The most controversial issue about ethanol is whether its use is actually a good idea, and therefore worthy of public policy support and environmental endorsement.
Two questions come up again and again:
1. Does the production of ethanol actually yield more energy than is consumed in the process of producing it?
2. Does the use of ethanol in transportation fuels actually reduce emissions?
A recent study by Argonne National Laboratory provides a seemingly convincing case that the answers to these two questions are “Yes” and “Yes”.
The study also shows how much better “cellulosic” ethanol approaches are than conventional “corn” (i.e., starch) ethanol approaches. Whereas corn ethanol requires about 0.8 Btu of non-renewable (fossil) energy input for each Btu of energy output, cellulosic ethanol requires only about 0.1 Btu of fossil energy input for each Btu of energy output. (There’s no need to count the “solar” energy associated with growing the feedstock, because it’s totally free.) Correspondingly, the use of corn ethanol reduces greenhouse gases (GHGs) by about 20-30% relative to conventional gasoline, whereas cellulosic ethanol offers a 85% reduction in GHG emissions.
Although these two entry-level questions can now largely be dispensed with, there are other issues that remain important for ethanol. One is the economics. According to one industry analyst I’ve talked with, corn ethanol is not a very economically-attractive way of reducing GHGs, with an incremental cost of about $300/ton CO2 reduction — much higher than most other emission reduction alternatives. (Of course, the government’s promotion of ethanol is more for reducing oil consumption/imports than emissions.) The economics of cellulosic may be more promising, but are more uncertain.
The other key remaining issue for ethanol is how much of a dent it can make in the nation’s overall petroleum/gasoline requirements. Is there enough land (enough growth potential) to supply a large portion of motor fuel demand? I’ve heard that corn ethanol could supply perhaps high single digits of U.S. gasoline requirements, implying intuitively that cellulosic ethanol might be able to supply a share several times greater. Anyone?