D. Raw-material supply
The biomass resource endowment in developing countries varies enormously. There are few, if any, reliable and comprehensive data of biomass resources on a country or worldwide basis. There is also the added uncertainty of natural disasters, such as the recent drought in Africa, which might adversely affect the resource.
1. Energy crops
Table 18 gave some indication of the potential contribution to regional energy from biomass grown on “available” land as discussed in section 8.3. It is also interesting to note that, globally, if plantations were established on a total amount of land equivalent to 10 per cent of the area now under forests/woodlands, cropland, and permanent pasture, the annual biomass energy production would be larger than present global consumption of all commercial fuels (oil, gas, coal, hydro and nuclear energy) (Hall et al, 1992b).
Biomass productivities must be improved since they are generally low, being much less than 5 t/ha/yr for woody species without good management (see chapter I). The case studies and Kulp (1990) show that increased productivity is the key to both providing competitive costs and meeting the large feedstock demands biofuel conversion facilities will have. Advances have included the identification of fast-growing species, breeding successes, intercropping and multiple species opportunities, new physiological knowledge of plant growth processes, and manipulation of plants through biotechnology applications, which could raise productivities 5 to 10 times over natural growth rates in trees and microalgae.
It is now possible with good management, research, and planting of selected species and clones on appropriate soils to obtain 10 to 15 t/ha/yr in temperate areas and 15 to 25 t/ha/yr in tropical countries. Record yields of 40 t/ha/yr (dry weight) have been obtained with eucalyptus in Brazil and Ethiopia. High yields are also feasible with herbaceous (non-woody) crops where the agroecological conditions are suitable. For example, in Brazil, the average yield of sugarcane has risen from 47 to 65 t/ha (harvested weight) over the last 15 years while over 100t/ha/yr are common in a number of areas such as Hawaii, South Africa, and Queensland in Australia. Given appropriate R and D efforts it should be possible with various types of biomass production to emulate the three-fold increase in grain yields which have been achieved over the past 45 years although this would require the same high levels of inputs and infrastructure development. However, in trials in Hawaii, yields of 25 t/ha/yr have been achieved without N-fertilizers when eucalyptus is interplanted with N-fixing Albizia trees (De Bell et al, 1989).
Experience has shown that biomass energy plantations are unlikely to be established on a large scale in many developing countries, especially in poor rural areas, so long as biofuels (particularly wood) can be obtained at zero or near zero cost.
2. Existing forests
As shown in chapter 1, wood can be, and is, removed sustainably from existing forests and plantations worldwide by using methods such as coppicing. It is difficult to estimate the mean annual increment (MAI) (growth) of the world's forests. One rough estimate (Openshaw, 1990) is 12.5×109 m3/yr with an energy content of 182 EJ equivalent to 1.3 times the total world coal consumption in 1988. The estimated global average annual wood harvests in the period 1985-1987 were 3.4×109 m3/yr (equivalent to 40 EJ/yr), so some of the unused increment could, conceivably, be recovered for energy purposes while maintaining or possibly even enhancing the productivity of forests (Hall et al, 1992b).
Agricultural residues have an enormous potential for energy production. In favourable circumstances, biomass power generation could be significant given the vast quantities of existing forestry and agricultural residues - over 2 billion t/yr worldwide. This potential is currently under-utilized in many areas of the world. In wood-scarce areas, such as Bangladesh, China, the northern plains of India, and Pakistan, as much as 90 per cent of household energy in many villages comes from agricultural residues. It has been estimated that about 800 million people worldwide rely on agricultural residues and dung for cooking, although reliable figures are difficult to obtain (Leach and Gowen, 1987; Barnard and Kristoferson, 1985). Contrary to the general belief, the use of animal manure as an energy source is not confined to developing countries alone, e.g., in California a commercial plant generates about 17.5 MW of electricity from cattle manure, and a number of plants are operating in the EEC (Rader et al, 1989; Constant et al, 1989).
The energy theoretically available from recoverable residues is about 54 EJ in developing countries and 42 EJ in industrialized regions (see table 19; Hall et al, 1992b). The amount of potentially recoverable residues in table 18 includes the three main sources: forestry, crops and dung. The calculations assume only 25 per cent of the potentially harvestable residues are likely to be used. Developing countries could theoretically derive 15 per cent of present energy consumption from this source and industrialized countries could derive 4 per cent. This is feasible given incentives and efficient conversion, but must encompass environmental sustainability. The table also shows the percentage of land needed, in addition to harvestable residues, to provide all of a region's energy from biomass. It shows that many regions could theoretically achieve energy self-sufficiency by using a relatively small percentage of their total land area, e.g., 2 per cent for Oceania, 3 per cent for South America and 4 per cent for Africa (Hall et al, 1992).
Sugarcane residues (bagasse, and tops plus leaves) - are particularly important and offer an enormous potential for generation of electricity (Ogden et al, 1990; Williams and Larson, 1990). Generally, residues are still used very inefficiently for electricity production, in many cases deliberately to prevent their accumulation, but also because of lack of technical and financial capabilities in developing countries. In many sugarcane-producing countries where cane has been grown for a century or more with increasing yields and good soil maintenance (or even improvement), there are unfortunate commercial pressures to shift away from cane to crops such as cotton which are extremely soil-erosion prone and not nearly as well suited to tropical weather conditions. It is thus important to improve the economic viability of the more environmentally- acceptable cane.
Table 19. Potential energy production from harvestable residues
* Developed Asia = Japan and Israel; Developing Asia = The rest of Asia
Source: Hall et al, 1992a
Depending on the choice of the gas turbine technology and the extent to which barbojo cane tops and leaves can be used for off-season generation, Williams (1989) points out that the amount of electricity that can be produced from cane residues could be up to 44 times the on-site needs of the sugar factory or alcohol distillery. He calculates that for each litre of alcohol produced a BIG/STIG unit would be able to produce more than 11 kWh of electricity in excess of the distillery's needs (about 820 kWh/t). Another estimate of bagasse in condensing-extraction steam turbines (CEST) puts the surplus electricity energy values at 20-65 kWh per ton of cane, and this surplus could be doubled by using barbojo for generation during the off-season. The cost of the generated electricity is estimated to be about $US0.05/kWh (Centro de Tecnologia Copersuca, 1991). Revenues from the sale of electricity co-produced with sugar could be comparable with sugar revenues, or alternatively, revenues from the sale of electricity co-produced with ethanol could be much greater than the alcohol revenues. In the latter instance, electricity would become the primary product of sugarcane, and alcohol the by-product (Williams, 1989).
In India alone, electricity production from sugarcane residues by the year 2030 could be up to 550 TWh/year (the total electricity production from all sources in 1987 was less than 220 TWh (Ogden et al, 1990). Globally, it has been estimated that about 50,000 MW could be supported by currently produced residues. The theoretical potential of residues in the 80 sugarcane-producing developing countries could be up to 2800 TWh/yr, which is about 70 per cent more than the total electricity production of these countries from all sources in 1987 (Williams and Larson, 1992). Studies of the sugarcane industry by Ogden et al, (1990), and of the pulp industry by Larson and Svenningsson (1991) indicate a combined power grid-export capability in excess of 500 TWh/yr. Assuming that a third of the global residue resources could economically and sustainably be recovered by new energy technology, 10 per cent of the current global electricity demand (10,000 TWh/yr) could be generated.
Obviously these are theoretical calculations which gloss over the many country- and site-specific problems to achieving such goals. They do however emphasize the potential which many countries have to provide a substantial proportion of their energy from biomass grown on a sustainable basis.
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