Ethanol Can Contribute to Energy and Environmental Goals
Alexander E. Farrell1*,
Richard J. Plevin1,
Brian T. Turner1,2,
Andrew D. Jones1,
Michael O'Hare2 and
Daniel M. Kammen1,2,3
1 Energy and Resources Group, University of California, Berkeley, CA 94720–3050, USA.
2 Goldman School of Public Policy, University of California, Berkeley, CA 94720–3050, USA.
3 Renewable and Appropriate Energy Laboratory, University of California, Berkeley, CA 94720–3050, USA.
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Fig. 1. (A) Net energy and net greenhouse gases for gasoline, six studies, and three cases. (B) Net energy and petroleum inputs for the same. In these figures, small light blue circles are reported data that include incommensurate assumptions, whereas the large dark blue circles are adjusted values that use identical system boundaries. Conventional gasoline is shown with red stars, and EBAMM scenarios are shown with green squares. Adjusting system boundaries reduces the scatter in the reported results. Moreover, despite large differences in net energy, all studies show similar results in terms of more policy-relevant metrics: GHG emissions from ethanol made from conventionally grown corn can be slightly more or slightly less than from gasoline per unit of energy, but ethanol requires much less petroleum inputs. Ethanol produced from cellulosic material (switchgrass) reduces both GHGs and petroleum inputs substantially.
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Fig. 2. Alternative metrics for evaluating ethanol based on the intensity of primary energy inputs (MJ) per MJ of fuel and of net greenhouse gas emissions (kg CO2-equivalent) per MJ of fuel. For gasoline, both petroleum feedstock and petroleum energy inputs are included. "Other" includes nuclear and hydrological electricity generation. Relative to gasoline, ethanol produced today is much less petroleum-intensive but much more natural gas– and coal-intensive. Production of ethanol from lignite-fired biorefineries located far from where the corn is grown results in ethanol with a high coal intensity and a moderate petroleum intensity. Cellulosic ethanol is expected to have an extremely low intensity for all fossil fuels and a very slightly negative coal intensity due to electricity sales that would displace coal.
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