Methane will be used to generate electricity. Cows reliably produce two things. One is milk. The other soon will become a source of your electric power.

Cattle manure meets the New Energy Economy next year when a New York firm plans to build the nation's largest plant for converting livestock waste into fuel — methane gas — for generating electricity.

Xcel Energy has agreed to buy the gas for its Fort St. Vrain power plant near Platte ville.

The $30 million "biogas" facility will be built at a site not yet chosen in Weld County.

The concept is not new. Several livestock feeding and dairy operations in Colorado have methane-collection systems fueling small, on-site power generators.

But the plant being developed by Tarrytown, N.Y.-based Environmental Power Corp. will be much larger than any similar system in Colorado.

The facility's 12 silo-shaped anaerobic digesters will produce enough methane to power 17,000 Colorado homes, the company said.

Although the methane will replace just 3 percent of Fort St. Vrain's regular natural-gas consumption, it will help toward a mandate that Colorado utilities produce 20 percent of their power from renewable sources by 2020.

"There's great potential for using biogas," said Stacey Simms, a biofuels expert with the Colorado Governor's Energy Office. "Anaerobic digestion makes a lot of sense and can be an important source of renewable energy. It's a good fit for utilities."

The technology is simple: Manure and other organic waste emit methane as they decompose. The biogas facility will collect the gas, clean it and ship it to Fort St. Vrain via pipeline.

At the power plant, natural gas — whether from conventional underground sources or manure-derived methane — is ignited. The resulting hot gas spins jet-engine-like turbines that produce electricity.

Fort St. Vrain was built in the 1970s as a nuclear power plant, but it was decommissioned after a series of technical problems and later converted to gas power.

Microgy, a subsidiary of Environmental Power, has patented a process that it says is more efficient because it can use a variety of organic wastes. In addition to manure, it can use food-processing byproducts and wastes from carcass-rendering plants.

Microgy has some small-scale digesters in Wisconsin and a larger facility in central Texas from which the methane it produces is sold to Pacific Gas & Electric in California.

Xcel's deal calls for the utility to pay Microgy a premium over market prices for conventional natural gas.

For related articles, link to The Denver Post. Steve Raabe: 303-954-1948 or sraabe@denverpost.com