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Chapter 12. Turning to Renewable Energy: Plant-Based Sources of Energy
As oil and natural gas reserves are being depleted, the world’s attention is turning to plant-based energy sources. These include forest industry byproducts, sugar industry byproducts, urban waste, livestock waste, energy crops, crop residues, and urban tree and yard wastes—all of which can be used for electrical generation, heating, or the production of automotive fuels.
In the forest products industry, including both sawmills and paper mills, waste has long been used to generate electricity. U.S. companies burn forest wastes both to produce process heat for their own use and to generate electricity for sale to local utilities. The bulk of the nearly 10,000 megawatts in U.S. plant-based electrical generation comes from burning forest waste. 76
Wood waste is also widely used in urban areas for combined heat and power production, with the heat typically used in district heating systems. In Sweden, nearly half of all residential and commercial buildings are served with district heating systems. As recently as 1980, imported oil supplied over 90 percent of the heat for these systems, but by 2005 it had been largely replaced by wood chips, urban waste, and lignite. 77
In the United States, St. Paul, Minnesota—a city of nearly 300,000 people—began to develop district heating more than 20 years ago. It built a combined heat and power plant using tree waste from the city’s parks, industrial wood waste, and wood from other sources. The combined heat and power plant, using 250,000 tons or more of waste wood per year, now supplies district heating to some 80 percent of the downtown area, or more than 1 square mile of residential and commercial floor space. This shift to wood waste largely replaced coal, thus simultaneously cutting carbon emissions by 76,000 tons per year, disposing of waste wood, and providing a sustainable source of heat and electricity. 78
The sugar industry recently has begun to burn cane waste to cogenerate heat and power. This received a big boost in Brazil, when companies with cane-based ethanol distilleries realized that burning bagasse, the fibrous material left after the sugar syrup is extracted, could simultaneously produce heat for fermentation and generate electricity that they could sell to the local utility. This system, now well established in the Brazilian ethanol industry, is spreading to sugar mills in other countries that produce the remaining 80 percent of the world sugar harvest. 79
Within cities, once recyclable materials are removed, garbage can also be burned to produce heat and power. In Europe, waste-to-energy plants supply 20 million consumers with heat. Germany, with 65 plants, and France are the European leaders. In the United States, some 89 waste-to-energy plants convert 20 million tons of waste into power for 6 million consumers. 80
With U.S. livestock and poultry production now concentrated in large facilities, the use of animal waste in anaerobic digesters to produce methane (natural gas) is catching on fast. AES Corporation, one of the world’s largest electrical power companies, is creating a business of capturing methane from animal waste. Using biodigesters, AES contracts with farmers to process their animal waste, producing methane and a nutrient-rich solid waste that farmers return to the fields as fertilizer. The methane collected in these generators can be burned to supply heat and generate power. 81
Corporations and utilities are also tapping the methane produced in landfills as organic materials in buried garbage decompose, to produce industrial process heat or to generate electricity in combined heat and power plants. Interface—the world’s largest manufacturer of industrial carpet—near Atlanta, Georgia, convinced the city to invest $3 million in capturing methane from the municipal landfill and build a nine-mile pipeline to an Interface factory. The natural gas in this pipeline, priced 30 percent below the world market price, meets 20 percent of the factory’s needs. The landfill is projected to supply methane for 40 years, earning the city $35 million on its original $3 million investment. For Interface, operating costs are reduced and it gains an offset of its greenhouse gas emissions, thus enabling the factory to become climate-neutral. 82
Crops can also be used to produce automotive fuels, including both ethanol and biodiesel. In 2007 the world produced 13.1 billion gallons of fuel ethanol and 2.3 billion gallons of biodiesel. Half of the ethanol came from the United States, a third came from Brazil, and the remainder came from a dozen other countries, led by China and Canada. Almost one fourth of the biodiesel was produced in Germany; the other major producers were the United States, France, and Italy. 83
The United States, which surged ahead of Brazil in ethanol production in 2005, relies heavily on corn as a feedstock. With U.S. ethanol production projected to nearly double between 2007 and the end of 2008, U.S. output will jump to 13 billion gallons. This may already be exceeding the amount of U.S. grain that can be diverted to fuel without driving world food prices to an unacceptably high level. And expanding cane-based ethanol in Brazil means putting more pressure on the remaining Amazonian rainforest. Shifting to plug-in hybrids powered with wind or solar generated electricity would avoid that. 84
As of mid-2007, growth in investment in ethanol and biodiesel was losing momentum as feedstock prices rose for both ethanol distilleries and biodiesel refineries and as soaring grain prices sounded alarm bells for food consumers everywhere. In Europe, with high goals for biodiesel use and low potential for expanding oilseed production, biodiesel refiners are turning to palm oil from Malaysia and Indonesia, where the clearing of rainforests for palm plantations is raising worldwide concern. 85
Work is now under way to develop efficient technologies to convert cellulosic materials such as switchgrass, woodchips, wheat straw, and corn stalks into ethanol. Switchgrass and hybrid poplars would produce relatively high ethanol yields on marginal lands, but it likely will be another decade before cellulosic ethanol can compete with corn-based ethanol. 86
An analysis by the American Solar Energy Society indicates that burning cellulosic crops to directly generate electricity is much more efficient than converting them to ethanol. The question is how much could plant materials contribute to the world’s energy supply. ASES estimates that the United States could generate 110 gigawatts of electricity from burning crops such as switchgrass and fast growing trees, roughly 10 times the current level. This projected growth assumes that the anticipated expansion in cellulosic crop production would be used primarily for electricity generation rather than ethanol production. We anticipate that the worldwide use of plant materials to generate electricity could contribute 200 gigawatts to generating capacity by 2020. 87
76. Kutscher, op. cit. note 61, p. 118; EIA, “Net Generation by Other Renewables,” at www.eia.gov/cneaf, updated 10 October 2007.
77. Swedish Energy Agency, Energy in Sweden 2005 (Eskilstuna, Sweden: November 2005), p. 37.
78. Population data from U.S. Bureau of the Census, State & County Quickfacts, electronic database, at quickfacts.census.gov, updated 31 August 2007; Anders Rydaker, “Biomass for Electricity & Heat Production,” presentation at Bioenergy North America 2007, Chicago, IL, 16 April 2007.
79. World Alliance for Decentralized Energy, Bagasse Cogeneration—Global Review and Potential (Washington, DC: June 2004), p. 32; sugar production from U.S. Department of Agriculture (USDA), Commodities and Products, electronic database, at www.fas .usda.gov/commodities, updated May 2007.
80. Waste to Energy Conference, “Power and Heat for Millions of Europeans,” press release, (Bremen, Germany: 20 April 2007).
81. Robin Pence, “AES AgriVerde: An AES-AgCert Joint Venture,” fact sheet (Arlington, VA: AES Corporation, May 2006).
82. Ray C. Anderson, presentation at Chicago Climate Exchange, Chicago, IL, 14 June 2006.
83. F.O. Licht, “World Fuel Ethanol Production,” World Ethanol and Biofuels Report, vol. 5, no. 17 (8 May 2007), p. 354; F.O. Licht, “World-Biodiesel Production (tonnes),” World Ethanol and Biofuels Report, vol. 5, no. 14 (23 March 2007), p. 291.
84. F.O. Licht, “World Fuel Ethanol Production,” op. cit. note 83; RFA, Ethanol Biorefinery Locations, at www.ethanolrfa.org, updated 28 September 2007.
85. Fiona Harvey et al., “Biofuels Growth Hit by Soaring Price of Grain,” Financial Times, 22 February 2007; Nigel Hunt, “Biofuel Bandwagon Slows as Feedstock Prices Surge,” Reuters, 5 October 2007; Bill Guerin, “European Blowback for Asian Biofuels,” Asia Times, 8 February 2007.
86. USDA, Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply (Washington, DC: April 2005).
87. Kutscher, op. cit. note 61, p. 127.
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