Commenter Calvin left the following on Tuesday's biogas post:
Great thinking, I love this, just wondering what impact methane gas has on global warming? Is this cheap and sustainable? or just cheap, like coal? thanks, love your work!
My response to Calvin was getting lengthy, and I thought it might have more impact if I posted it more widely. Besides, I'm a biogas junkie, so I love any opportunity I get to read, learn and write about biogas.
|Biogas stove in Uganda.|
Great question, Calvin. Here's the short answer: it's cheap AND sustainable. Here's the more complicated answer:
First, biogas comes from waste, which is obviously quite renewable, as opposed to fossil fuels. Second, the waste (let's just talk manure from livestock to keep things simple) will emit methane gas no matter what. So, a cow poops in a field, and when that manure breaks down naturally, methane gas is emitted into the atmosphere. (On a small farm like those of our project participants, this isn't the significant Problem it is like the methane-emitting manure produced on feedlots in the United States and elsewhere, but that's another story.)
Okay, so biogas works thorough anaerobic digestion, which more efficiently converts the manure into a gas that's made up of about 60 percent methane and 40 percent carbon dioxide. Burning this biogas reduces the greenhouse gas impact by more than 20 times what the waste would produce naturally. So, biogas is great because it's a) reducing the impact the waste would have anyway and b) displacing the burning of fossil fuels, which have a larger greenhouse gas impact. Further, biogas is considered part of the natural carbon cycle, since the carbon that is emitted when biogas is burned originated from carbon fixed by plants.