Ethanol fuel energy balance

Ethanol fuel energy balance

† depending on production method

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 total amount of energy input into the process compared to the energy released by burning the resulting ethanol fuel 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 current energy equals 1.3 energy units of corn ethanol energy. The energy balance for sugarcane ethanol produced in Brazil is more favorable, 1:8. Over the years, however, many reports have been produced with contradicting energy balance estimates.

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]

Cassman, a Heuermann Professor of Agronomy at the university, said 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. Compared to just five years ago, Tiemann said, 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.

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 DOI|10.1007/s11053-005-4679-8 [ ] ] 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 ] 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. Furthermore, it should be pointed out that fossil fuels also require significant energy inputs which have seldom been accounted for in the past.

It is also important to note that ethanol is not the only product created during production, and the energy content of the by-products must also be considered. 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 good animal feed. [ University of Minnesota]

Back 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] ] . 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 somewhat more energy efficient than corn. Recent developments with cellulosic ethanol production may improve yields even further. [ 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. [cite journal | first = Jason | last = Hill | coauthors = Nelson, Erik; Tilman, David; Polasky, Stephen; and Tiffany, Douglas | year = 2006 | month = July 25 | title = Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels | journal = Proceedings of the National Academy of Sciences | volume = 103 | issue = 30 | pages = 11206–10 | doi = 10.1073/pnas.0604600103 | url = | accessdate = 2007-01-24 | pmid = 16837571]

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 ] [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"', DOI|10.1073/pnas.0704767105 ] . 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.


According to DoE, [ [ DoE: Biomass Program: Net Energy Balance for Bioethanol Production and Use] Quote: "...The most official study of the issue, which also reviews other studies, concludes that the "net energy balance" of making fuel ethanol from corn grain is 1.34...For cellulosic bioethanol—the focus of the Biomass Program—that study projects an energy balance of 2.62...A Biomass Program life-cycle analysis of producing ethanol from stover, now underway, is expected to show a very impressive net energy ratio of more than 5..."] to evaluate the net energy of ethanol four variables must be considered:
# the amount of energy contained in the final ethanol product
# the amount of energy directly consumed to make the ethanol (such as the diesel used in tractors)
# the quality of the resulting ethanol compared to the quality of refined gasoline
# the energy indirectly consumed (in order to make the ethanol processing plant, etc).

Much of the current academic discussion regarding ethanol currently revolves around issues of system borders. This refers to how complete of a picture is drawn for energy inputs. There is debate on whether to include items like the energy required to feed the people tending and processing the corn, to erect and repair farm fences, even the amount of energy a tractor represents.

In addition, there is no consensus on what sort of value to give the rest of the corn (such as the stalk), commonly known as the 'coproduct.' Some studies leave it on the field to protect the soil from erosion and to add organic matter, while others take and burn the coproduct to power the ethanol plant, but do not address the resulting soil erosion (which would require energy in the form of fertilizer to replace). Depending on the ethanol study you read, net energy returns vary from .7-1.5 units of ethanol per unit of fossil fuel energy consumed. For comparison, that same one unit of fossil fuel invested in oil and gas extraction (in the lower 48 States) will yield 15 units of gasoline, a yield an order of magnitude better than current ethanol production technologies, ignoring the energy quality arguments above and the fact that the gain (14 units) is not carbon neutral. ["Net Energy From the Extraction of Oil and Gas in the United States" Cutler J. Cleveland (pdf)]

In this regard, geography is the decisive factor. In tropical regions with abundant water and land resources, such as Brazil and Colombia, the viability of production of ethanol from sugarcane is no longer in question; in fact, the burning of sugarcane residues (bagasse) generates far more energy than needed to operate the ethanol plants, and many of them are now selling electric energy to the utilities. However, while there may be a positive net energy return at the moment, recent research suggests that the sugarcane plantations are not sustainable in the long run, as they are depleting the soil of nutrients and carbon matter Fact|date=January 2008 Did they return the ashes from their plants to the land in the recent research?

The picture is different for other regions, such as most of the United States, where the climate is too cool for sugarcane. In the U.S., agricultural ethanol is generally obtained from grain, chiefly corn. But it can also be obtained from cellulose, more energy balanced bioethanol.

Clean production bioethanol

Clean production bioethanol Fact|date=January 2008 is a biofuel obtained using as much as possible non-greenhouse gas renewable energy sources:
* the amount of energy directly consumed to make the ethanol is renewable energy : the tractor uses ethanol engine, biodiesel, air engine or electricity obtained from wind or solar energy.
* the energy indirectly consumed, that can be solar energy.To transport the biofuel to the fuel-stations can be used truck with ethanol engines or electric motors (that uses energy solar energy stored in the batteries).


ee also

* Biobutanol
* Energy balance
* Ethanol fuel
* Starch

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