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7 Emerging Technologies to Meet Local Energy Needs The role of energy in catalyzing growth and poverty reduction Small-scale farmers in sub-Saharan Africa (SSA) and South Asia (SA) operate with minimal energy input. Could the availability of greater energy resources transform the lives of farmers? It is not difficult to envision how the energy could be used to increase agricultural productivity. With ad- ditional energy, farmers could power pumps for water supplies and irriga- tion and thus decrease the risks associated with rain-fed systems, increase crop and pasture productivity, and possibly switch to higher-value crops. Mechanization, including the use of small mechanized hand tools, would be possible; it might reduce the burden of cultivation that falls so heavily on women. Manure would no longer be needed for cooking and could be left on the field for fertilization. The presence of alternatives to the use of biomass for fuel would save the time and effort needed to collect firewood, reduce local environmental degradation, and be less polluting. Refrigeration would be possible and could enable better storage of meat, milk, and other products. With energy to power lights, farmers could extend their workday and accomplish more, increasing productivity so that their children would no longer be needed as field workers and would be free to attend school and pursue other activities. Radio, television, and computers would become common mechanisms of obtaining and exchanging information. This chapter examines a number of energy technologies that might be developed to lessen or remove the current reliance on expensive petroleum- based sources of portable energy, such as kerosene and diesel. Energy 211
212 Emerging Technologies to Benefit Farmers technologies are in a state of rapid innovation and growth, and while the committee was in agreement that future energy sources will need to move towards non-petroleum based ones, it was beyond the ability of this study to fully contemplate which of these technologies has the greatest potential to help rural farmers. Applications that are scalable, produce affordable energy, are consistent with the climatic conditions of SSA and SA, and are produced locally might be considered the most appropriate. insufficiency of Electric-Power Grids About 2 billion people (some 30 percent of the worldâs population) lack access to electricity (UNDP, 2004), and about 85 percent of them are the rural poor of SSA and SA (IEA, 2002). Of those 85 percent, half live in SA; India alone is home to one-third (Ailawadi and Bhattacharyya, 2006). In Bangladesh and Pakistan, the proportions of households without access to electricity are 60 percent and 40 percent, respectively (Sarkar et al., 2003). About 600 million people in SSA are without electricity. Oil-rich Nigeria tops the list of African countries with the greatest numbers of electricity-deprived citizens, followed by Ethiopia, Tanzania, Kenya, and Mozambique. The physical infrastructure to provide electricity to the rural poor is lacking, and demand for electricity in urban areas where grids do exist is outpacing the ability to generate power. In early 2008, even South Africa, the only country in Africa with large coal reserves, was experiencing daily blackouts that led to the declaration of a national emergency (Bearack and Dugger, 2008). Electric grids in eastern, western, and central Africa are powered primarily by hydropower and oil- or diesel-fired thermal power. Even with ample rainfall, hydroelectric generating capacity is often inad- equate; with low water levels in lakes and an increasing silting problem in storage structures, more expensive diesel generation is needed for peak- demand management, and blackouts are common. Most countries in SSA and SA have plans to expand power-generation capacity, and a widely recognized high priority is the development of long- range technical planning for these regions to replace the day-to-day crisis management that is the current mode of many energy ministers. Many studies of long-term energy futures for Africa and SA envisage an increas- ingly important role for renewable energy, much of which is site-specific and thus will require local research (Goldemberg et al., 2004; Uddin et al., 2006). Whether new technologies are implemented on or off the grid, trained people who can create them will be needed. In addition, expanded energy services at a local level will probably require a variety of alternative ownership and market structures. These approaches will require an empha- sis on flexibility to identify least-cost options for particular geographical,
Emerging Technologies to Meet Local Energy Needs 213 technological, demographic, and economic situations. Thus, some have advocated for policies geared not toward promotion of specific technolo- gies but toward supporting diverse energy technologies and service-delivery models (Modi et al., 2006). Status of Large-Scale Renewable Energy Projects Among the types of renewable energy options that exist or are being explored for national and regional grid systems in SSA and SA are geo- thermal power, hydropower, wind power, and wave and tidal power. The first three are reasonably established technologies; the fourth is under ex- perimentation. The capital cost of developing all those large-scale resources and building distribution systems for them is high. Because the density of demand in rural areas is low, a lack of grid connections to isolated rural communities is likely to continue for decades. Small-scale farmers outside peri-urban areas are therefore unlikely to benefit from the technologies for some time, but they are briefly mentioned here because they will be impor- tant in the long term to support an industrial base that should be built to complement economic development. Hydropower Hydropower is a mature technology that provides some energy in both SSA and SA. There is strong interest in expanding the number of hydro- power plants in those regions, although the adverse impact of hydropower projects on the environment and their displacement of local populations are continuing concerns, as are the potential effects of silting and droughts on magnitudes of electricity generation. Nevertheless, Chinese companies plan to build a 2-gigawatt (2-GW) plant in the Mambila Plateau in Nigeria in exchange for oil rights. The World Bank recently provided loans for a 250- megawatt (MW) plant on the Nile at Lake Victoria in Uganda and made a US$297 million grant to repair silting at two existing hydropower plants (Inga I and II) on the Congo (World Bank, 2007a,b). The governments and utility companies of South Africa, Botswana, Angola, Namibia, and the Democratic Republic of Congo have formed an alliance to build the worldâs largest hydropower installation on the Congo River. The Grand Inga, as it is known, could generate 39 GW of continuous energy and would cost US$30-80 billion. A final decision about the plan is not expected to take place until 2015, when preliminary studies are complete. If transmission lines are successfully built, the plant could supply electricity to nearly all of Africa and possibly as far away as Europe (IWP&DC, 2007). Hydropower already accounts for almost 25 percent of Indiaâs elec- tricity use, and there are plans to add 16.5 GW of hydropower generating
214 Emerging Technologies to Benefit Farmers capacity by 2012. Because of the demand for electricity, Indian power companies have pursued projects in remote areas of Bhutan and Nepal to produce electricity and export it to India. Wind Power Modern wind-turbine generators are capable of producing more than 1 MW of electricity, and large wind installations have become common in many developed countries. India has the fourth-largest installed wind- energy capacity in the world, with 6.2 GW and growing (BP, 2007). The Indian government has a goal of adding 12 GW by 2012, and there are several turbine-component manufacturers in India, including General Elec- tric. In contrast, SSA has virtually no installed wind power. There are demonstration projects in South Africa, and the coastal areas of South Africa are thought to have the greatest potential for expansion of wind energy in Africa outside the countries in the north (for example, Tunisia and Egypt, which have installed wind-power facilities). Although wind is in most locations an intermittent resource and wind resources are thought to be relatively poor in SSA, little information to support this assumption has been collected. Geothermal Power Geothermal power plants use steam or hot water from geothermal reservoirs to turn turbines. Geothermal energy is the only clean source that can provide firm, predictable power on 24 hours per day, and it is in much greater amounts for a given installation than other renewable sources (Brown and Garnish, 2004). The East Africa Rift Valley is the site of two geothermal electricity projects, and by some estimates the region might be able to provide up to 7 GW, which would double the entire grid capacity of eastern Africa and serve as a buffer to high oil and diesel prices (BP, 2007). Wave and Tidal Power Wave and tidal power is an emerging technology that has lagged in development because of the high relative cost of installation. The World Energy Council has estimated the worldwide wave-power resource to be 2 terawatts (2 TW, or 2,000 GW) (Thorpe, 1999). Among the proposed designs for capturing wave power are oscillating water columns that use the up and down motion of waves to generate electricity, moored floating devices that capture the tension between a fixed point and the movement of the bobbing flotation device, and hinged contour devices that channel
Emerging Technologies to Meet Local Energy Needs 215 waves into an elevated reservoir, whose outflow is used to generate electric- ity. Tidal power is collected by using the cyclic daily movement of currents in and out of shoreline basins to turn turbines (EC, 2008). There are virtu- ally no significant commercial wave or tidal operations worldwide except the 240-MW facility in LaRance, France, built in 1966. The utility of a location for wave power generation depends somewhat on the size of waves. With the exception of southern Africa and the horn of Africa, estimates of wave power density are on the average low (about 15 kW/m of crest length) on African coasts, compared with European coasts (about 50 kW/m) and the Atlantic seaboard (about 35 kW/m). The same is true of much of Asia, but China, India, Korea, and Indonesia are develop- ing offshore energy converters that will exploit breakwaters provided for harbors and local gullies and shorelines formed by steep cliffs that have energetic wave climates (Duckers, 2004). Local Electricity Generation An alternative to national or regional electric grids is the development of small-scale, localized grid networks or stand-alone electricity-generating facilities. These may also be powered by relatively expensive fossil fuels, but there is much interest in using renewable resources, and small-scale hydropower, wind power, solar (photovoltaic) power, and biogas are be- ing used in rural electrification projects in the developing world (Anderson et al., 1999). Small-Scale Hydropower Microscale hydropower installations (300 kW or less) are generally not connected to power grids. These units are ârun-of-the-riverâ installations; that is, they do not use dams or reservoirs to create the energy potential but rather use the natural flow and elevation drop in the river to turn a turbine. Because small-scale hydropower typically does not interfere with river flow, they offer an environmentally benign way to replace diesel gen- erators and to provide energy to rural populations up to a mile from the generator. Microscale hydropower does not provide storage capacity and is vulnerable to supply variations. In the industrialized world, there are many manufacturers of microscale hydropower generators, which come in different designs for different water-flow conditions. The technology is very scalable, although the larger the system, the more skilled maintenance is required. The cost of microscale generators is about US$200-500 per kilo- watt of capacity. Local industry could be developed to produce small-scale systems, such as the tiny Peltric turbo generator (basically a series of cups
216 Emerging Technologies to Benefit Farmers attached to a hub), which is able to produce 1 kW of power and has been used in many countries (Ramage, 2004). There seems to be little information on the overall potential for sites, but some applications that are in place are potential models, such as a 60-kW system installed in a rural hospital in western Uganda at a cost of US$15,000. In Malawi, a 600-kW system installed in the 1920s is still in operation (Zachary, 2007). Small-Scale Wind Power Small-scale wind generators for supplying electricity for battery- charging, stand-alone applications, and connection to small grids are evolving. The U.S. Department of Energy (DOE) recently announced that it had met its goal of reducing the cost of residence-size wind turbines (less than 10-kW capacity) to US$0.10 per kilowatt-hour and the cost of small village-size turbines (less than 100-kW capacity) to under US$0.11 per kilowatt-hour (DOE, 2008). Small wind generators in the 1-kW range might be built locally with a variety of available materials, such as laminated wood, steel, and plastics. But the efficiency and reliability of the device depend on the design of the foils and on the engineering of the electronics. Among DOE partners, the most cost-competitive microscale design so far is a 1.8-kW design that costs US$5,500 (not including installation) and that the manufacturers estimate could provide 100,000 kW-h over a 20-year life span (DOE, 2008). An ac- curate map of the prevailing wind speeds in SSA and SA on the scale needed to determine the viability of small wind generators is, to the committeeâs knowledge, unavailable, but obtaining such information would have to be a preliminary step in estimating the utility of these devices. If the technol- ogy were practical and the market were large enough, there would be value in developing the technology for use in rural areas and establishing local manufacturing capacity. Solar Power Concentrated Solar (Thermal) Energy Solar cookers collect heat from sunlight and provide energy for boiling and cooking, reducing the use of firewood and the pollution associated with burning of wood. They typically consist of a small number of reflectors (or a parabolic mirror) focused on an oven box. Parabolic solar cookers with a diameter of 1 m are large enough for a family; in India, solar cookers supply boiling water for a kitchen serving more than 1,000 people. A num- ber of projects scattered throughout SSA and SA distribute solar cookers
Emerging Technologies to Meet Local Energy Needs 217 produced in China. Solar cookers function only during the day (and are therefore used as a supplement), and, like other improved cookers, they are not always accepted by recipients. However, these projects have consider- able potential for expansion (SCI, 2007). Solar heat can produce electricity if parabolic troughs are used to focus solar radiation on the heating chamber of a Stirling engine (Box 7-1 and Figure 7-1) or a heat exchanger coupled to a steam engine. This technology might have particular relevance for arid and semi-arid regions in Africa (Everett, 2004). However, it is in large-scale applicationsâsuch as the 64- MW, 300-acre power plant opened in 2007 near Las Vegas, Nevadaâthat the efficiency of sunlight-to-electricity conversion can reach 40 percent as the heat generated by the mirrors reaches 750Â°F. The Nevada plant cost US$250 million to build and is expected to provide power for a half-million people at an approximate cost of US$0.09-0.13 per kilowatt-hour. The BOX 7-1 Stirling Engine In contrast with the industrialized world, SSA and SA have a need to reliably produce power in the range of 500 to 5,000 W for small rural communities at low cost. Diesel generators are typically used to power small grids for rural com- munities, but diesel is an increasingly expensive source of energy, and diesel generators break down often. A more robust source of energy is provided by the Stirling engine, which uses a technology that is more than 100 years old. Stirling engines work on the principle of a thermodynamic cycle in which a gas or liquid in a cylinder is heated so that it expands (driving a piston to perform work), then undergoes cooling and isothermal compression before the cycle is repeated. The engines, of which there are multiple designs and scale, can be more energy-efficient, quieter, and more reliable and require less maintenance than an internal-combustion engine, although they are initially more expensive (Andrews and Jelley, 2007). It is par- ticularly important that they can generate electricity from heat-producing energy sources, such as solar thermal energy or combusted agricultural waste and domestic refuse. Stirling engines can be directly coupled with mechanical power to pump water and perform other mechanical applications. NASA has recently called attention to a modernized version of the Stirling engine manufactured by Lockheed Martin and Sunpower that achieves more than 35 percent efficiency (Shaltens and Wong, 2007). The modern Stirling engine can be powered by solar energy with concentrators, radio isotopes, or combustion of wastes, coal, or agricultural disposals. The design of this engine is intended for space applications but could be adapted for terrestrial use.
218 Emerging Technologies to Benefit Farmers FIGURE 7-1â Schematic of a Stirling engine. SOURCE: MIT, 2008. Reprinted with permission. Â© 2008 by Katie Byl, Massachu- setts Institute of Technology. 7-1.eps bitmap image goal for larger projects is to bring the cost down to US$0.07 per kilowatt- hour (Broehl, 2006). Building a plant of that size requires substantial land and presumes the existence of an electric grid. Recently, plans to develop smaller-scale applications of the technology were announced (LaMonica, 2008). Although little information on smaller systems was available, the cost per kilowatt-hour would certainly increase. Nevertheless, given the abundance of solar energy in SSA and SA and the relative simplicity and low maintenance of such a system, the technology warrants further explora- tion. Solar concentrators can also be used with photovoltaic electric cells, as described in the next section. Photovoltaic Energy Conventional solar photovoltaic (PV) technology uses silicon-based semiconductors to convert photons directly into electricity at an efficiency of up to 22 percent. The efficiency of PV technology is limited in part by the âdensityâ of solar energy reaching Earth. The sun radiates energy at about 1 kW/m2 of Earthâs surface; every square mile receives about 2.6 GW. One way to overcome that limitation is to concentrate the solar energy with mirrors, Fresnel lenses, and other devices that are typically placed above the solar cells. The benefit is increased conversion efficiency; as a result, less silicon (which is expensive and of limited availability) needs to be used to generate the same amount of electricity, and the cells cost much less. The drawback is that cooling mechanisms are needed to prevent the
Emerging Technologies to Meet Local Energy Needs 219 concentrators from overheating the cells. Concentrator systems are being tested around the world. PV technology is ideally suited for meeting low demands for electricity. The current cost is relatively high, howeverâabout US$8 per watt. Thus, one estimate is that a 10-kW system (which would be considered a large residential or small industrial system by U.S. standards) installed in 2007 would cost about US$80,000 (Borenstein, 2008). Solar-cell technologies are diversifying rapidly, and waves of innova- tions are focused on reducing cost and increasing conversion efficiencies. A second-generation technology (thin-film cells) reduces the amount of mass in a cell by using new light-absorbing materials (inorganic materials, dyes, and organic polymers). A third generation is based on nanocrystals (such as quantum dots) that generate and capture, at different levels of excitement, electrons that would ordinarily be lost in silicon systems; experimental cells of this type are approaching 40 percent conversion efficiency and would push the costs of PV cells down dramatically (Nozik, 2005). However, reductions in other system components are just as important. The International Energy Agency (2006) summarized the potential of solar PV technology as huge, but at current rates the research and learning ef- forts needed to bring costs down to competitive levels could approximate US$100 billionâmuch higher than the cost for any other renewable re- source technology. Energy Storage Emerging innovations in energy storage are highly relevant for the poor farmer in SSA and SA. First, they could reduce the costs and improve the efficiency of the current form of energy storage in use by the rural poor in these regionsâbatteries. In Uganda, where more than 80 percent of the population lives on US$1 a day, more than US$100 million is being spent each year on small, disposable dry-cell batteries for radios and lighting. Car batteries are used for other applications and are brought into town for recharging with a diesel generator. Second, energy storage has a role in maximizing the benefits of off-grid solar, hydro, and wind power, which are inherently intermittent. If excess power generated when operating condi- tions are favorable could be stored, energy would be available when operat- ing conditions reduce generating capacity. One practical way to store energy is in the form of pumped water. Ja- pan uses this method in conjunction with nuclear-power stations. It pumps water from a low reservoir to an upper reservoir when electricity demand is at its lowest; during peak demand, the water is discharged back to the lower reservoir and drives a turbine to generate electricity (Ramage, 2004; Andrews and Jelley, 2007).
220 Emerging Technologies to Benefit Farmers For a number of reasons, this is a good time to look for energy-storage solutions for small-scale farmers. Consumer-products manufacturers are in a race to miniaturize components, and hybrid-vehicle manufacturers are seeking to build lighter and less expensive batteries. As interest in renew- able energy sources has grown, so have ways to increase their efficiency with energy storage. Batteries store electricity in the form of chemical energy. A battery consists of two electrodes made of materials that have different chemi- cal potentials with an electrolyte between them. When the electrodes are connected to a device, electrons flow through the device toward the more positive electrode, and ions move in both directions through the electrolyte. Lithium-ion batteries, first introduced in 1991, are rechargeable because ions of the same type, Li+, move from each electrode through the electro- lyte and are simultaneously extracted from and inserted into each electrode (Armand and Tarascon, 2008). The energy-storage capacity of lithium-ion batteries is about five times higher than that of older lead-acid batteries and three times higher than that of conventional nickel-cadmium batteries. More than 2.4 billion bat- teries a year are produced for laptop computers and related devices. The shortcomings of current lithium-ion batteries include safety issues (fires due to runaway reactions), relatively low power output, and the fact that they ultimately lose their ability to be recharged (Scrosati, 2007). In addition, some of the battery components are mineral (cobalt or magnesium) ores that exist in scarce quantities and must be mined (Armand and Tarascon, 2008). They are also more expensive than conventional batteries, so people in rural parts of Africa are less likely to purchase them despite being reus- able (Anand Gopal, University of California at Berkeley, presentation to committee, July 6, 2007). Capacitors are conventionally used to provide a burst of electricity during the startup of a piece of electric equipment. Supercapacitors (also called electric double-layer capacitors or ultracapacitors) are more effi- cient and consist of two activated-carbon electrodes, an electrolyte, and a porous separator that permits the flow of ions but not electrons between the electrodes. When a current is passed across the electrodes, ions from the electrolyte are absorbed into the pores of both oppositely charged electrodes and are stored there. The storage of energy is electrostatic and not chemical, as in batteries; as a result, supercapacitors can both store and deliver energy rapidly. Their widely scalable storage capabilities make it possible to use them in conjunction with other devices, such as batter- ies and fuel cells (NRC, 2007). The benefits of supercapacitors are that they have a virtually unlimited life (they can be charged and discharged millions of times); they recharge in seconds, not hours; and they cannot be overcharged. Their limitations are that they discharge all their energy
Emerging Technologies to Meet Local Energy Needs 221 relatively quickly, can provide only rather low voltage, and until recently could not store electric energy very densely. For small applications and as a backup for short bursts of energy, a small supercapacitor could suffice; but for an electric car that otherwise runs on 400 kg of lead-acid batteries, a supercapacitor would have to weigh 8 tons (Okamura, 2004). Batteries and capacitors are changing rapidly, and the two technologies are converging. Much of the change is being propelled by the manufac- ture of nanomaterials. In particular, the ability to make multiwall carbon nanotubes (MWCNs) promises to help supercapacitors to overcome their storage-density limits. Storage density is directly related to the amount of surface area of the electrodes and their pores where ions are absorbed. The electrodes of current supercapacitors are made of activated carbon, an amorphous material with nonuniform pores. In contrast, MWCNs are tightly packed, evenly spaced, vertically aligned strands (tubes). Packed together as viewed with an electron microscope, they collectively look like a paintbrush. Each 5-nm-wide strand of the brush is an electrode, so in the same space as activated carbon the MWCNs provide much more electrode surface area and, as a result, much greater storage capacity (Signorelli et al., 2004). A recent breakthrough achieved in a seemingly simple fashion com- bined MWCNs with partially dissolved cellulose to make a highly flexible nanocomposite âpaperâ that functions as a superthin (less than 100 Î¼m) supercapacitor with highly improved storage capacity and voltage. If a thin layer of lithium is deposited on one side of the nanocomposite paper, the device can act as a rechargeable battery. The two configurations can be used together as hybrids that have the desirable features of both batteries and supercapacitors (Pushparaj, 2007). The greatest hurdle that this technology faces is the cost of producing the MWCNs, although if production were scaled up costs would drop substantially (Scrosati, 2007). There are many emerging approaches to batteries, for example, using biochemical processes to generate electricity and even using air as a chemi- cal reactant in a lithium-oxygen or zinc-air device. The question for all of them is whether they can be developed into applications that meet the needs of small-scale farmers and rural communities. If they are to do that, the potential spectrum of the applications needs to be defined firstâfrom rechargeable hand tools and small-farm equipment or vehicles to energy storage for the village-scale wind turbine. Coupling an understanding of the requirements for those applications with a plan for producing storage devices with the right specifications could move off-the-shelf applications to farmers much faster than the market normally would. Given the impor- tance of stand-alone sources of energy and energy storage to rural farmers, helping to make these technologies more feasible and affordable warrants further research and commercialization.
222 Emerging Technologies to Benefit Farmers Hydrogen and Fuel Cells Hydrogen can be converted to electricity by using fuel cells. Fuel cells generate electricity or store energy in the form of hydrogen or other metals such as zinc or aluminum, and they provide carbon-free electricity with very low emissions, efficiencies of around 50 percent, and flexibility in that power output can be changed very quickly. They are currently expensive for routine use in developing countries, but this could change inasmuch as research is very active (Boyle and Everett, 2004). Hydrogen and metallic fuel cells have been widely advocated as an âenergy carrierâ for the future, but any practical scheme for large-scale use of hydrogen or other metals would require many steps, including storage and distribution facilities that require capital investments (Boyle and Everett, 2004). Hydrogen is made now mostly from methane or natural gas, and the processes generate carbon dioxide (CO2). Metals such as zinc and alumi- num require significant electrical power to refine them from ore or the resulting oxide from battery use. In addition, in current market conditions, the 50 kWh of electricity consumed in the manufacture of 1 kg of hydrogen is roughly as valuable as the hydrogen produced, assuming US$0.08 per kilowatt-hour. However, many technologies that use renewable energy are being developed for hydrogen or metal generation; they are often suitable for local production, and Africa seems well suited to exploit several of them. The gasification of biomass produces large quantities of hydrogen and leaves behind a residue of high-grade carbon that can be used for chemical purposes and carbon that is likely to end up as CO2 that can be reabsorbed if the biomass is sustainably grown (Larkin et al., 2004). Metal- lic âcyclesâ do not have the problem of CO2 generation. The desert regions of Africa seem optimal for the thermal dissociation of water into hydrogen and oxygen with solar collectors (Steinfield, 2005). Hydrogen can also be produced by direct electrolysis of water; this process could be used to produce hydrogen virtually anywhere from renewable energy: solar power in the deserts, wind power, hydropower, or geothermal energy (Everett and Boyle, 2004). Water can also be split by artificial chemi- cal photosynthesis with photoelectrochemical cells; laboratory tests have confirmed the efficiency of this procedure, but there are problems, including corrosion of the semiconductors. Finally, the biological-energy production team of the J. Craig Venter Institute is focusing its efforts on biological production of hydrogen by recombinant cyanobacteria (Xu et al., 2005). Biofuels The production of liquid fuels from biomass is controversial worldwide for a number of reasons. One is that growing the feedstock competes with
Emerging Technologies to Meet Local Energy Needs 223 food production. For example, some economic analyses have suggested that if cassava were used as a major source of biofuel, food cassava prices could double or triple (Rosengrant et al., 2006). A second is that, depending on how it is produced, the energy from biofuels can vary widely. In SSA and SA, the starch encompassed in seed is more highly valued for food and ani- mal feed. If agricultural productivity in those regions could be increased to world averages, land might be available for biofuel production. Cellulosic Ethanol Conversion of the vegetative tissues of plants into sugars or hydro- carbons can produce much more energy than conversion of seeds. The cell walls of plants and trees constitute the greatest amount of biomaterial on the planet. Plant cell walls consist of cellulose and hemicellulose fibrils intertwined with complex lignin molecules. During plant development, the chemical composition of cell walls varies from tissue to tissue within a species. The differences involve the length of cellulose and hemicellulose chains, the size and amount of lignin complexes, and thus the amount of constituent monomers. The amounts of inorganic molecules also differ, and this affects downstream processing of the plant material. There are two general approaches to generating fuels from biomass: 1. The enzymatic conversion of the cellulose and hemicellulose in the biomass to sugars, followed by the fermentation of sugars to ethanol, butanol, or other alcohols. 2. A thermochemical step that involves pyrolysis of the biomass to make, for example, syngas (carbon monoxide and hydrogen) and conver- sion of these molecules to hydrocarbons of various sorts via Fischer-Tropsch synthesis. Substantial investment and research are devoted to exploring different versions of those technologies to find the most efficient and cost-effective. Cellulosic fuel technologies will likely be cost-efficient by 2015. Many areas of SSA and SA would be suitable for high biomass pro- duction, but the issue of whether land is to be devoted to energy or food production remains. Biomass from existing crop residues is available in all countries, but it is used for many purposes, including the important main- tenance of soil fertility, which should not be sacrificed for fuel production (Doornbusch and Steenblick, 2007; Lal, 2007). The use of land that is marginalâthat is, of poor quality for food productionâhas been proposed for growing biofuels. Warm-season, C4 grassesâsuch as kallar grass, guinea grass, and elephant grassâmight be candidates for energy production in SSA and SA. Sweet sorghum hybrids are particularly attractive sources of
224 Emerging Technologies to Benefit Farmers biofuels because they produce grain and sugar-rich stalks, and they produce more biomass, are more widely adapted, grow faster, and require less water than corn or sugar cane. As described in Box 7-2, there are many pos- sible ways to make sweet sorghum, tropical trees, and grasses even better adapted for high biomass growth in various environments. Selected species need to be genetically selected for high biomass production and favorable energy-production ratios, and they should be the focus of modern breeding programs (discussed in Chapter 3). A biofuel industry in SSA and SA can be considered appropriate only after food productivity increases so that it will not destabilize food produc- tion. Many of the crops proposed for biofuels would perpetuate subsistence BOX 7-2 Breeding for Biofuels and Forage Biomass for energy needs to be grown at high density to reduce transport costs, especially if it is not processed on the farm. Thus, biomass yield, incor- porating high photosynthesis and optimal plant architecture, is a key trait for a breeding program. To sustain high yields, many improvements in crop-protection traitsâsuch as drought and salt tolerance, disease resistances, and heat resis- tanceâare also very important. Because the biomass needs to be processed in some way, the real yield is metric tons of fuel or energy per acre. Therefore, the plant breeder needs to improve traits that affect the chemical composition of energy crops to be commensurate with downstream processing technologies. If the biomass is to be digested in an enzymatic process, it is desirable to breed for cell wall lignocellulose structures that are easily degraded by digestive enzymes. Today, a major cause of difficulty and cost is the pretreatment step applied to biomass before enzymes can efficiently degrade the cellulose and hemicellulose to sugars. It is possible to breed plants with reduced lignin and with different cell wall chemical structures that are easily degraded by enzyme cocktails or microorganisms. That has been achieved by forage crop breeders who assay plants for digestibility by enzyme systems characteristic of animal digestive systems. There is a synergy between alternative uses of biomass on the farm. However, producing plants whose cell walls are easier to degrade often creates deficien- cies that can result in reduced yields and increased susceptibility to pests and diseases. Thus, a balance has to be struck between yield and efficient cell wall degradation. The interest in cell wall biology in the United States that is being driven by the biofuels industry is likely to bring a new understanding of the lignocellulose complexes of plants and trees and aid in defining crop breeding objectives for processing to sugars for both biofuels and animal-feed purposes.
Emerging Technologies to Meet Local Energy Needs 225 farming. Thus, biofuel production should be considered only if the biofuel crops produce sufficient revenue for rural communities, either from sale of the biomass or from additional employment in the biomass-to-energy sector. There can be many forms of such an industry. In some cases, the feedstocks could be regionally centralized if the transport costs were not too high and if centrally located biorefineries were built to process the biomass. In other cases, the biomass would be converted locally to supply local needs. Halophytes Halophytes appear to constitute a promising and relatively unexplored option for growing biofuel feedstocks that do not compete with scarce food-producing resources. Halophytes are salt-loving plants that grow in or with brackish water that most crops cannot tolerate. Halophytes with multiple uses include pickle weed and nypa forage (Salicornia spp.), salt grass (Distichlis spp.), saltbush (Atriplex spp.), and some algae (Spirulina spp.). The oilseed halophyte Salicornia bigelovii produces 2 tons of seed per hectare and fractions of oil and meal that are similar to soybeans (Glenn et al., 1999). Studies with Atriplex spp. and Marianna spp. in Pakistan showed high tolerance for salt, sodic, and waterlogged soils (Asad, 2002). Other halophytes with a high biomass-producing capacity include Batis spp., Suaeda spp., and Sesuvium spp. (Lal, 2001). Although those plants would seem to have applications in SSA and SA, most of the research on halophytes is taking place in Australia, which has a long-standing interest in halophytes for forage and for their potential to remediate saline soils (Barrett-Leonard, 2002). Oilseeds Jatropha curcas is probably the most highly promoted oilseed crop for biodiesel production in the developing world (Fairless, 2007). Immature fruits are harvested by hand in the dry season (winter) when the leaves have fallen; then they are dried in the shade, and the seeds are removed by hand. Common names for the nutâsuch as black vomit nut, purge nut, and physic nutâand for its oil, such as hell oil and oil infernale, refer to the plantâs toxicity. The seeds contain alkaloids and curcin, a toxalbumin with similar sequences and similar oral toxicities to ricin (IPCS, 1990, 1994). The oil contains irritant and cancer potentiators or synergists: curcusones are diterpenoids of the tiglian (phorbol) type. The best removal procedures eliminate about half the phorbol esters (Haas and Mittelbach, 2000), and this is toxicologically unacceptable. Castor bean (Ricinus communis) pollen contains numerous allergens, including some that are very common (such as latex allergens) and others
226 Emerging Technologies to Benefit Farmers that are found in poisonous seeds (Singh et al., 1997; Parui et al., 1999; Palosuo et al., 2002). Ricin, a toxalbumin, is the most toxic protein in the seeds (IPCS, 1990). When present at a low concentration, the ricin in the residue from manufacture of 50 L of biodiesel (a typical small-vehicle fuel- ing) is sufficient to kill about two average-size people, and 30 people could be killed at the highest ricin concentrations. No antidote, vaccine, or other therapy is available for ricin poisoning, although attempts have been made to develop a vaccine against it (Griffiths et al., 2007). After the seeds of Jatropha and castor bean are crushed for oil, the high-protein residue typically is spread on fieldsâa practice of question- able environmental safety and health. Removing the toxic compounds from these oilseeds might allow the residue to be safely used for animal feed. This is similar to the uses of soybean meal, which is both a high-quality animal feed and human food. Even with the recent demand of the oil for biodiesel, the value of the meal as a portion of the total value of soybean is greater than that of its edible and combustible oil. Some Jatropha germplasm accessions have been found to be less poi- sonous than others (Makkar et al., 1998) but still too toxic for use as fod- der. Castor bean varieties that are low in ricin and the related agglutinin have been bred, but they are still too toxic to be usable as feed (Auld et al., 2003). Jatropha can be transformed with transgenes and regenerated (Li et al., 2006). There are a number of possible strategies for interfering with Jatropha phorbol ester production, such as by antisense or RNAi suppres- sion of genes in the phorbol ester biosynthesis pathway (Gressel, 2008). The gene for curcin, the toxin in Jatropha, has been cloned and the protein purified (Lin et al., 2003). The ricin gene from castor bean also has been se- quenced (Tregear and Roberts 1992), and castor bean has been transformed and regenerated (McKeon and Chen 2003; Sujatha and Sailaja, 2005; Malathi et al., 2006). Curcin and ricin production could be suppressed by partial gene deletion with chimeraplasty surgery, a technology that uses RNA constructs to modify a gene without leaving a trace of recombinant material (Zhu et al., 2000). By creating transgenic varieties of Jatropha curcas and Ricinus communis that are non-toxic to humans and animals, these transgenic varieties would be safe for humans and the environment and could be valuable for biofuels and animal feed. The removal of those toxins might make the plants more vulnerable to attack by insects and pathogens, but in one experiment this was counteracted by the addition of the Bt gene in the transformation cas- sette to control the castor semilooper (Malathi et al., 2006). Other genes unrelated to the toxins would be helpful in domesticating the species. For example, Jatropha could be bred or modified for mechanical harvesting, just as breeding of castor bean has led to machine-harvestable
Emerging Technologies to Meet Local Energy Needs 227 varieties. Genes would have to be found that control shattering so that ripe seeds do not fall before harvest (Gressel, 2008). Photosynthetic Microbes: Algae and Cyanobacteria In the 1980s and 1990s, DOEâs Aquatic Species Program explored the potential use of algae to make liquid fuels and decided that it was impracti- cal because the growth of algae in open ponds was ruined by contamination from local microorganisms and the alternative, a closed bioreactor system, was too expensive to build and operate. Although the test sites met their goals of algae production, temperature fluctuations at night at the desert test site in New Mexico adversely affected the project. Nevertheless, when the project ended in 1996, the participants concluded that there was great potential for algae and that the main hurdle was the cost of production relative to the price of petroleumâUS$70 per barrel versus what was then US$25 per barrel of fossil petroleum (Sheehan et al., 1998). There has recently been a modest revival of interest in the microbial production of biofuels in the United States, but it is in sunny, warm locations where the best natural conditions for growing photosynthetic microbes exist. Algae and cyanobacteria, their prokaryotic forerunners, have several properties that make them promising for biodiesel production. First and foremost, algae species (Botryococcus, Dunaliella, Scenedesmus, and Prym- nesium) can produce and accumulate more than 60 percent of their biomass as lipid (Becker, 1994). Some of the cyanobacteria, such as Synechocystis sp. 6803, have multilayered cell membranes that contain lipids. They can also be fed high concentrations of CO2 from industrial flue gases without inhibition. The production of oil by photosynthetic microbes substantially outperforms other oil crops (Table 7-1). Another feature of the organisms is that they have relatively simple growth requirements: water, sunlight, CO2, and nutrients, such as nitrogen and phosphorus. Many of the organisms can tolerate saline or brackish TABLE 7-1â Comparison of Lipid Production by Oil Crops and Microbes Organism Lipid Production (L/ha per year) Microbes 72,000-130,000 Oil palm 4,000 Jatropha 2,700 Sunflower 570-1,030 Soybean 380-650 SOURCE: Courtesy of W. Vermaas (adapted from Huber et al. 2006 and incorporating data from W. Vermaas presentation to the committee in October 2007). Reprinted with permission. Â© 2007 by Willem Vermaas.
228 Emerging Technologies to Benefit Farmers water, and most of the water used to grow them can be recycled. Finally, a byproduct of oil production is a residue that is potentially useful as animal feed. Although algae produce oils at higher rates than cyanobacteria, oil pro- duction in algae appears to be inversely proportional to growth, so the al- gae double at a rate of only 0.6 times per day. Lipid production is triggered by environmental stress, so biofuel production is a survival mechanism. As a result, continuous oil production under stressed conditions eventually re- sults in overall slower growth. Cyanobacteria are more easily manipulated with molecular biology, and the same evolutionary forces play a role in the growth of large amounts of the organism over time. Research on these microorganisms is assisted by the fact that the full genome sequences of several algae and cyanobacteria are available (NCBI, 2008). It is possible to grow algae and cyanobacteria in open ponds, but ul- timately, because of microbial contamination and the large parcels of land needed to increase the surface area exposed to solar radiation, relatively simple bioreactors can be devised. Plants evolved to take full advantage of sunlight can be grown erect, capturing not only direct sunlight but sunlight that is filtered or reflected by other plants before it reaches the ground. This upright design concept has been incorporated into sunlight-driven algal bioreactors to maximize the yield of biomass per acre of land. Closed bioreactors provide additional benefits, including physical containment and exclusion of microorganisms, convenient delivery of concentrated CO2 to accelerate algal growth, facilitated harvest of biofuels from the organisms, the ability to reuse and recirculate water in the production system, and scalable modularity to support both large-scale and small-scale systems. To provide a controlled source of CO2 for the plants, a bioreactor would be ideally constructed as an adjunct to a power plant, brewery, or other CO2- emitting facility. However, some argue that because of the higher capital costs, the ideal design is to use simple closed bioreactors to feed open or covered ponds. Federal and state sources funded substantial programs of algae cultiva- tion in Hawaii during the 1990s. Bioreactors were developed to produce commercial quantities of astaxanthin for fish feed and medicinal applica- tions. The enclosed bioreactors were also used in conjunction with open-air ponds aided by solar radiation. The technical needs for developing photosynthetic microbes further for biofuels include the selection (or molecular design) of oil-producing organ- isms that are highly efficient in using light, can operate at temperatures where they will be used, and are readily amenable to biofuels extraction and processing; the ability to provide a high concentration of CO2 in the liquids in which the organisms are growing; the availability of a secondary market for the residue; and an efficient bioreactor design.
Emerging Technologies to Meet Local Energy Needs 229 Although the product is liquid that is de-esterified to produce diesel, it obviously can be combusted for electricity generation. The availability of molecular tools for increasing the efficiency of organisms, the flexibility of the technology with regard to scale, and the suitability of climates in SSA and SA make a convincing case to further pursue this unique opportunity. Other Technologies The committee was unable to examine all of the technological pos- sibilities for energy production, including for example, manure bio-gas generators now used in rural farms in many parts of the world. Other types of technology not examined by the committee were innovations related to farm machinery. The replacement of rudimentary tools, such as the hoe, for mechanized tools that facilitate on-farm operations (ploughing, planting, weeding, drying, processing, storage) and reduce the drudgery of farming is likely to be a fertile area for innovation. However, mechanized technologies depend on an energy source, so these applications should be co-developed in combination with rechargeable batteries or capacitors. These and other energy technologies deserve further attention. References Ailawadi, V. S., and S. C. Bhattacharyya. 2006. Access to energy services by the poor in India: Current situation and need for alternative strategies. Nat. Resour. Forum 30(1):2-14. Anderson, T., A. Doig, D. Rees, and S. Khennas. 1999. Rural energy services: A handbook for sustainable energy development. London, UK: IT publications. Andrews, J., and N. Jelley. 2007. Energy Science, Principles, Technologies and Impacts. Ox- ford, UK: Oxford University Press. Armand, M., and J. M. Tarascon. 2008. Building better batteries. Nature 451:652-657. Asad, A. 2002. Growing Atriplex and Maireana species in saline sodic and waterlogged soils Commun. Soil Sci. Plant Anal. 33(5-6):973-989. Auld, D. L., S. D. Pinkerton, E. Boroda, K. A. Lombard, C. K. Murphy, K. E. Kenworthy, W. D. Becker, R. D. Rolfe, and V. Ghetie. 2003. Registration of TTU-LRC castor germ- plasm with reduced levels of ricin and RCA(120). Crop Sci. 43:746-747. Barrett-Lennard, E. G. 2002. Restoration of saline land through revegetation. Agric. Water Manag. 53(1-3):213-226. Bearak, B., and C. W. Dugger. 2008. Power failures outrage South Africa. New York Times. Jan- uary 31. Available online at http://www.nytimes.com/2008/01/31/world/africa/31safrica. html [accessed March 21, 2008]. Becker, E. W. 1994. Cambridge Studies in Biotechnology, Vol. 10. Microalgae: Biotechnology and Microbiology. Cambridge, UK: Cambridge University Press. Borenstein, S. 2008. The market value and cost of solar photovoltaic electricity production, CESM Working Paper 176. Berkeley, CA: University of California Energy Institute. Boyle, G., and B. Everett. 2004. Integration. Pp. 384-439 in Renewable Energy: Power for a Sustainable Future, 2nd edition, G. Boyle, ed. Oxford, UK: Oxford University Press.
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