There's a lot of loose talk these days about stretching US fuel supplies with alcohol. But the country would be wise to take a hard look at the real payoffs before jumping into a massive gasohol program. The supposed energy gains could be illusory.
For example, J. W. Day Jr. of Louisiana State University and his colleague C. S. Hopkinson Jr. (now at the University of Georgia) have done this using alcohol made from Louisiana sugar cane as their model. their conclusion as stated in their report in Science: "Alcohol from crops produced in excess of food requirements will not make a significant contribution to national energy needs."
Given the energy intensive way Americans grow crops, they would be fortunate to break even on alcohol production, let alone realize any worthwhile energy gain. How then, is Brazil able to make sugar cane alcohol pay off?
Day and Hopkinson point out that the main energy inputs -- fuel, machinery, nitrogen fertilizer -- represent only 83 percent of the energy consumed in Brazilian alcohol production compared with 90 percent in Louisiana. On the other hand, labor (muscle energy) accounts for 3 percent of Brazil's energy input but less than 0.3 percent in Louisiana. As a result, Brazil gets a 240 percent net energy gain (over fossil-fuel input) in its alcohol production.
The best return Day and Hopkinson would expect in Louisiana would be 80 percent, if sugar cane waste (bagasse) were used to generate steam to distill the alcohol. If fossil fuel were used, as might well be the case, the gain would turn into a 10 percent net energy loss. Plants currently under design would burn a 50-50 bagasse-fossil fuel mix, yielding an expected 20 percent energy profit. "Such a small return on energy investment is not likely to help solve the national energy problem," the scientists note.
To some extent, this analysis should itself be taken with reservation.R. S. Chambers, R. A. Herendeen, J. J. Joyce, and P. S. Penner of the University of Illinois pointed out in a comprehensive analysis in Science last November that estimated alcohol payoffs depend strongly on the analyst's assumptions. What milage gain or loss over gasoline is expected? What are the actual energy inputs? If coal is the fossil fuel used, is there not a "gain" in saving oil? "There is no simple answer to the question of net energy from gasohol," they conclude.
Nevertheless, this doesn't undercut the main Day-Hopkinson point that their analysis emphasizes "the importance of site-specific energy balance evaluations of crops used for alcohol production."
If the US is to profit from gasohol, it will have to keep careful account of the energy balance and be willing to change some of its energy-wasting agricultural ways. As the Day-Hopkinson study illustrates, there is no easy way to make alcohol production worthwhile.