Not worth the trouble

Turning plants such as corn, soybeans and sunflowers into fuel uses much more energy than the resulting ethanol or biodiesel generates, according to a new

and University of California-Berkeley study.

"There is just no energy benefit to using plant biomass for liquid fuel," says David Pimentel, professor of ecology and agriculture at Cornell.

Pimentel and Tad W. Patzek, professor of civil and environmental engineering at Berkeley, conducted a detailed analysis of the energy input-yield ratios of producing ethanol from corn, switch grass and wood biomass as well as for producing biodiesel from soybean and sunflower plants.

In terms of energy output compared with energy input for ethanol production, the study found that corn requires 29% more fossil energy than the fuel produced; switch grass requires 45% more fossil energy than the fuel produced; and wood biomass requires 57% more fossil energy than the fuel produced.

In terms of energy output compared with the energy input for biodiesel production, the study found that soybean plants requires 27% more fossil energy than the fuel produced, and sunflower plants requires 118% more fossil energy than the fuel produced.