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close this book Diffusion of Biomass Energy Technologies in Developing Countries
View the document Acknowledgements
View the document PREFACE
View the document OVERVIEW
View the document 2 ENERGY AND DEVELOPMENT
View the document 3 NEEDS OF THE POOR
View the document 5 TECHNICAL FACTORS
View the document BIBLIOGRAPHY
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Biogas, alcohol, and thermal gasification technologies can provide the energy to farmers for machinery used in producing and processing agricultural commodities; to local entrepreneurs for energy to power small-scale industries; and to households and local communities for cooking, heating, and lighting.

These technologies are dependent on the production and efficient use of biomass. In view of the importance of increasing the availability and ensuring the renewal of sources of biomass for energy purposes, biomass generation is treated in this report as a separate technology with distinctive diffusion characteristics.

Other renewable energy technologies have been excluded from consideration here because of the greater relevance of biomass energy technology to increasing agricultural productivity and the more immediate dependence of the poor in the developing world on biomass as an energy source. It is assumed that whatever is learned about the diffusion of biomass-based renewable energy technologies may also be applicable to dissemination of other renewable energy technologies.


Biomass, which is organic material usually of plant origin, is generated as a feedstock for transformation into usable energy, either deliberately and wholly for energy purposes or as a by-product of forestry or agricultural production. It includes the following types of material:

Fuelwood -- Wood grown wholly or mainly for energy purposes, in plantations or as a component of agroforestry or social forestry systems. Firewood is any wood used in cooking or heating fires; fuelwood is wood transformed into other types of fuel, such as methanol or charcoal.

Residues or by-products -- The material remaining after the removal of the forest or agricultural product (the timber or crop). Sawdust, logging residues, crop stalks, and milling husks are included in this category, as well as animal wastes.

Crops -- Biomass grown specifically or partially for energy purposes; sugarcane, cassava, beets, sweet potatoes, and other starchy crops that can be converted into glucose for fermentation to alcohol; soybeans, sunflowers, oil palm, etc., that can provide vegetable oil substitutes for diesel fuel.

Agroforestry, Social Forestry, and Fuelwood Lots

Agroforestry provides a diversified output of forest and agricultural products by combining agricultural crops with trees and livestock on the same unit of land. It is designed to achieve more efficient use of sunlight, moisture, and nutrients than is possible through monoculture and to maintain or improve soil quality.

Trees are often intensively cultivated in homestead areas and may be grown elsewhere on agricultural land as windbreaks, boundary markers, for erosion control, or to provide shade or green mulch. Trees may also be grown as cash crops.

Social or village forestry involves tree planting on marginal lands or areas bordering agricultural plots, roadways, homes, or canals. Fuelwood lots are usually established on larger protected plots set aside for this use by communities or governments, and employ forestry rather than agricultural techniques.

While agroforestry is an ancient practice, it is not yet a science. Research is still needed to determine which trees can be most successfully grown with which crops, which fast-growing trees are best combined with slower-growing species, which varieties can best withstand particular climatic conditions, and which can best meet the needs of local populations. Because of the multiplicity of technical and social variables entailed in agroforestry, it is, perhaps, the most complex of the biomass-based technologies under consideration. But with its immediate relevance to the issue of biomass generation, improved quality of life, and conservation, it is also the most critical and the most promising.


Biomass is converted to useful energy through cooking stoves, charcoal kilns, gasifiers, and biogas and alcohol units.

Cooking Stoves

In many developing countries, the greatest proportion of national energy is consumed in the form of firewood or charcoal for cooking (and to a lesser extent, heating and lighting) purposes. The efficiency with which firewood and charcoal is traditionally burned is very low-perhaps 5-10 percent of the potential energy is actually transferred to the material being heated, Consequently, much effort has been directed to designing and diffusing stoves of higher efficiency, thereby reducing the amount of fuel required.

The three factors that most affect fuel use are moisture content, completeness of the combustion, and the efficiency of heat transfer. Air-dried wood yields approximately twice as much heat (on a weight basis) as freshly cut wood. Incomplete combustion, poor heat transfer, and heat wasted during heating and cooling are the principal causes of the energy inefficiency associated with open fires and the simple stoves used by the poor in most developing countries. Among some of these peoples, the smoke from open fires is recognized as an eye irritant and as the cause of respiratory ailments. Among others it is appreciated as a means of driving away insects. Among nearly all families dependent on fuelwood, time spent in the increasingly long search for fuelwood is a growing burden, especially for women and children.

Improved woodstove design requires a way to provide more efficient heat transfer to the cooking pots by enclosing the fire and regulating the air flow, Estimates of efficiency and potential energy savings are impressive, but usually unsubstantiated in the field.

De Lepeleire et al. (1981) have issued a compendium of stove designs. Over 100 models are described--many traditional and some experimental. From simple, shielded variations of three-stone fires to complex multicavity, multicontrol, monolithic units, these stoves represent a broad spectrum of candidates for improving fuel efficiency. However, the problem is to make new stoves acceptable by adapting them to meet the widely varying circumstances and cultural expectations of diverse populations. For as Ashworth and Neuendorffer have observed: "Cooking is one of the most culture-bound human activities. Food preparation, serving time and place, food flavor, and cooking participants often are established by long tradition and, therefore, are resistant to change. Social and religious customs may dictate all of the characteristics of the energy demand and may eliminate certain technology options even if energy output is . . . good. . . " (Ashworth and Neuendorffer, 1980).

Yet it is equally true that all over the world cooks have quickly and happily adopted gas, electric, or kerosene stoves, even at considerable expense. Historically, there are many examples of significant changes in diet taking place over short periods--most of the food produced in modern Africa is from nonindigenous crops or animals, and the taste for wheat-flour bread is ubiquitous. This underscores that the difficulty in diffusing "improved" stoves may be due to the lack of perceived improvement, either in convenience or efficiency.


Because it has a higher heat content and burns with a hotter flame, charcoal is more energy-efficient than fuelwood (though much of the energy content of the wood is lost in the conversion process). It emits more uniform heat and relatively little smoke, weighs less, is more readily transported, and is easier to store. For these reasons it is preferred to fuelwood by most urban dwellers. Its production and sale can be a valuable source of income.

Charcoal is also capable of meeting needs that cannot be met with fuelwood, such as use as a reductant in the iron and steel industry. And certain types of charcoal products (briquettes, for example) enable the use of shavings, sawdust, and other residues from forest products. Organized charcoal production also allows the use of larger residues (such as branches) from the logging phase of forest industry.

Charcoal is produced from wood by pyrolysis (heating wood at high temperatures in the absence of oxygen). Because at best only about one-third of the pyrolyzed wood is obtained as charcoal, the technology is most efficient when the by-product gases and liquids can be collected and used.

In most developing countries, however, wood is converted by the simple covered pile or pit methods, used only to produce charcoal. The process is simple but inefficient. Organic liquids and volatile gases, potentially serviceable as a fuel for combustion engines, are lost. Metal or brick kilns are more efficient, but also more time consuming and costly to build. The still more complicated charcoal retorts needed to collect and recycle gaseous by-products most efficiently are beyond the financial reach of most small producers (Table 4.1).

Charcoal production is attractive when it can be marketed in areas of firewood shortage, where fossil fuel prices are rising, where it is technologically feasible to recover and use by-products, or where transport costs and storage of more bulky firewood make charcoal more economical than wood both as a domestic fuel and as an energy source in small-scale manufacturing.


When a stream of air passes through a bed of red-hot burning wood or charcoal, the oxygen in the air reacts with the carbon in the fire to form carbon monoxide and carbon dioxide. If conditions are adjusted suitably, the proportion of carbon monoxide can be made sufficiently high that the gas can be used as a fuel source in internal combustion engines or directly as a heat source. Gasification can be applied to many uses: the "gasifier" can be used to power stationary engines for irrigation or electricity generation, or can be made compact and portable to operate a car, truck, or boat engine. The technology can fill an important need in supplying fuel for motorized equipment where supplies of petroleum fuel are unavailable or too expensive.*

TABLE 4.1 Characteristics of Charcoal-Making Device






Wood Consumption


(tons per year)

Investment ($US, 1976)

Life (per ton of (years) charcoal)


Earth pile



one firing


Pit kiln



1-2 years


Portable metal



3 years




Brick kiln


(Brazil type)



5 years


Continuous retort



30 years


Source: Hall, Barnard, and Moss, 1981.

Biogas Generation

The production of biogas (principally methane and carbon dioxide) through anaerobic fermentation of organic wastes--crop residues and other plant material and animal and human wastes--provides a means of converting wastes into a useful fuel, while largely retaining their fertilizer value.

The least complex biogas digesters are simple enclosed pits or containers partially filled with water and organic materials. The gas produced by anaerobic fermentation of the organic matter is collected and fed through a tube or pipe to the stove. The digested sludge is periodically withdrawn for use in fields or fish ponds. Larger-scale units that allow for heating, stirring, and continuous addition of organic matter are more complex, considerably more expensive, and require a steady supply of biomass for economic operation.

In addition to producing fuel, biogas generation treats human, animal, and other organic wastes so as to reduce their danger to health. Partially sterilized during fermentation, the residual sludge from the biogas digester contains fewer human and animal pathogens. Plant pathogens in crop residues are less likely to be transmitted to the next year's crop when the digested sludge, having lost little of the nutrient value of the original waste material, is spread on the fields as fertilizer. Through biogas technology, then, a useful fuel is produced, local sanitation is improved, and the soil nutrients are retained.

Biogas technologies have been most widely diffused in Asia, especially in India and China, but also in Korea, the Philippines, and Thailand. They appear to be most readily accepted where fuelwood is in short supply, where there is an abundance of suitable biomass and water not required for other uses, and where there is a tradition of handling and recycling manures as fertilizer. They may also be viewed primarily as a means of nutrient recycling or waste disposal, rather than primarily as sources of fuel. Principal problems with biogas generation technologies derive from their relative structural complexity and cost, consequent difficulties with financing and management, and the specific conditions of substrate C:N ratio, temperature, and pH that they require for maximum gas output.

They are most successfully employed in large-scale integrated waste-recycling systems, and their adoption at the individual household and community level in most parts of the world has been negligible.

Maya Farms in the Philippines is an example of a successful integrated agroindustrial operation. This 24-hectare complex maintains 15,000 pigs, marketing nearly twice that many annually. Every day, 7.5 tons of manure is converted to 400 cubic meters of biogas. The gas is used on the farm for powering deep-well pumps, slurry pumps, a feed mill, and refrigeration units of a packing plant. At night, surplus gas is used to generate electricity.

The liquid effluent from biogas production is used in fish ponds to provide nutrients for tilapia. Digester sludge is used as an ingredient in the pig feed, reducing feeding costs and supplying microbial protein and other nutrients to the diet.*

Alcohol Production

Alcohol fuel can be produced from a variety of biomass forms abundant in developing countries. Sugarcane, sweet sorghum, and numerous cereals and starches, including cassava, can all be used in the microbial fermentation process that produces ethanol. Ethanol is a suitable fuel for lighting and cooking, and it can be used alone to power vehicles or mixed with gasoline as an octane booster. The stillage wastes that are a by-product of alcohol production can be used for animal feed or fertilizer. However, the more common practice of dumping stillage into rivers creates severe pollution problems.

The promise of alcohol fuel production as a renewable energy technology for developing countries lies in the fact that the biomass resources it requires are so widespread. But research is still needed to further reduce the cost of the relatively sophisticated processes required for converting such materials into usable sources of energy on a scale equivalent to petroleum fuels. Most alcohol fuel programs have focused neither on the role of small farmers as producers nor on meeting the energy needs of the rural poor. To date, alcohol fuel diffusion has been very limited. Indeed, only in Brazil is fuel alcohol an appreciable source of energy. However, many countries are now undertaking pilot projects to produce ethanol as a substitute for gasoline, and a few are examining wood gasification as a route to methanol. Methanol production is inherently a large-scale, expensive technology, which is unlikely to supply fuel to the rural or urban poor. Ethanol, on the other hand, is produced almost everywhere as potable spirits and may offer an attractive and economical source of fuel for some developing countries where land is available to grow the substrates, or where ethanol may be the only alternative fuel to keep equipment running in remote areas, or where petroleum fuels are prohibitively expensive.*

But this potential remains to be realized.


Ashworth, J.H., and Neuendorffer, J.W. 1980. Matching Renewable Energy Systems to Village-Level Energy Needs. Solar Energy Research Institute, Golden, Colorado, USA.

De Lepeleire, G., Prasad, K.K., Verhaart, P., and Visser, P. 1981. A Woodstove Compendium. Prepared for the Technical Panel on Fuel Wood and Charcoal of the U.N. Conference on New and Renewable Sources of Energy. Wood Burning Stove Group, Eindhoven University of Technology, The Netherlands.

Hall, D.O., Barnard G.W., and Moss, P.A. 1981. Biomass for Energy in Developing Countries. Pergamon Press, New York, New York, USA.