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How Many Cowpower is That?
Zlorfik writes: " Accoring to a a Des Moines Register story, a new facility in Iowa can generate enough renewable energy from 700 cows to power 1,000 100-watt bulbs." This sounds like a good reason to switch to a slightly more efficient lighting system.
I think the power supply would be continuous, barring any brownouts or other power interruptions. It would be pretty inefficient if they had to wait for more manure every time they wanted more power. As for why the light bulbs, that's probably since for most people, it's easier to picture 1000 100-watt light bulbs than actually figure out what 100kW is useful for.
CH4 (methane) + 2 02 (oxygen) -> 2 H2O (water) + CO2
But, considering that the greenhouse effect of methane is much larger than that of CO2, this is not a problem.
On a related note, many gasses have an effect on the greenhouse phenomenon. CO2 is the most famous one because it's the one that varies the most, and the one that (according to most scientists) has an increasing concentration due to human activities.
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As long as the cows aren't eating coal, petroleum or natural gas from a well, the carbon in their manure came from plant sources. Plants get thier carbon from the air. It's a zero-sum game. The big idea behind the problem with CO2 release is all the people releasing the carbon that was locked away deep underground as limestone (to make concrete) or fossil fuels.
Additionally, methane is much less stable than CO2 in the atmosphere. I forget the pricise figures, but I think the residence time for your average methane molecule is 1-2 years. Depending on your ocean uptake numbers, CO2 residence is in the 100's of years.