Doing the math on ethanol as biofuel

June 4, 2013

At the start of a mostly pleasant volunteer experience at Marra Farm this past Saturday, the volunteer coordinator offered a rather politicized summary of why eco-friendly community farms like Marra are important.

One of the things she was clearly against was growing corn to produce ethanol for biofuel. She said that if a 4-acre farm like Marra was used entirely for corn production, the resulting ethanol would only be enough “to fill up the tank of one SUV.”

This sounded implausible to me, so I did some quick Internet research when I got home.

According to ethanolrfa.org (not the best possible source, but a convenient one), an acre of land can produce about 150 bushels of corn per year, and it takes about 0.36 bushels to produce a gallon of ethanol.

Therefore the ethanol output of 4 acres would be
(4 acres)*(150 bushels/acre)*(1 gallon ethanol/0.36 bushels) = 1667 gallons of ethanol.

That amount of ethanol may be enough to power one SUV for a year. Maybe that’s what the volunteer coordinator meant.


  1. Greg,
    Unless you plan to plant and harvest (and spray etc) those entire 4 acres by hand, your gonna need a tractor. Granted tractors run on diesel, but it takes some fuel to do that. It also takes some energy to convert the corn.

    Everything i have read or calculated indicated that when you take all of the overhead into consideration, 1700 gallons of ethanol from 4 acres is a money/fuel loser, even with some of the subsidies.

    OTOH, i think you can do better with soybeans going to diesel.


    • I agree completely, Tim. Even without including harvesting costs, sacrificing 4 acres to fuel a single vehicle seems like a very bad idea. So I ultimately agreed with the volunteer coordinator’s general point even though I didn’t love the way she presented it.

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