With skyrocketing petroleum prices and war in the oil-producing nations of the Middle East, biofuels are increasingly touted as desirable alternatives to petroleum. But can they really help free us from a petroleum economy? How do they compete with conventional fuels and each other on a cost basis? What are the environmental impacts? Researchers at the University of Minnesota have published a wide-ranging study that offers some answers.
Currently, corn grain ethanol and soybean biodiesel are the two predominant alternative transportation fuels in the United States. Both can be used in conventional car and truck engines in blended form, and biodiesel can also be used in pure form ("B100"). Both are available at an increasing number of wholesale and retail locations across the nation. However, both require significant energy to produce, have their own environmental impacts, and could divert corn and soybeans from the nation's food supply. Exactly what the energy balance and environmental impacts are and whether these fuels should be subsidized has been the subject of heated debate among scientists, policy makers, and the public.
Researchers from the University of Minnesota and St. Olaf College led by ecology professor G. David Tilman hoped to inform this debate by conducting a comprehensive analysis of the full life cycles of these biofuels. According to the study, published in the 25 July 2006 issue of the Proceedings of the National Academy of Sciences, a viable alternative fuel must meet four criteria: show superior environmental benefits over the fossil fuel it displaces, be economically competitive with that fossil fuel, be producible in sufficient quantities to make a meaningful impact on energy demands, and provide a net energy gain over the energy sources used to produce it.
Comparison: The Study Findings
The authors performed their analysis using public data on farm yields, commodity and fuel prices, farm energy and chemical inputs, production plant efficiencies, production of coproducts (e.g., an animal feed known as distillers dried grains with solubles, or DDGS), greenhouse gas emissions, and other environmental effects. The boundaries the authors established in accounting for energy inputs were larger than in other studies, including, for example, the energy required to manufacture the machinery used to farm corn and soybeans.
The analysis showed that both corn grain ethanol and soybean diesel have a positive net energy balance (NEB), with ethanol having a 25% NEB and biodiesel a 93% NEB. That is,...