Ethanol as a fuel is hard to nail down where it really fits - when the US started big production, it was for cleaner air in California (E10 burns hotter than just petrol, and therefore cleaner, with greatly reduced particle emissions, responsible for "smog"), and as another innovative way to subsidise farmers. The energy "cost" of 1 litre of ethanol, adding up agricultural production, fertilizer, and processing energy costs, was about 1.2 litres of oil...hardly inspiring.
Thanks to using filters to remove water instead of distillation after heating, and other processing innovations, ethanol cost is now at least positive, about .8 litres of oil per litre of ethanol produced. But that is not going to save the world, all it does is use oil to slightly extend oil supply with a renewable component. Added to that is the heavy reliance on cheap urea from oil to produce high corn yields - so the ethanol produced is not the replacement fuel it is touted to be.
It can be produced at a subsistence level to enable some transport, as happened in WW2 during fuel rationing. But it cannot replace oil as the engine of agriculture - current farming methods would require all of the grain produced to be converted to ethanol for next year's operations - hardly sustainable.
Oil, by comparison, cost (in terms of production, refining, and transport costs) about 1 litre per 100 in its early years - almost free energy. Now it is about 1 litre to produce 14, still streets ahead of anything else, including ethanol. It may buy us a little time to think, which we will probably waste - that is all.
