On Tuesday, California energy company PG&E started generating energy from a rather unusual source: cow manure. Yes, cow poop emits methane as it decomposes. And while usually that's a bad thing, with methane being a potent greenhouse gas and all, it can be captured and turned into a renewable source of energy.
So that's just what PG&E is doing, using manure to power up to 1,200 homes in California. It's all part of new regulations in the state that are to require utility companies to have 20% of their energy coming from renewable sources by 2010. With a figure that high, they need to look outside the standard solar and wind sources.
So how exactly do you turn cow crap into energy? How's a 10-metre-deep pit full of the stuff sound? Get ready to appreciate your desk job a little bit more:
To tap the renewable gas from cow manure, the Vintage Dairy farm first flushes manure into a large, octagonal pit, where it becomes about 99 percent water. It is then pumped into a covered lagoon, first passing through a screen that filters out large solids that eventually become the cows' bedding.
The covered lagoon, or "digester," is the size of nearly five football fields and about 33 feet deep. It is lined with plastic to protect the ground water and the cover, made of high density polyethylene, is held down at the edges by concrete. The digester's cover was sunken into the lagoon on Tuesday, but officials said it would be taut and raised in a few days as the gas collects underneath it.
Weights on top of the digester channel the gas to the small facility where it is "scrubbed" of hydrogen sulfide and carbon dioxide. The end product is "close to 99 percent pure methane" according to BioEnergy Chief Operating Officer Thomas Hintz.