thick mud wall

Table 1: Energy and theoretical amount of wood required for cooking food


Sp. Heat KJ/Kg °C

Temperature change °C

Energy required for chemical reaction kJ/

Food cooking energy kJ/kg

Wood equivalent gm./kg of cooked food




















2.01 -3.89

















* Includes sufficient water for cooking but none for evaporation
** For wood with a calorific value of 18 MJ/ kg