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Lifecycle Energy Balance

The fossil "energy balance" of ethanol has been the subject of debate despite the fact that this metric is not as useful to policymakers as "lifecycle GHG emissions" or "lifecycle petroleum balance." As shown in the figure below, past estimates vary as to how much ethanol reduces fossil-fuel use. The 16 studies above the zero line show that ethanol contains more energy than the fossil-based energy used to produce it. The nine studies below the zero line say that ethanol is a net fossil energy loss. It should be noted that all studies listed in the figure below the zero line were either done before 1993 or in some combination by the Pimentel and Patzek team.

Comparative Results of Corn Ethanol Fossil Energy Balance Studies

Chart showing comparative results of corn ethanol fossil energy balance studies. The x-axis is year, from 1978 to 2007. The y-axis is net energy value in btu/gallon. Sixteen studies show a positive energy balance. Nine studies show a negative energy balance. The studies are plotted approximately as follows: Chambers et al., 1979, -95,000 btu/gallon; Weinblatt et al., 1982, -8,000; Ho, 1989, -2,000; Marland & Turnollow, 1990, +20,000; Pimentel, 1991, -35,000; Keeney & DeLuca, 1992, -4,000; Lorenz & Morris, 1995, +32,000; Shapouri et al., 1995, +19,000; Agri. & Agri Food Canada, 1999, +32,000; Wang et al., 1999, +21,000; Pimentel, 2001, -31,000; Shapouri et al., 2002, +22,000; Kim & Dale, 2002, +21,000; Graboski, 2002, +19,000; Wang, 2003, +22,000; Delucchi, 2003, +19,000; Pimentel, 2003, -21,000; Patzek, 2003, -62,000; Shapouri et al., 2004, +32,000; NR Canada, 2005, +41,000; Kim & Dale, 2005, +22,000; Pimentel & Patzek, 2005, -20,000; Hill, 2006, +20,000; Farrell, 2006, +19,000; Wang, 2006, +18,000.

Source: Ethanol: The Complete Energy Lifecycle Picture (PDF 12.1 MB) Download Adobe Reader.

The considerable differences between these studies have prompted two teams to compare a subset of the existing studies to find the reasons for the differences and draw conclusions of their own.

One study, Ethanol Can Contribute to Energy and Environmental Goals, published by Science magazine, points out that evaluations reporting negative net energy for ethanol incorrectly ignored coproducts and used obsolete data.

Another study, Ethanol's Energy Return on Investment: A Survey of the Literature 1990-Present, available on the ACS Publications Web site, points out that gasoline does not have a net energy value of zero as often assumed in fossil energy balance discussions. Only 76% of its embodied fossil energy is delivered to the end user, which would place it well below the Pimentel studies on the chart above. This is because so much energy is used to extract, transport, and refine oil and gasoline.

When these two factors are taken into account, corn-based ethanol shows a clear benefit over gasoline. The size of this benefit also depends on the feedstock used and how the ethanol plant is powered, as shown above.

Chart showing total BTU spent for one BTU available at the pumps. It shows both the fossil energy, petroleum energy, and the total and shows BTUs in the fuel as well as BTUs used in production. The fuels in the chart include: gasoline, current corn ethanol, corn ethanol using natural gas, corn ethanol using coal, and cellulosic ethanol.

Source: Updated Energy and Greenhouse Gas Emission Results of Fuel Ethanol. 2005. Report at the 15th International Symposium on Alcohol Fuels (PDF 1.7 MB) Download Adobe Reader.