Undercurrents: beneath the obvious

December 6, 2006

Ethanol Not So Green After All?

Filed under: Ethanol — nemo @ 9:26 pm

Following on from my previous post on Ethanol here.

Turning plants such as corn, soybeans and sunflowers into fuel uses much more energy than the resulting ethanol generates, according to a  Cornell University and University of California-Berkeley study. David Pimentel and Tad W. Patzek conducted a detailed analysis of the energy input-yield ratios of producing ethanol from corn, switch grass and wood biomass as well as for producing biodiesel from soybean and sunflower plants.

In terms of energy output compared with energy input for ethanol production, the study found that:

  • corn requires 29 percent more fossil energy than the fuel produced;
  • soybean plants requires 27 percent more fossil energy than the fuel produced, and
  • sunflower plants requires 118 percent more fossil energy than the fuel produced.

"The United State desperately needs a liquid fuel replacement for oil in the near future," says Pimentel, "but producing ethanol or biodiesel from plant biomass is going down the wrong road, because you use more energy to produce these fuels than you get out from the combustion of these products."

Currently the U.S. is producing 4.5 billion gallons of ethanol (DOE) without charging for the oil and natural gas inputs. This is using 18% of all U.S. corn and represents only 1% of U.S. petroleum use. If 100% of U.S. corn were used, it would provide only 6% of current U.S. petroleum use.

There’s a final point to be raised about ethanol: It contains only about two-thirds as much energy as gasoline. Thus, when it gets blended with regular gasoline, it lowers the heat content of the fuel. So, while a gallon of ethanol-blended gas may cost the same as regular gasoline, it won’t take you as far.

Source: Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower (pdf)

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