2% National Coutput -or- 10,000 Cows per MW

A commenter on my recent pro-transmission article questioned some statements of mine about the availability of renewable electricity from cow manure.  I had stated that 

  1. It was most likely baseload.
  2. There was not much of it in many states.

The first observation comes from the fact that the digester is sized so that
it runs as much as possible to produce the best economics.  Manure also
breaks down over time, and so is likely to yield more electricity if used as
quickly as possible after it’s produced.

Total Cow Output (Coutput?)

I thought it would be interesting to run some numbers and see how much
electricity might be available from cow manure.  First I had to come up
with some numbers for kWh/cowyear.  I found an example of a 50 kW engine running 14h/day on the produce of 300 cows.

That’s 850 kWh/cowyear, or about 100 W/cow, or 10,000 cows/MW.  A single cow produces enough manure to run one incandescent light bulb (or four CFLs) year round.

The US has about 100 million cattle, capable of producing 10 GW of electricity (if all the manure was gathered and processed in anaerobic digesters,) or 85 million MWh/year.  Total US Electricity production in 2007 was 4,208 million MWh, so 100% conversion of cow power into electricity could supply 2% of total US electricity.

100% conversion is a rather heroic assumption, especially for pastured cows, but I’m not including other types of livestock (pigs, chickens, etc.) so 2% of electricity seems like a reasonable potential estimate for total anaerobic digestion of manure. 

2% is actually a higher number than I would have expected, although that potential for electricity generation is unlikely to be reached, since much might be converted to liquid fuels for transport.

1 Comment

  1. Matt Lemke said

    Interesting, just reviewing a couple of Articles on some websites,

    Wisconsin has 21 digesters on dairy farms capable of producing over 75 million kilowatts of electricity per year.

    http://www.wisgov.state.wi.us/docview.asp?docid=13459 (Page 7)

    ANother article notes ~1200 kwhr/year per cow for Biogas. This was in 2004.

    This article notes some interesting facts about the various digestors in Wisconsin. It seems like the power potential is pretty impressive for large farms. (2000 cows)


    Not sure what a good number is for per cow potential, but the latest numbers seem to be showing some impressive gains. Would other animal waste off better potential? Not sure. Seems like the US has a lot of options though. Dairy farmers who install the digesters directly on their property, allows the waste to be collected immediately, for prime quality. So perhaps the viability is better the closer to the source?

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