A lot of ethanol do not rely on fossil fuels for heat. They use other plant byproducts.

When we burn fossil fuels, we release carbon that was stored in the earth for hundereds of millions of years, and would naturally take a very long time before it ever reached the atmosphere. Essentially, we're adding new carbon to the atmosphere. With biofuels, the plants intake CO2 as they grow, releasing O2. When we burn the biofuels and plant matter, the CO2 is released, to be soaked up again with next years crop.

I guess it comes down to, what is more efficient? A solar cell, or a leaf? I'm guessing the leaf...