How’s this for the next alternative-fuel du jour: biomethane. That’s right, methane gas derived from dairy manure offers a substitute for natural gas to power motor vehicles. The odorless gas is entirely renewable and environmentally friendly (apparently there is no smell). There are 8.5 million cows in the United States, producing enough manure to potentially power about a million cars, according to a group called Sustainable Conservation. Harnessing the methane from about 20 percent of California's cows could power all of the existing natural-gas-powered vehicles in the state, the group claims on its Web site. The group formed a coalition of energy, dairy and environmental groups to produce a study, "Biomethane from Dairy Waste: A Sourcebook for the Production and Use of Renewable Natural Gas in California." Researchers from Western Washington University recently demonstrated a technique for converting cow manure into horsepower, CBN News reports. The manure is harvested from the field and pumped into a holding tank. The manure “simmers” for about three weeks. Then workers siphon off the floating methane. With a few modifications, the fuel is ready to pump into a car modified to use natural gas. University researchers say it takes 15 to 20 cows a day to produce enough waste to power a car for about 300 miles. Yet the cost is 1/5th the price of regular gas, according to the CBN News report. The technologies for converting dairy manure to biomethane are already used at several landfills around the United States and elsewhere. Sweden, Sustainable Conservation reports, has 17 plants producing biomethane that power 7,000 cars and buses. In California, 12 methane digesters are now operating or under construction, which will generate about $1.6 million in electricity, or enough to power 2,000 homes.