Regulation of Fuels and Fuel Additives: Renewable Fuel Standard ...

a researcher concludes that the net energy balance is negative, or the energy efficiency is
less than 1.0. Such cases would indicate that the fossil energy used in the production and
transportation of ethanol exceed the energy in the ethanol itself, and this is generally
interpreted to mean that lifecycle fossil fuel use negates the benefits of replacing gasoline
with ethanol. However, since the metrics used do not actually compare ethanol to
gasoline, such interpretations are unwarranted.
The primary studies that conclude that the energy balance is negative were
conducted by Dr. David Pimental of Cornell University and Dr. T. Patzek of University
of California, Berkeley 90,91 . Many other researchers, however, have criticized that work
as being based on out-dated farming and ethanol production data, including data not
normally considered in lifecycle analysis for fuels, and not following the standard
methodology for lifecycle analysis in terms of valuing co-products. Furthermore, several
recent surveys have concluded that the energy balance is positive, although they differ in
their numerical estimates.
92, ,
93 94 Authors of the GREET model have also concluded that
the lifecycle amount of fossil energy used to produce ethanol is less than the amount of
energy in the ethanol itself. Based on our review of all the available information, we
have concluded that the energy balance is indeed positive, and we believe that the
GREET model provides an accurate basis for quantifying the lifecycle impacts.
B. Overview Of Methodology
The GREET model does not provide estimates of energy consumed and emissions
generated in total, such as the total amount of natural gas consumed in the U.S. in a given
year by ethanol production facilities. Instead, it provides estimates on a national average,
per fuel unit basis, such as the amount of natural gas consumed for the average ethanol
production facility per million Btus of ethanol produced. As a result we could not use
GREET directly to estimate the nationwide impacts of replacing some gasoline and diesel
with renewable fuels.
Instead, we used GREET to generate comparisons between renewable fuels and
the petroleum-based fuels that they displace. These comparisons allowed us to develop
displacement indexes that represent the amount of lifecycle GHGs or fossil fuel reduced
when a Btu of renewable fuel replaces a Btu of gasoline or diesel. In order to estimate
the incremental impacts of increased use of renewable fuels on GHGs and fossil fuels, we
90 Pimentel, David “Ethanol Fuel: Energy Balance, Economics, and Environmental Impacts are Negative”,
Vol. 12, No 2, 2003 International Association for Mathematical Geology, Natural Resources Research
91 Pimentel, D.; Patzek, T. "Ethanol production using corn, switchgrass, and wood; biodiesel production
using soybean and sunflower." Nat. Resour. Res. 2005, 14 (1), 65-76.
92 Hammerschlag, R. "Ethanol's Energy Return on Investment: A Survey of the Literature 1990 - Present."
Environ. Sci. Technol. 2006, 40, 1744 - 1750.
93 Farrell, A., Pelvin, R., Turner, B., Joenes, A., O’Hare, M., Kammen, D., “Ethanol Can Contribute to
Energy and Environmental Goals”, Science, 1/27/2006, Vol 311, 506-508
94 Hill, J., Nelson, E., Tilman, D., Polasky, S., Tiffany, D., “Environmental, economic, and energetic costs
and benefits of biodiesel and ethanol biofuels”, Proceedings of the National Academy of Sciences,
7/25/2006, Vol. 103, No. 30, 11206-11210
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