Cows, long blamed for global warming, start giving back.

The poor cow has been much maligned by environmentalists. Their mere existence requires a massive burden on the land, and is often a cause of deforestation.

To top it off, their burps and farts release enormous quantities of methane, a potent greenhouse gas. A single cow releases 440 liters of methane per day.

But now a California utility, Pacific Gas & Electric, is working on project that will help cows give back to the grid.

PG&E will collect thousands of tons of cow manure from California cows, and convert it into biogas. Biogas is a renewable gas source, primarily composed of methane, that can be used interchangeably with natural gas to power the electric grid, or in compressed form power automobiles.

Certainly biogas has emissions problems. It still produces greenhouse gases, but like natural gas, it burns significantly cleaner than coal or oil. Given the number of cows in California, PG&E estimates that one day biogas could support 5% of their natural gas energy needs.

The current installation will provide enough electricity to power 50,000 electricity customers in California.