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

intended to help fuel producers estimate the lifecycle greenhouse gas emissions and fossil
energy use for all stages in the development of their specific fuel. EPA will evaluate
whether the FUEL-CO2 model would be an appropriate tool for fuel providers who wish
to demonstrate their actual reductions in greenhouse gas emissions and fossil energy use.
This may also be the best way for ethanol producers to quantify the benefits of their
renewable process energy use when qualifying corn ethanol as cellulosic biomass ethanol
(an option for ethanol producers, stipulated in the Act).
1. Modifications To GREET Assumptions
GREET is subject to periodic updates by ANL, each of which results in some
changes to the inputs and assumptions that form the basis for the lifecycle estimates of
emissions generated and energy consumed. These updates generally focus on those input
values for those fuels or vehicle technologies that are the focus of ANL at the time. As a
result there are a variety of other inputs related to ethanol and biodiesel that have not
been updated in some time. In the context of the RFS program, we determined that some
of the GREET input values that were either based on outdated information or did not
appropriately reflect market conditions under a renewable fuels mandate should be
examined more closely, and updated if necessary.
In the timeframe available for developing this proposal, we chose to concentrate
our efforts on those GREET input values for ethanol that had significant influence on the
lifecycle emissions or energy estimates and that were likely to be based on outdated
information. We reviewed the input values only for ethanol made from corn, since this
particular renewable fuel is likely to continue to dominate the renewable fuel pool
through at least 2012. For cellulosic ethanol and biodiesel the GREET default values
were used in this proposal. However, we have also initiated a contract with ANL to
investigate a wider variety of GREET input values, including those associated with the
following fuel/feedstock pathways:
• Ethanol from corn
• Ethanol from cellulosic materials (hybrid populars, switchgrass, and corn stover)
• Biodiesel from soybean oil
• Methanol from renewable sources
• Natural gas from renewable sources
• Renewable diesel formulations
The contract focuses on the potential fuel production developments and efficiency
improvements that could occur within the time-frame of the RFS program. The GREET
input value changes resulting from this work are projected to be available in the fall of
2006, not in time for this proposal, but they will be incorporated into revised lifecycle
assessments for the final rule.
We did not investigate the input values associated with the production of
petroleum-based gasoline or diesel fuel in the GREET model for this proposal. However,
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