CLEANTECH: Milking Methane

By Published On: August 24, 2007

Pacific Gas & Electric and other utilities are signing anaerobic methane digestion deals to help meet their 20 percent renewables mandate. Just this week, for instance, the CPUC approved another biogas digester deal Pacific Gas & Electric signed (see story above). However, California’s dairy farms remain apathetic to the renewable energy from these digesters. Their apathy remains even though converting dairies methane-heavy manure to power could produce more than 200 MW, according to an environmental research organization. The main barriers to growing use of biogas digesters are said to be the lack of financial compensation for feeding biogas power into the grid, and the troubling side effects of biogas. According to Sustainable Conservation, an environmental think tank, the estimated 65 billion pounds of manure from California’s 2 million cows creates 18 billion cubic feet of methane a year. Methane is a greenhouse gas that is 23 times more potent than carbon dioxide. “There are about 15 dairy digesters in operation, and an additional half dozen under development,” said Allen Dusault, Sustainable Conservation’s director of sustainable agriculture. The number is relatively low considering four years ago 11 dairies were undergoing financing for biogas in response to the newly established net-metering law and California Energy Commission grants. Energy is produced from both biogas and bio-methane. However bio-methane, which is renewable natural gas containing up to 95 percent methane, has a much higher Btu content, since impurities, such as carbon dioxide and hydrodgen sulfide, are removed from the biogas with specialized scrubbers. However, some large dairies in the Central Valley are jumping on the bio-methane bandwagon. A handful of the larger farms in this area are partnering with greentech companies to run digesters on their land in exchange for augmenting their dairies natural gas supply to utilities. Digesters also avoid the release of cow dung methane into the atmosphere. In return qualifying dairies may receive greenhouse gas credits once the state’s global warming law, AB 32, is in force. The digesters provide other important benefits: they heavily reduce air and water pollution. Reducing air pollution could allow dairies to receive Renewable Energy Credits (RECs). The Central Valley, in particular, is one of the worst non–attainment areas of the country for air pollution. Advocates say that digesters improve water quality. But greentech firms serving the dairies must be permitted by the Central Valley Regional Water Quality Control Board before they can pump methane into California’s pipeline from their codigesters. Dairies can choose from a variety of digester technologies. The digester of choice for European farms and specialized green tech companies, is the efficient, thermophilic (heat-living bacteria) “co-digestion” system. They are also the least affordable for small-scale independent dairies. Bio-methane can be converted into megawatts but also less polluting transportation fuel. Liquefied methane can be used locally in heavy-duty vehicles like school buses and rubbish trucks. Farmers fear other hurdles as well. They may be subject to third party litigation, such as lawsuits from Sierra Club and The Center of Race, Poverty, and the Environment, who oppose installing biogesters at dairies with over 250 cows because of air and water quality impacts. California has a lot of catching up to do. Although recovering (renewable) manure methane may never become a dominant energy resource, it certainly will be a large part of the mix as California, and the nation, work toward attaining sustainable energy supplies. Editors’ note: For a more detailed version of the methane column, please see our sister publication E=MC2 – Energy Meets Climate Challenge. You can find it at

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