Posted by: carlbrannen | April 25, 2008

Pimental and Corn Ethanol Fuel

Back in 2001, David Pimental, a professor of entomology at Cornell, published a paper which concluded, among many other wrong things, that it takes 131,000 BTUs of energy to make a gallon of ethanol, which has energy content of only 77,000 BTUs.

You would think that pronouncements by entomology professors on the subject of the manufacture of ethanol would be ignored but due to the surprising conclusion of the paper, it received a great deal of press and it continues to receive press, being quoted by right wing commentators who wish to eliminate government subsidies , and by left wing commentators who wish to see industry reduced and “factory farming” eliminated.

The faulty calculations of Pimental’s silly paper have been repeatedly blasted in the literature, and less often in the press, but the average person doesn’t have the time to learn enough engineering, physics, chemistry, biology and economics to understand these papers. Rather, people tend to believe the tales they are told based on their estimate of the sanity of the person who does the telling. To give the reader a better idea of who Pimental is, I’ve collected a few of his other papers here. He’s a deep ecologist, a modern Malthusian. Enjoy:

Contamination of water, air and soil leads to 40 percent of the planet’s death toll, according to a study conducted by Prof. David Pimentel, ecology and evolutionary Biology.

Food, Land, Population and the U.S. Economy (1994):

Reducing the U.S. population to 200 million, while reducing the consumption of energy and other resources by one-half, is a first difficult step. Then, with the effective development of solar energy technologies, a quality of life similar to that of our European friends would be possible.

Also see Ecology of Increasing Disease

Oddly enough, Pimental is in favor of genetically modified organisms: Genetically Modified Crops and the Agroecosystem: …



  1. Hi Carl

    I have seen the conclusion of Pimental’s paper printed so many times that it proves Barnum’s Law.

    Any idea on the true BTU cost of a gallon of ethanol? I have seen around 50,000 BTU’s used or 25% net gain as well in many publications.


  2. Paul,

    Different methods of storing energy have different economic values so counting BTUs is an amusement for academics but not of any real use.

    Ethanol is a very valuable fuel because it can be used in a standard gasoline internal combustion machine. The same cannot be said of natural gas nor electricity, which are the two major energy inputs of an ethanol plant, nor can it even be said of diesel used on farms, or the electricity used to pump water for irrigation.

    To see if there is economic value in converting corn to ethanol is easy. Just compare their prices.

  3. that seems like an ignorant response: ‘just compare their prices’. this is why people wonder about subsidies. if you need alot of oil for fuel and fertilizer and transportation to produce the corn, which is paid for by subsidies, then ethanol may not pay for itself unless these hidden costs are subsidized.

    the padzyk (sic) (stanford)/pimental ‘thermodynamic’ fuel cycle articles are not convincing (since they are mostly cluttered with irrelevant discussions (which look technical) but they raise these points; science magazine had a better review which concluded the efficiency was about 1.3 gallons ethanol for 1 gallon oil (or maybe other fuels).

    one can also get into global warming.

  4. Mark, there are other articles in competition with Pimental that say the opposite. For example, fertilizer is a tiny percentage of the farm budget how can it possibly be the target of significant subsidies? What are these fertilizer subsidies? And how much do the fertilizer companies pay in taxes? Shouldn’t that be subtracted from the subsidy?

    And as you hinted, counting things up in BTUs is silly because you can’t put corn or natural gas into your car.

    For our plant, Pimental’s calculations do not apply in many ways. First, our plant is being built from used industrial equipment. Therefore it’s cost, both in dollars and to the environment, is much lower than a plant built from all new steel. Second, we are permitted to run on barley as well as corn. Barley is a dry land crop that can be grown on idle farm land all over Washington State without irrigation. So the costs of fertilizer and water do not necessarily enter into the cost of the feedstock of our plant.

    Perhaps the best argument against the idea that the only way that ethanol pays its way is through US agricultural subsidies is to note that corn is turned into ethanol in many of the other countries that produce significant amounts of corn: Canada, China, South Africa, and France. Are US corn subsidies being copied all over the world? And in Europe, various other grains are turned into ethanol for fuel, barley, wheat, and rye as well as sugar beets (which we are considering, but to use it, we’d have to get a modification of our air and water ecology permits).

    No. It’s very simple, really. As corn prices stay relatively low (i.e. under $6 per bushel), and oil prices are relatively high (i.e. over $100 per barrel) turning corn into fuel is quite profitable.

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