Pimentel spoke to a largely proethanol crowd of corn producers and their representatives. Ethanol, he said, is not a true renewable energy source, because it requires more energy in its production than is extracted from the finished product. According to his calculations, ethanol takes about 1.15 BTUs (British Thermal Units) of input for every 1 BTU of output.
I'm not sure where he's getting his numbers, but the only phase that require significant amount of energy input is the distillation. However, significant portion of that heat can be recaptured.
Lastly, then how come that Brazil is making so much ethanol to be used as a fuel? Source doesn't really matter because the distillation is the same in both cases whether one start with starch or sugar. Or is there a cheaper way to separate alcohol from water?