A group of California Central Valley dairies have announced their participation in the nation’s largest effort to convert methane from cow manure into biogas. The potential for methane to warm the atmosphere is 30 times greater than that of carbon dioxide, and California cattle account for half of the state’s methane emissions, according to its Air Resources Board.

The biogas project, a joint effort between Calgren Dairy Fuels and Southern California Gas, is expected to yield 3 million to 4 million gallons of renewable natural gas (RNG) a year. The RNG processed by Calgren is injected into the utility’s system.

“This facility alone will eventually capture methane produced from the manure of more than 75,000 cows, preventing about 130,000 tons of greenhouse gas emissions from entering the atmosphere each year, the equivalent of taking more than 25,000 passenger cars off the road annually,” said Lyle Schlyer, president of Calgren Renewable Fuels.

The expansion is the latest response to a 2016 law passed in California, the nation’s largest dairy producer, calling for a 30 percent reduction in methane emissions from dairies by 2030. The mandate was supported by funding to support the creation of methane digesters on dairy farms.

A “digester” is a manure pond covered by a flexible membrane. The membrane keeps oxygen out, with the result that bacteria in the manure “think they’re still in a cow’s stomach,” says Daryl Maas of Maas Energy, a digester developer and operations company that is working with farmers in in the region.

“They eat the remaining calories and they emit methane gas,” he adds. The gas is captured and then processed into RNG, a transformation that is colloquially referred to as “poo to power.”

This transition can also involve “poo to profit,” as farmers receive income for the gas they provide for processing. These payments can be in the range of six figures, according to Maas.

“Over the last five years, renewable natural gas use in the transportation sector has grown by almost 600 percent,” said Sharon Tomkins, SoCalGas vice president and chief environmental officer. “We’re looking to build on that success by delivering more renewable energy options to our customers, including renewable natural gas produced at farms, hydrogen made from surplus solar energy, and advanced fuel cell systems that can provide energy in extreme weather events.”

Carl Smith is a contributing writer to Governing.