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Switching to switchgrass. (Recycling).

Biomass fuels offer a tantalizing sidestep around global warming. When burned, they produce the greenhouse gas carbon dioxide, but their growth takes up a similar amount of the gas, thus producing essentially no net increase in atmospheric carbon. Almost all biomass fuel is waste residue from forestry, agriculture, or industry, and biomass fuels can also be grown as crops. Several recent demonstration projects have tested the use of switchgrass, a perennial prairie grass native to North America, in electric generating stations.

Biomass fuels are second only to hydropower as a fuel for mass utility-administered consumer use. In May 2001, for example, biomass generated about 1.8% of the total 307 trillion kilowatt-hours produced that month, according to U.S. electric power industry summary statistics published by the federal Department of Energy (DOE).

In a test cosponsored in December 2000 by the DOE, the Centerville, Iowa-based nonprofit Chariton Valley Resource Conservation and Development, and the utility holding company Alliant Energy, switchgrass was burned at a generator in Iowa. Thirteen hundred tons of switchgrass was harvested with a hay baler, chopped into short pieces, and burned with coal in a 725-megawatt boiler. The generator ran normally, with switchgrass supplying up to 13 megawatts of electricity. "You could not tell you were running switchgrass," says Richard Bain, the biopower group manager in the National Bioenergy Center at the National Renewable Energy Laboratory in Golden, Colorado. Recently Southern Company, a large electric utility in the southeastern United States, successfully completed a similar test in Gadsden, Alabama, with switchgrass contributing 7-10% of the energy produced during the test period.

Douglas Boylan, a research engineer with Southern, says switchgrass and similar biomass crops have several environmental advantages over coal, which, according to the DOE, fuels about 40% of U.S. utility electric generation. The emissions, he says, are very low in sulfur dioxide and mercury, two major pollutants associated with coal.

One acre of a switchgrass plot can grow the energy equivalent of about 2-6 tons of foal per year, says Bain, depending on fertilization and other variables. Boylan says one large bale of switchgrass produces enough power to serve a typical house's electricity needs for a month.

Growing switchgrass is also a sustainable practice in itself. Biomass crops typically produce 15-25 times as much electric energy as the heat energy in the fossil fuels needed to grow, process, and transport them, Bain says. Research by Resource Efficient Agricultural Production (REAP), a Canadian nonprofit group that studies sustainable fuels and agricultural practices, indicates that switchgrass requires only modest amounts of fertilizer for optimal growth. Switchgrass grows year after year in one location without recurrent soil preparation, greatly reducing soil erosion and runoff associated with annual tillage that might be needed for other biomass crops. And as a wildlife habitat, switchgrass is better than row crops, says Roger Samson, director of international projects for REAP.

Some say switchgrass's true strength lies in being used directly to warm buildings or to replace wood as a cooking fuel. Samson says burning switchgrass in coal-fired generators produces about 32% efficiency, but when switchgrass is pressed into pellets and burned in specially designed space-heating stoves, the efficiency reaches 85%.

About the only bad mark on the switchgrass scorecard is economics. Although the exact price is not yet clear, in tests to date switchgrass appears to cost more than coal to produce electricity. "I think using dedicated crops like switchgrass is going to be more expensive than coal," Bain says, "but it will depend on the specific system." Samson agrees that switchgrass costs more than coal to produce electricity, but adds, "Switchgrass pellets provide heat for about thirty percent less than heating oil."
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Author:Tenenbaum, David J.
Publication:Environmental Health Perspectives
Date:Jan 1, 2002
Words:611
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