CommunicationRenewable corn-ethanol and energy security
Introduction
The debate surrounding the sensibility of ethanol has taken on a new urgency as the government increases subsides and more actively promotes ethanol as a sustainable, more secure alterative to gasoline. Though the process of producing ethanol from corn was originally believed to use more energy than it created (Chambers et al., 1979), farming and ethanol-conversion processes have since become more efficient and the number of researchers arguing that the net-energy value (NEV) is positive has grown. The purpose of this study is not to contribute to the NEV debate, but instead to investigate to what extent renewable ethanol can meet our energy security goals. We do so by modeling the ethanol-production process as a renewable one where energy inputs come from ethanol rather than fossil fuels. We then calculate how much gasoline such a process could displace. Finally, we analyze the reliability of the supply of ethanol. Though reliability should obviously be a central component of an energy security policy, researchers and policy makers have paid little attention to this quality when evaluating ethanol.
Section snippets
Background and literature review
Table 1 reports results for eight studies estimating the energy required to grow corn, transport it to an ethanol plant, convert it to ethanol, and finally transport the ethanol to fueling stations. The NEV of ethanol is the difference between the energy contained in a liter of ethanol and the energy required to produce and distribute it. The estimates range from −1.5 to 0.9 MJ/L. The wide variance can be explained by difference in the underlying assumptions. For instance, some studies add an
Methods
The assumptions underlying our analysis are based on the findings of a 2002 USDA study conducted by Shapouri, Duffield, and Wang (SDW). Table 1 shows that this study estimated about the highest NEV and, consequently, it is widely cited by ethanol proponents. Though the study's methodology has been criticized by Patzek et al. (2005) and Pimentel (2003), we use the findings of SDW both as a means of presenting a bounding argument and because it is reasonable to evaluate the government's policy of
Conclusion
Before analyzing the sensibility of a particular fuel source, it is first necessary to clarify the overall objectives. For instance, if the objective of promoting ethanol is to rely more on domestic fossil fuels, then perhaps it would be more efficient to use natural gas and liquefied coal to power cars directly—compatible vehicles have already been operating for years on US roadways and we would not disrupt the food supply. If, however, the objective is to power cars with a sustainable,
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