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† depending on production method In order to create ethanol, all biomass needs to go through some of these steps: it needs to be grown, collected, dried, fermented, and burned. All of these steps require resources and an infrastructure. The ratio of the energy released by burning the resulting ethanol fuel to the used energy in the process, is known as the ethanol fuel energy balance (sometimes called "Net energy gain") and studied as part of the wider field of energy economics. Figures compiled in a 2007 National Geographic Magazine article 〔 point to modest results for corn ethanol produced in the US: 1 unit of energy input equals 1.3 energy units of corn ethanol energy. The energy balance for sugarcane ethanol produced in Brazil is much more favorable, 1 to 8. Over the years, however, many reports have been produced with contradicting energy balance estimates. A 2006 University of California Berkeley study, after analyzing six separate studies, concluded that producing ethanol from corn uses marginally less petroleum than producing gasoline.〔Sanders, Robert (January 26, 2006).(Ethanol can replace gasoline with significant energy savings, comparable impact on greenhouse gases ). ''University of California Berkeley'' Energy Resources Group, Dan Kammen and Alex Farrell; Michael O'Hare, Goldman School of Public Policy. Also published 27 JANUARY 2006 VOL 311 Science, www.sciencemag.org .Retrieved August 22, 2011.〕 ==Energy balance reports== In 1995 the USDA released a report stating that the net energy balance of corn ethanol in the United States was an average of 1.24. It was previously considered to have a negative net energy balance. However, due to increases in corn crop yield and more efficient farming practices corn ethanol had gained energy efficiency 〔''Estimating the Net Energy Balance of Corn Ethanol'' Hosein Shapouri, James A. Duffield, and Michael S. Graboski Agricultural Economics Report No. (AER721) 24 pp, July 1995 http://www.ers.usda.gov/media/926108/aer721.pdf〕 Ken Cassman, a professor of agronomy at the University of Nebraska–Lincoln, said in 2008 that ethanol has a substantial net positive direct energy balance—1.5 to 1.6 more units of energy are derived from ethanol than are used to produce it. Comparing 2008 to 2003, Alan Tiemann of Seward, a Nebraska Corn Board member, said that ethanol plants produce 15 percent more ethanol from a bushel of corn and use about 20 percent less energy in the process. At the same time, corn growers are more efficient, producing more corn per acre and using less energy to do so.〔(UNL study: Ethanol energy efficiency growing ) - 29. September 2008〕 Opponents of corn ethanol production in the U.S. often quote the 2005 paper 〔''Ethanol Production Using Corn, Switchgrass, and Wood; Biodiesel Production Using Soybean and Sunflower'' David Pimentel and Tad W. Patzek Natural Resources Research, Vol. 14, No. 1, March 2005 ()〕 of David Pimentel, a retired Entomologist, and Tadeusz Patzek, a Geological Engineer from UC Berkeley. Both have been exceptionally critical of ethanol and other biofuels. Their studies contend that ethanol, and biofuels in general, are "energy negative", meaning they take more energy to produce than is contained in the final product. A 2006 article 〔''Ethanol Can Contribute to Energy and Environmental Goals'' Alexander E. Farrell, Richard J. Plevin, Brian T. Turner, Andrew D. Jones, Michael O’Hare, Daniel M. Kammen 506 27 January 2006 vol 311 Science http://rael.berkeley.edu/ebamm/FarrellEthanolScience012706.pdf〕 in Science offers the consensus opinion that current corn ethanol technologies had similar greenhouse gas emissions to gasoline, but was much less petroleum-intensive than gasoline. Fossil fuels also require significant energy inputs which have seldom been accounted for in the past. Ethanol is not the only product created during production. By-products also have energy content. Corn is typically 66% starch and the remaining 33% is not fermented. This unfermented component is called distillers grain, which is high in fats and proteins, and makes a good animal feed supplement.〔http://www.ddgs.umn.edu/more.htm University of Minnesota〕 In 2000, Dr. Michael Wang, of Argonne National Laboratory, wrote that these ethanol by-products are the most contentious issue in evaluating the energy balance of ethanol. He wrote that Pimentel assumes that corn ethanol entirely replaces gasoline and so the quantity of by-products is too large for the market to absorb, and they become waste. At lower quantities of production, Wang finds it appropriate to credit corn ethanol based on the input energy requirement of the feed product or good that the ethanol by-product displaces.〔(Corn-Based Ethanol Does Indeed Achieve Energy Benefits )〕 In 2004, a USDA report found that co-products accounting made the difference between energy ratios of 1.06 and 1.67.〔(The 2001 Net Energy Balance of Corn-Ethanol )〕〔(The Energy Balance of Corn Ethanol: An Update )〕 In 2006, MIT researcher Tiffany Groode came to similar conclusions about the co-product issue.〔(Review of Corn Based Ethanol Energy Use and Greenhouse Gas Emissions )〕 In Brazil where sugar cane is used, the yield is higher, and conversion to ethanol is more energy efficient than corn. Recent developments with cellulosic ethanol production may improve yields even further.〔http://news.bbc.co.uk/2/hi/science/nature/5353118.stm Biofuels look to the next generation〕 In 2006 a study from the University of Minnesota found that corn-grain ethanol produced 1.25 units of energy per unit put in. A 2008 study by the University of Nebraska found a 5.4 energy balance for ethanol derived specifically from switchgrass.〔''Grass biofuels 'cut CO2 by 94% Reprted on bbc.co.uk http://news.bbc.co.uk/2/hi/science/nature/7175397.stm〕〔M. R. Schmer, K. P. Vogel, R. B. Mitchell, and R. K. Perrin ''Net energy of cellulosic ethanol from switchgrass'' PNAS published January 7, 2008, 〕 This estimate is better than in previous studies and according to the authors partly due to the larger size of the field trial (3-9 ha) on 10 farms. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ethanol fuel energy balance」の詳細全文を読む スポンサード リンク
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