[marktangotango]

The fundamental reason is producing ethanol from corn requires quite a lot of energy; for cooking the mash and distilling the final product. If the cycle was entirely ethanol "all the way down" it could be carbon nuetral although using ethanol for production would detract from the "total efficiency". Invariably other fuels are used in production.

I went through the math a few years ago from the perspective of "micro power plants" for powering BTC mining. Coal is the winner from a cost perspective; but terribly dirty obviously. And capital intensive. Burning corn as fuel to a high efficiency boiler is actually more efficient than ethanol.