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| Fig. 1: E85 Fuel Pump. (Source: Wikimedia Commons) |
Ethanol has been proposed as a substitute for gasoline in order to move the country away from using fossil fuels. Ethanol is said to be much cleaner than other forms of fuels however, it takes a substantial amount of energy to produce. There is a misconception based on data from the 1980s that production of ethanol consumes more energy than the fuel actually contains making the fuel inefficient and costly to our environment. However, given more recent data we can see that this is not the case. [1]
The majority of energy consumed during the production of ethanol comes from production of the corn.. The largest proportion of all the energy used during the growing, cultivating, and harvesting process is for fertilizer. [1] The USDA published that in 2005 the average energy in BTU/bushel of corn for nitrogen fertilizer was 20,464 BTUs out of the total 41,029BTUs needed to produce a bushel of corn. That makes nitrogen a little under 50% of all the energy used to grow corn for ethanol. [2] It is important to note that this is the energy is used to grow all parts of the corn even though only the starch (66%) of the corn is used to produce ethanol. [1] The other 50% of energy is used towards farm vehicles, crop drying, on farm electricity, bulk transport, and irrigation to name the main players. [2] Converting the total BTUs per bushel to BTUs per gallon we get 14,866 BTUs/gal.
Both dry and wet milling processes are use in the production of ethanol nationwide, with trade offs in energy consumption and useful co-products. [3] Unsurprisingly the majority of energy used during this part of the process comes from steam processes during the ethanol conversion stage. 49,733 BTUs/gal are used during this process. Adding on a corn transport of 2,120 1BTus/gal and the distributions energy of 1,487 BTUs/gal we get an average total of 53,340 BTUs/gal for the entire production process. [3]
Yes. If we sum the energy needed for production of corn and ethanol conversion and distribution processes we end up with a total expenditure of 68,206BTUs/gal. A gallon of ethanol contains 76,300BTUs/gal and we therefore get an energy ratio of 1.12. This number could be even higher if we incorporated co-products, for example the heat energy that is used during the steam process used during corn conversion, or accounted for the other 34% of the corn that is not used. Some sources have energy ratios reach as high as 1.67. [3]
© Lucy Dikeou. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D. Lorenz and D. Morris, "How Much Energy Does It Take to Make a Gallon of Ethanol?" Institute for Local Self-Reliance, August 1995.
[2] "2008 Energy Balance for the Corn-Ethanol Industry," U.S. Department of Agriculture, Agricultural Economic Report No. 846, June 2010.
[3] "Net Energy Balance of Ethanol Production," Ethanol Across America, March 2009.
