In the survey, ethanol producers were asked to respond to questions about ethanol yield (undenatured) per bushel of corn and energy used in the plants. The 2008 updates presented in the report recorded the effects of current practices used by corn producers and ethanol processors.
This report measures all conventional fossil fuel energy used in the production of 1 gallon of corn ethanol. For every British Thermal Unit (B.T.U.) of energy required to make ethanol, 2.3 B.T.U.s of energy are produced. The ratio is somewhat higher for some firms that are partially substituting biomass energy in processing energy. Since the last study in 2004, the net energy balance of corn ethanol has increased from 1.76 B.T.U.s to 2.3 B.T.U.s of required energy, U.S.D.A. said.
Overall, ethanol has made the transition from an energy sink, to a moderate net energy gain in the 1990s, to a substantial net energy gain in the present, the study indicates. And there are still prospects for improvement. Ethanol yields have increased by about 10% in the last 20 years, so proportionately less corn is required. In addition to refinements in ethanol technology, corn yields have increased by 39% over the last 20 years, requiring less land to produce ethanol.
Authors of the study are H. Shapouri, agricultural economist, Office of Energy Policy and New Uses, Office of the Chief Economist, U.S.D.A.; Paul Gallagher, associate professor, Economics Department, Iowa State University; Ward Nefstead, associate professor, Applied Economics Department, University of Minnesota; Rosalie Schwartz, program and recruitment director, Agricultural Economics Department, University of Nebraska (Lincoln); Stacey Noe, program coordinator, Agricultural Entrepreneurship Initiative, Iowa State University; and Roger Conway, former director, Office of Energy Policy and New Uses, Office of the Chief Economist, U.S.D.A.
The study can be found at www.usda.gov/oce/reports/index.htm.