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Corn Ethanol
The Net Energy Value of Ethanol
Making ethanol uses up non-corn (ordinary) energy. If it uses more more than is in the ethanol, the "net energy balance" of ethanol is negative. But it would still save gasoline because a lot of the energy used to make ethanol comes from coal. In effect we would be turning coal into gasoline. But burning coal makes more CO2 than burning gasoline, so this would increase greenhouse gas emissions.
Contrary to ethanol critics like Pimentel and Patzek, the best studies indicate ethanol's net energy balance is positiveóbut not by a lot. Most studies find it takes 74% to 80% as much non-corn energy to make ethanol as is in the ethanol made. The diagrams below assumes 75%, which is optimistic compared with the latest report by the National Academy of Sciences. It also doesn't count nuclear or hydro inputs, only fossil energy inputs, and it overstates, by a little, the energy needed to make gasoline.
Just remember, a positive net energy balance does not tell us that greenhouse gases are reduced, how much energy imports are reduced, or what all this costs.
zFact:Using 3 gallons of ethanol
saves as much fossil energy as in
1 gallon of gasoline.

Using ethanol save fossil two ways: 
(1) One quarter of the energy in ethanol comes from corn, nuclear and hydro (mostly corn).
(2) Replacing a gallon of gasoline replaces about one quarter more energy than in the gallon, becasue fossil used to make gasoline.
The energy in a gallon of gasoline is called 1 GGE of energy.
Making and using 4 GGE of ethanol requires 3 GGE of fossil fuel, but saves the (almost) 5 GGEs of fossil fuel needed for the 4 gallons of gasoline replaced.
This means, 4 GGE of ethanol saves 2 GGE of fossil fuel.
But ethanol has only 2/3 the energy of gasoline, so 4 GGEs of ethanol is 6 gallons of ethanol. It takes 6 gallons of ethanol to save 2 GGE, the energy in 2 gallons of gasoline.
  Above diagram based on net energy values from Argonne National Lab Study.
    1 GGE of ethanol requires 0.74 (rounded to 0.75) GGE of fossil input energy.
    1 GGE of gasoline require 1.23 (rounded to 1.25) GGE of fossil input energy.
Also on number of galons of ethanol with 1 GGE of energy = 1.53 (rounded to 1.5).

http://zfacts.com/p/83.html | 01/18/12 07:17 GMT
Modified: Thu, 19 Apr 2007 22:55:34 GMT
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