How much do cows offset wind energy savings?

So I saw this Tweet from Michael Eisen a couple of days ago:



This was in reference to a Slate article by Dan Gross about how Iowa is leading the US  in renewable energy, specifically wind-based. Having lived in Ames for over a year, I can tell you there is no shortage of wind in Iowa. There is no shortage of windmills either, but also there are quite a few cows. And cows are a serious source of methane, a greenhouse gas that is 25 times more potent than CO2.

So: does cow methane actually offset the greenhouse gas saved in Iowa by wind farms? Let’s check.

Coal, which is used in most Iowa power plants generates roughly 1kg CO2 for every 1kWh energy produced.

In 2015 Iowa generated 17,878,000,000 kWh from wind. That means 17,878,000,000 kg CO2 were not generated from coal. Since methane is a greenhouse gas 25 times more potent in trapping heat than CO2 that means that the equivalent of 715,120,000 kg of methane were not released to the atmosphere by using wind power.


Obligatory xkcd

And now, to our bovine friends, of which roughly 3.9 million inhabit our fair state of Iowa.

Interestingly, dairy cows and beef cows have different methane emissions. A dairy cow is twice as gassy as a beef cow with 100.7 kg/year of methane from the former, and 50.5 kg methane/year for the latter. Iowa has about 3,000,000 dairy cows, and 940,000 beef cows. 3 mil dairy cows in Iowa generate 332,100,000 kg methane, and 940,000 beef cows generate 47,470,000 kg methane for a grand total of 379,570,000 kg methane / year. Which is about half (53%) of the emissions saved by windmills (715,120,000).

So: while cows in Iowa produce quite a bit of methane, they are definitely not “destroying whatever gains” generated by wind energy.




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