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
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 website, 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.
2005. Report at the 15th International Symposium on Alcohol Fuels