Net energy debate
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Bioenergy > Issues > Controversies > Net energy debate
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One of the controversies surrounding biofuels is the question of net energy (also referred to as "energy balance"). Net energy compares the energy value of the fuel produced with all of the energy inputs that went in: nitrogen fertilizer (often made from petroleum, the fuel that powered the tractors, trucks and other machines, and the energy source for the plant that produced the fuel. It also takes into account the energy value of the co-products from production. Net energy value is not intrinsic to a certain fuel or feedstock but is heavily influenced by the efficiency of the industry and the technologies used. Net energy is usually calculated by using some form of life-cycle analysis.
US Corn ethanol
The US corn ethanol industry has seen debate over whether the net energy balance is positive.
- MIT analysis of corn ethanol says net-energy can go either way 8 January 2007 from MIT news office. The analysis shows that the energy balance of corn ethanol is so close that several factors can easily change whether it ends up a net energy winner or loser, while cellulosic ethanol was positive. In all cases there was a reduction in oil consumption.
- Biofuel Skeptic Extraordinaire: An interview with David Pimentel 08 Dec 2006 from The Grist. David Pimentel, professor emeritus of entomology at Cornell University has been a critic of corn ethanol since the 1970's
- Net Energy Balance for Bioethanol Production and Use US Department of Energy Energy Efficiency and Renewable Energy Department (EERE).
- Estimating the Net Energy Balance of Corn Ethanol (PDF) by Hosein Shapouri, James A. Duffield, and Michael S. Graboski. U.S. Department of Agriculture, Economic Research Service, Office of Energy. Agricultural Economic Report No. 721, July 1995.
Switchgrass
- Grass biofuels 'cut CO2 by 94%', 8 January 2008, by BBC News: A new report by US researchers has found that fast-growing "switchgrass-derived ethanol produced 540% more energy than was required to manufacture the fuel" and "delivers vast savings of carbon dioxide emissions compared with petrol." The paper, "Net energy of cellulosic ethanol from switchgrass (PDF file)" in the Proceedings of the National Academy of Sciences, analyzed all of the energy input factors, including "nitrogen fertiliser, herbicides, diesel and seed production."
- "Second-generation" biofuels, such as grass-derived cellulosic ethanol, "could produce much higher energy yields per tonne [than food crops such as corn] because it utilised the whole plant rather than just the seeds."
Resources
- The Energetics of Ethanol: An Introduction and Link to Studies -This page offers an excellent outline of the controversy and links to a number of studies.
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