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Chapter 5. Stabilizing Climate: Shifting to Renewable Energy: Plant-Based Sources of Energy
As oil and natural gas reserves are being depleted, the world’s attention is also turning to plant-based energy sources. In addition to the energy crops discussed in Chapter 2, these include forest industry byproducts, sugar industry byproducts, urban waste, livestock waste, plantations of fast-growing trees, crop residues, and urban tree and yard wastes—all of which can be used for electrical generation, heating, or the production of automotive fuels.
The potential use of plant-based sources of energy is limited because even corn—the most efficient of the grain crops—can convert just 0.5 percent of solar energy into a usable form. In contrast, solar PV or solar thermal power plants convert roughly 15 percent of sunlight into a usable form, namely electricity. In a land–scarce world, energy crops cannot compete with solar electricity, much less with the far more land-efficient wind power. 83
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 nearly 11,000 megawatts in U.S. plant-based electrical generation comes primarily from burning forest waste. 84
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 2007 oil had been largely replaced by wood chips and urban waste. 85
In the United States, St. Paul, Minnesota—a city of 275,000 people—began to develop district heating more than 20 years ago. It built a combined heat and power plant to use tree waste from the city’s parks, industrial wood waste, and wood from other sources. The 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. 86
Oglethorpe Power, a large group of utilities in the state of Georgia, has announced plans to build up to three 100-megawatt biomass-fueled power plants. The principal feedstocks will be wood chips, sawmill wood waste, forest harvest residue, and, when available, pecan hulls and peanut shells. 87
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 their fermentation process and generate electricity that they could sell to the local utility. This system, now well established, is spreading to sugar mills in other countries that produce the remaining four fifths of the world’s sugar harvest. 88
Within cities, garbage is also burned to produce heat and power after, it is hoped, any recyclable materials have been removed. In Europe, waste-to-energy plants supply 20 million consumers with heat. France, with 128 plants, and Germany, with 67 plants, 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. It would, however, be preferable to work toward a zero-garbage economy where the energy invested in the paper, cardboard, plastic, and other combustible materials could largely be recovered by recycling. Burning garbage is not a smart way to deal with the waste problem. 89
Until we get zero waste, however, the methane (natural gas) produced in existing landfills as organic materials in buried garbage decompose can also be tapped to produce industrial process heat or to generate electricity in combined heat and power plants. The 35-megawatt landfill-gas power plant planned by Puget Sound Energy and slated to draw methane from Seattle’s landfill will join more than 100 other such power plants in operation in the United States. 90
Near Atlanta, Interface—the world’s largest manufacturer of industrial carpet—convinced the city to invest $3 million in capturing methane from the municipal landfill and to 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 while reducing operating costs for Interface. 91
As discussed in Chapter 2, crops are also used to produce automotive fuels, including both ethanol and biodiesel. In 2009 the world was on track to produce 19 billion gallons of fuel ethanol and nearly 4 billion gallons of biodiesel. Half of the ethanol will come from the United States, a third from Brazil, and the remainder from a dozen or so other countries, led by China and Canada. Germany and France are each responsible for 15 percent of the world’s biodiesel output; the other major producers are the United States, Brazil, and Italy. 92
Once widely heralded as the alternative to oil, crop-based fuels have come under closer scrutiny in recent years, raising serious doubts about their feasibility. In the United States, which surged ahead of Brazil in ethanol production in 2005, the near doubling of output during 2007 and 2008 helped to drive world food prices to all-time highs. In Europe, with its high goals for biodiesel use and low potential for expanding oilseed production, biodiesel refiners are turning to palm oil from Malaysia and Indonesia, driving the clearing of rainforests for palm plantations. 93
In a world that no longer has excess cropland capacity, every acre planted in corn for ethanol means another acre must be cleared somewhere for crop production. An early 2008 study led by Tim Searchinger of Princeton University that was published in Science used a global agricultural model to show that when including the land clearing in the tropics, expanding U.S. biofuel production increased annual greenhouse gas emissions dramatically instead of reducing them, as more narrowly based studies claimed. 94
Another study published in Science, this one by a team from the University of Minnesota, reached a similar conclusion. Focusing on the carbon emissions associated with tropical deforestation, it showed that converting rainforests or grasslands to corn, soybean, or palm oil biofuel production led to a carbon emissions increase—a “biofuel carbon debt”—that was at least 37 times greater than the annual reduction in greenhouse gases resulting from the shift from fossil fuels to biofuels. 95
The case for crop-based biofuels was further undermined when a team led by Paul Crutzen, a Nobel Prize–winning chemist at the Max Planck Institute for Chemistry in Germany, concluded that emissions of nitrous oxide, a potent greenhouse gas, from the synthetic nitrogen fertilizer used to grow crops such as corn and rapeseed for biofuel production can negate any net reductions of CO2 emissions from replacing fossil fuels with biofuels, thus making biofuels a threat to climate stability. Although the U.S. ethanol industry rejected these findings, the results were confirmed in a 2009 report from the International Council for Science, a worldwide federation of scientific associations. 96
The more research is done on liquid biofuels, the less attractive they become. Fuel ethanol production today relies almost entirely on sugar and starch feedstocks, but work is now under way to develop efficient technologies to convert cellulosic materials into ethanol. Several studies indicate that switchgrass and hybrid poplars could produce relatively high ethanol yields on marginal lands, but there is no low-cost technology for converting cellulose into ethanol available today or in immediate prospect. 97
A third report published in Science indicates that burning cellulosic crops directly to generate electricity to power electric cars yields 81 percent more transport miles than converting the crops into liquid fuel. The question is how much could plant materials contribute to the world’s energy supply. Based on a study from the U.S. Departments of Energy and Agriculture, we estimate that using forest and urban wood waste, as well as some perennial crops such as switchgrass and fast-growing trees on nonagricultural land, the United States could develop more than 40 gigawatts of electrical generating capacity by 2020, roughly four times the current level. For Plan B, we estimate that the worldwide use of plant materials to generate electricity could contribute 200 gigawatts of capacity by 2020. 98
83. Stephen R. Gliessman, Agroecology: The Ecology of Sustainable Food Systems, 2nd ed. (Boca Raton, FL: CRC Press, 2006), p. 256; Pew Center on Global Climate Change, “Climate TechBook: Solar Power,” fact sheet (Arlington, VA: May 2009); Richter, Teske, and Short, op. cit. note 52, pp. 18–19.
84. Ralph P. Overend and Anelia Milbrandt, “Potential Carbon Emissions Reductions from Biomass by 2030,” in Kutscher, op. cit. note 51, pp. 112–30; DOE, op. cit. note 51, p. 24.
85. Swedish Energy Agency, Energy in Sweden 2008 (Eskilstuna, Sweden: December 2008), pp. 96, 111.
86. Population data from Census Bureau, op. cit. note 1; Anders Rydaker, “Biomass for Electricity & Heat Production,” presentation at Bioenergy North America 2007, Chicago, IL, 16 April 2007.
87. Oglethorpe Power Corporation, “Oglethorpe Power Announces Plans to Build Biomass Electric Generating Facilities,” press release (Tucker, GA: 18 September 2008).
88. 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), Production, Supply and Distribution, electronic database, at www.fas.usda.gov/psdonline, updated 9 April 2009.
89. Waste to Energy Conference, “Power and Heat for Millions of Europeans,” press release (Bremen, Germany: 20 April 2007); Confederation of European Waste-to-Energy Plants, “2008 Country Reports on Waste Management,” at www.cewep.eu, viewed 23 July 2009; Jeffrey Morris, “Comparative LCAs for Curbside Recycling Versus Either Landfilling or Incineration with Energy Recovery,” International Journal of Life Cycle Assessment, vol. 10, no. 4 (July 2005), pp. 273–84.
90. Puget Sound Energy, “King County, PSE, and Bio Energy-Washington Teaming Up to Generate Green Energy from Landfill Gas,” press release (Seattle, WA: 6 April 2009).
91. Ray C. Anderson, presentation at Chicago Climate Exchange, Chicago, IL, 14 June 2006.
92. F.O. Licht, “World Fuel Ethanol Production,” World Ethanol and Biofuels Report, vol. 7, no. 18 (26 May 2009), p. 365; F.O. Licht, “Biodiesel: World Production, by Country,” World Ethanol and Biofuels Report, vol. 7, no. 14 (26 March 2009), p. 288.
93. F.O. Licht, “World Fuel Ethanol Production,” op. cit. note 92, p. 365; Bill Guerin, “European Blowback for Asian Biofuels,” Asia Times, 8 February 2007.
94. Timothy Searchinger et al., “Use of U.S. Croplands for Biofuels Increases Greenhouse Gases through Emissions from Land-Use Change,” Science, vol. 319 (29 February 2008), pp. 1,238–40.
95. Joseph Fargione et al., “Land Clearing and the Biofuel Carbon Debt,” Science, vol. 319 (29 February 2008), pp. 1,235–38.
96. “Biofools,” The Economist, 11 April 2009; P. J. Crutzen et al., “N2O Release from Agro-biofuel Production Negates Global Warming Reduction by Replacing Fossil Fuels,” Atmospheric Chemistry and Physics, vol. 8 (29 January 2008), pp. 389–95; industry reaction from Lauren Etter, “Ethanol Craze Cools As Doubts Multiply,” Wall Street Journal, 28 November 2007; R. W. Howarth and Stefan Bringezu, eds., Biofuels: Environmental Consequences and Interactions with Changing Land Use, Proceedings of the Scientific Committee on Problems of the Environment (SCOPE) International Biofuels Project Rapid Assessment, 22–25 September 2008 (Ithaca, NY: Cornell University, 2009), pp. 1–13.
97. DOE, EERE, “Starch- and Sugar-Based Ethanol Feedstocks,” at www.afdc.energy.gov/afdc/ethanol/feedstocks_starch_sugar.html, updated 4 February 2009; DOE and USDA, Biomass as Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply (Washington, DC: April 2005); Jason Hill et al., “Environmental, Economic, and Energetic Costs and Benefits of Biodiesel and Ethanol Biofuels,” Proceedings of the National Academy of Sciences, vol. 103, no. 30 (25 July 2006), pp. 11,206–10; M. R. Schmer et al., “Net Energy of Cellulosic Ethanol from Switchgrass,” Proceedings of the National Academy of Sciences, vol. 105, no. 2 (15 January 2008), pp. 464–69; Purdue University, Department of Agricultural Communication, “Fast-Growing Trees Could Take Root as Future Energy Source,” press release (West Lafayette, IN: 23 August 2006).
98. J. E. Campbell, D. B. Lobell, and C. B. Field, “Greater Transportation Energy and GHG Offsets from Bioelectricity than Ethanol,” Science, vol. 324 (22 May 2009), pp. 1,055–57; DOE and USDA, op. cit. note 97, pp. i–ii.
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