Biofuels Can't Solve Energy Problem

A comparative analysis of the life cycles of two popular fuel additives by researchers at the University of Minnesota shows that biodiesel has a much higher net energy benefit than ethanol, but neither can do much to meet the growing U.S. energy demand.

The study concludes that both corn-grain-derived ethanol and soybean-based biodiesel produce more energy than is needed to grow the crops and convert them into biofuels. However, the amount of energy each returns differs greatly. Biodiesel returns 93% more energy than is used to produce it, whereas ethanol currently provides only 25% more energy, according to the study.

"Quantifying the benefits and costs of biofuels throughout their life cycles allows us not only to make sound choices today but also to identify better biofuels for the future," says Jason Hill, lead author of the study, which appears in Proceedings of the National Academy of Sciences (2006, 103, 11206).

The researchers caution that neither biofuel can come close to meeting the growing demand for alternatives to petroleum. Converting all current U.S. corn and soybean production to biofuels would satisfy only 12% of gasoline demand and 6% of diesel usage, they conclude. Meanwhile, global population growth and increasingly affluent societies will increase demand for corn and soybeans for food.

The study says the environmental impacts of the two biofuels also differ. Biodiesel produces 41% fewer greenhouse gas emissions than diesel fuel, whereas ethanol produces 12% fewer greenhouse gas emissions than gasoline. Soybeans also require much less nitrogen fertilizer and pesticides than corn, the study notes.

The researchers say that rising gasoline and diesel prices have made the development of biofuels more economically advantageous and that biodiesel's environmental benefits seem strong enough to merit subsidy. Ethanol also plays an important role as an additive by oxygenating gasoline and making it burn more cleanly.

"We did this study to learn from ethanol and biodiesel," says David Tilman, a study coauthor. "Producing biofuel for transportation is a fledgling industry. Corn ethanol and soybean biodiesel are successful first-generation biofuels. The next step is a biofuel crop that requires low chemical and energy inputs and can give us much greater energy and environmental returns."

The study points to nonfood plants that can grow on marginal lands with minimal input of fertilizers and pesticides as the best hope for biomass-based energy. Prairie grasses and woody plants, as well as agricultural and forestry wastes, have the potential to provide much larger biofuel supplies with greater environmental benefits than corn-produced ethanol and biodiesel from soybeans, according to the Minnesota researchers.