Ethanol from Corn: Net Energy Gain?

-So what if ethanol from corn has a positive energy balance?

Every time I fill up my car, I see a sign reminding me the “gas” is a mixture of ethanol and real gasoline. Newspapers and magazines contain articles about the debate on whether more energy goes into the production of ethanol from corn than we get out of it when we use it in our cars.  And I know there are a range of views on whether the taxpayers should help foot the bill for ethanol production.

I decided to look into the question of how much energy goes into the production of ethanol from corn versus how much energy is contained in the final product, the so-called energy balance issue.   My naive belief was that if it takes more energy to produce ethanol than you get out of it, then using the taxpayers’ money to support the program was a bad idea.  I learned the energy balance issue is a red herring. The ethanol energy balance issue is not significant in the larger context of our energy needs.  Converting corn (or other plants) into ethanol can be a partial alternative to drilling for oil, but ethanol is unlikely to play a major role in meeting our long-term energy needs.

To determine the ethanol energy balance, one must account for all the fossil energy used in activities that go into growing corn and turning it into fuel for our cars.  These include the production of fertilizer, farming, transporting raw and finished materials, operating the processing plant that turns corn into ethanol,  etc. The ingoing energy comes from coal and natural gas to produce heat and electricity and from petroleum to fuel the transport vehicles.  A Department of Energy publication reports a net gain of about 15% in energy for the production of ethanol from corn. So the energy balance is positive.

(Michael Wang provides a useful discussion of the assumptions and models used to calculate the energy required to produce ethanol.  Note that “free” solar energy that ends up in the corn is not included in the energy balance.)

However, ethanol can play only a limited role in meeting our transportation energy needs. The engines in today’s cars can burn gas that is about 10% ethanol.  Adding more ethanol will damage the engine. Modifying cars to use higher concentrations of ethanol would be a major undertaking.

Even if cars are modified to use higher concentrations of ethanol, there are significant challenges in producing the amounts of ethanol required for it to be a major source of energy for transportation. These challenges include a limited amount of land that can be  farmed and the need to use that land to grow food.

David MacKay thinks biofuels are “scarcely worth talking about” in the context of Britian’s energy needs. I think MacKay’s observation applies as well to the US.  Ethanol will not make a significant contribution to our energy needs.


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