Biomass resources for energy: The critical issues

From the discovery of fire until fossil fuels made possible and indeed accelerated the industrialization process, biomass was, besides muscle, society's main source of energy. It is still the only source to which many people have access. Until recently, biomass based energy was derived almost entirely from combustion of fuelwood, crop and livestock residues. Biomass is actually by far the largest renewable energy source being used, with fuelwood alone accounting for more than one-fifth of total energy consumption in developing nations.

The possibilities of producing commercial energy from biomass, however, have risen mainly as a result of the fossil fuel crisis of recent years. As an energy source, the plant and animal materials that comprise biomass offer important advantages: they are renewable, they provide a relatively cheap and adaptable way of storing solar energy, and they are generally available locally. In a world in transition from the present international economy based primarily on hydrocarbons to one based increasingly on new and renewable sources of energy, the importance of biomass is undeniable.

Interrelated problems

Biomass resources potentially useful for energy are substantial but not always readily available. There are numerous interrelated physical, geographical, economic, social and environmental problems. The possible competition with other uses should not be underestimated. For this reason options for mobilizing biomass resources for energy should be assessed within the context of the broader rural systems within which they exist. The economic and social factors are as important as the physical ones, as the ultimate aim of any option is the welfare and development of man. Following is an overview of the magnitude of the biomass resource, a review of the main production options and a discussion of some important aspects to be taken into account in considering biomass energy resources in the context of integrated energy systems.

The potential magnitude of biomass resources for energy in venous ecosystems is shown in Table 2. The total energy content of annual terrestrial biomass production is equivalent to 40.6 billion tons of oil, or to approximately seven times the 1978 world commercial energy consumption. The stored terrestrial biomass has a total energy content of approximately 640 billion tons of oil, which is equivalent to the proven fossil fuel reserves.

Thus both annual production and stored resources are substantial, but this potential should be looked at cautiously. Most of the annual production occurs on land growing trees and shrubs (68.5 percent) and on savannah and grassland (16.2 percent), with only 7.8 percent of biomass production coming from cultivated land. Forest and shrubland are even more dominant as a source of stored biomass accounting for over 92 percent, with four percent on savanna and grassland and less than one percent on cultivated land. Thus, based upon global biomass production and stored biomass resources, energy that could be derived from such cellulosic material as trees, shrubs and grasses would seem to have the greatest potential, but how much of this material would be actually suitable for energy production remains to be clarified. The limitation of using agricultural crops is further evident when one considers that converting the entire 1978 world production of cereals, root crops and sugar to ethanol would have met less than 83 percent of the world's 1978 automobile gasoline fuel needs and only six percent of the world's total commercial energy needs.

Quantity not known

Even for the biomass accumulated in forest and shrubland, these estimates provide only an approximate order of magnitude: they do not include the regrowth of forest vegetation on lands where forests have been destroyed and which are abandoned after a short period. On the other hand, they also include large areas of very low biomass productivity due to severe ecological conditions and areas that are physically and economically not accessible. Therefore the area or quantity of biomass resources available and suitable for energy purposes is actually not known.

The appraisal of the biomass resource available for energy presents numerous methodological as well as other problems. The quantitative assessment cannot be separated from a qualitative evaluation. To take only the example of forest biomass assessment, there are a number of conceptual as well as methodological adaptations that are necessary as compared with conventional inventories. 3 Quantitative appraisals are complicated because arborescent vegetation exists in many forms, and there should be a clear indication of the elements of the plant that contribute a suitable material for energy production. It is therefore indispensable that the real potential of biomass resources for energy be assessed in terms of the amount that is practically available in quantities and qualities related to the energy needs or end uses. Otherwise, a broad evaluation would be of little use to the planner and decision maker, especially if the economic parameters are not adequately considered.

The conditions under which biomass resources are normally available will limit seriously their potential use for energy: one basic question is how to improve the productivity of biomass for energy in such a way that its potential can be further mobilized on physical and economic conditions suitable to the end uses. The three main options are: mobilizing more of the available resources, increasing the productivity of existing resources, and energy crops.

Substantial additional amounts of biomass can be mobilized for energy either by recovering large volumes of residues from forestry or agriculture or by bringing into production extended areas of marginal lands. Large volumes of woody vegetation or of agricultural residues are left in the soil after selective cutting of forests and after logging, after land clearing for agriculture or after harvesting agricultural crops. Relatively large areas of marginal lands are left unmanaged because of their marginal economic productivity, but their natural vegetation can now be used economically for energy. In both cases, the higher prices for energy products since the fossil fuel crisis have improved the economic conditions for the increased mobilization of available biomass resources; this has been accentuated by the recent developments in harvesting technologies and equipment. If this further mobilization is combined with other production functions in a joint operation, the economics can improve substantially.

Large areas of forests and other woodlands are poorly managed or not managed at all. Their productivity is markedly affected by such natural and human causes as climatic variations, fires, overgrazing and misuse of land by man. Substantial additional supplies of biomass for energy, particularly of fuelwood in the developing countries, could result from increasing the productivity not only of forests but also of scattered woody vegetation, open woodlands and small woodlots at farm or village levels. Although basic knowledge usually exists, in many cases adapted treatments need to be further developed. Involving the rural population is essential and to be successful the relative economic advantage in combining energy production with other agricultural or silvicultural outputs should be clearly demonstrated. Here again, the combination of energy production with other outputs will probably result in the best economic returns. Even in managed forests, management plans can usually be adapted to integrate energy production without notably reducing the other outputs.

Table 1 Fuelwood 1 in world and energy consumption, 1978

Source: FAO
¹ Including wood for charcoal.
² The total of fuelwood plus commercial energy excludes other sources of noncommercial energy important in some areas.

Energy cropping

Energy cropping is the third option that recently attracted growing interest as a way to increase energy self-sufficiency, particularly in liquid fuels for vehicles and feedstock for certain industrial processes. Energy cropping usually means growing plants for energy purposes: this includes trees, sugar and starch, vegetable oil crops, grasses and aquatic plants. Considerable work has been done recently on fast-growing trees with important successes such as the famous Ipil-Ipil. Much more can still be achieved by utilizing the potential of genetic improvement and species selection, particularly in application to local species. Still more can be achieved by applying intensive cultivation and management techniques and by finding suitable ways of combining tree growing with agricultural crops. This is probably where the largest long-term potential lies for increasing fuelwood supplies in the Third World. But once the processes of converting lignocellulosic material into liquid fuels and feedstock has become fully economic, energy cropping will also be quite promising for the developed countries and could become an important dimension in forestry.

Where sufficient suitable land is available, sugar and starch crops can be grown for ethanol production: this covers maize, wheat, cassava, sugarcane and sugar beets and sweet sorghum. Sugarcane has the highest yield of ethanol per ha of all energy crops. Sweet sorghum would appear to come next, but the performance under various soil and climatic conditions is not well established. Maize is the highest yielding cereal. Cassava grows under different climates and in a great variety of soils even of lower quality: it is probably possible to increase significantly the currency low average cassava yields per ha and thus the ethanol production per ha. However, as most of these crops are also food crops, developments of energy production programmes have to be carefully monitored in order to ensure their compatibility with national food policies and to avoid disruptive effects on food supplies.

Vegetable oils include sunflowers, soybeans, rape and oil palms, which produce oil for engines. The technology for processing the oil is quite simple, but the substantially higher value of the oil as food limits its development as an energy crop to relatively isolated locations where fossil fuels are difficult to obtain. A number of plants, such as the rubber tree and certain species of Euphorbia, produce hydrocarbons. Euphorbia is particularly interesting as it grows in semiarid locations.

Plantation programmes

Under current developments, increasingly large fast-growing tree plantation programmes are being developed in many countries, but many uncertainties still apply to other large energy cropping programmes. This is not only due to their possible impact on food supplies and prices; it is also related to the social and environmental effects as well as to the fact that major programmes required substantial subsidies for their establishment and implementation.

It is important that the options for biomass production for energy be carefully considered in relation to the specific rural system in which they will have to be integrated. Important issues relate to the characteristics and limitations of biomass-based fuel and its suitability to meet energy needs (i) for domestic purposes, (ii) for increasing the productivity of agriculture and rural industries and (iii) for complementing or replacing fossil fuels.

The fuelwood crisis deserves particular mention because of its impact on daily household needs and of its widespread repercussions on the predominant economic activity of crop and livestock production. The deforestation accompanying excessive fuelwood cutting is leading to such environmental consequences as degradation and loss of fertile soil, increased flood damage and downstream sedimentation of dams. Scarcities of fuelwood cause crop and livestock residues to be diverted to fuel uses, thus reducing their availability as fertilizer and (in the case of crop residues) livestock feed. The need to use more human labour to procure household supplies of fuelwood diminishes its availability for agricultural work. This clearly indicates that the fuelwood crisis is not just an energy issue and that a better integration of forestry and agricultural practices, for example through intercropping with leguminous woody species and agroforestry, will do more than supply an important part of rural energy needs. Planting fast-growing multipurpose trees helps solve the fuelwood problem, improves the welfare of rural communities, particularly the poorer groups, and contributes to maintaining a productive environment.

There are also a number of technologies that on the basis of renewable sources can produce more elaborated forms of energy; they are particularly well suited to the requirements of rural areas because they tend to be most readily exploited on a small scale and decentralized basis. Gasification is one example. They are potential sources of mechanical or electrical power that can either improve the quantities and qualities of energy to raise the productivity of traditional agriculture and of rural and forest industries or make it possible to provide modern services like lighting, pumping for irrigation and water supply, and refrigeration to rural communities and farms.

In selecting biomass energy production options and in integrating them into rural energy systems some basic questions need to be clarified, particularly with regard to the site specificity of each case:

- the development potential of the option in relation to the ecological conditions, the land availability and the agricultural situation;

- the nature and magnitude of present and future energy needs and the comparative advantage of this option to meet these needs;

- the costs and benefits involved in the option, taking into consideration the full range of economic, social and environmental effects; the level of investment required and the extent to which local resources can be mobilized;

- the maturity of production, conversion and end-use technologies for implementation, their relationships with existing knowledge and skills and their acceptability and impact within the social system;

- the infrastructure and institutional changes that may be necessary to provide political and technical support and guidance.

Table 2. Terrestrial biomass resources

1 Assuming 15 X 10⁹ joulesIton of dry matter
Source: H. Lieth and R.H. Whittaker, Primary Productivity of the Biosphere (Springer, Berlin, 1975)

Not technocratic

The approach should not be technocratic but should recognize the importance of the human dimension. Biomass resources production and mobilization for energy take place in rural areas, so they should be adapted to the orientations and objectives of rural development.

The above analysis shows the extremely wide ramifications of the potential of biomass resources for energy. The main issues are related to mobilizing action to utilize more fully the potential of biomass resources for energy. This is a complex undertaking, but three important questions need to be faced.

First, the potential of biomass resources for energy should be fully integrated in both national energy and rural development policies and programmes: they should recognize the potential as well as the limitations of biomass energy production. The most uncertain and controversial national policy area concerns the use of agricultural crops produced specifically for the purpose of providing commercial energy to replace fossil fuels. In the longer term, the production of liquid or gaseous fuels from wood and from crop residues that would not compete with food crops could become an important source of such fuels. Energy crops based on food crops could prove to be no more than a temporary solution. In the meantime, policies encouraging energy cropping should be pursued with caution and flexibility, bearing in mind their possible repercussions on food supplies, their necessary integration in land use and agricultural development planning and their social as well as environmental implications. At the same time, a fuller mobilization of the biomass potential in lands not used for agriculture, such as forests and shrublands, should be pursued: the advantage is that generally this can be done without competing with agriculture or with the other productive and protective functions of these lands.

Second, substantial efforts are still required in research and development and in training for biomass energy programmes. Research on biomass energy production is still new, and large biomass programmes require a solid basis of proven technologies, appropriate plant selection and suitable management methods. Because the location specificity is determinant to the success of such programmes, the transfer of knowledge is necessary but not sufficient: research and development capacities should be developed locally. The human resource is a key factor: biomass production programmes require new professionals and new skills. New capabilities are needed both in the technical and in the social area. The new techniques of intensive cultivation of fast-growing plants do not coincide with the traditional skills of the forestry and agriculture professions. The social dimension requires careful preparation in order to ensure that the biomass production programmes be really development-oriented. The challenge lies in the quality of research and development efforts, which should provide the basis on which to build the success of future biomass programmes.

International action

Third, probably the most immediate critical national and international issue is the continuing dependence of nearly two billion people on biomass energy in the developing world and the worsening fuelwood crisis. Solutions can only be national and local, but international action plays a critical role, being primarily educational, stimulating awareness of the importance of fuelwood in rural energy and assisting countries to develop the capability to formulate and implement adequate action. In many cases massive action programmes are urgently required to address fuelwood shortages and their social and environmental consequences. An important issue is the extent to which the international community is prepared to contribute the assistance required to support national efforts. Another international issue lies in the emergency situation that some countries may face in their rural areas when minimum energy needs can no longer be met by disappearing fuelwood. The environmental consequences of fuelwood scarcities and their indirect effects on food production (including that in neighbouring countries) are also important issues for international consideration.

In conclusion, biomass resources for energy are large, but they are not easy to mobilize: their variety and scattered nature, the diversity of ecological conditions and the possible competition with other uses are limiting factors. No general indication can be drawn on the most appropriate ways of mobilizing the important potential of biomass production for energy: however, current research seems to indicate that some important breakthroughs are possible that could meet from within the rural sector a substantial part of the increased energy needs required for rural development and at the same time make an important contribution to national energy balances. Special consideration needs to be given to the major role that traditional biomass never ceased to play in the supply of fuelwood in the developing countries. But an advantage of biomass is that it can provide the ground for a "soft" transition from traditional to modem technologies without brutal disruption of the way of life and organization of rural people - for example, from fuelwood to electricity generated through gasification of the same biomass material. Therefore all the attention should be on mobilizing action and developing biomass production systems for energy that are environmentally, socially and economically sound and that contribute to the energy needs of the people not only for their subsistence but also for their development. The importance of biomass in relation to national energy balances particularly in developing countries is strategical not only in quantitative terms but also in meeting the needs of large but scattered and often relatively isolated populations to whom the cost of distribution of commercial fuels could easily be prohibitive.