Ethanol fuel in the United States
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(This is a subsidiary of the Ethanol fuel article.)
Ethanol energy balance in the United States
The total energy needed to produce ethanol from corn grain — including fermentation, fertilizing, fuel for farm tractors, harvesting and transporting the grain, building and operating an ethanol plant, and the natural gas used to distill corn sugars into alcohol — is about the same (within a factor of two plus or minus) as the energy content of the ethanol produced. Most studies have concluded that ethanol production yields more energy than it consumes, in a ratio of about 1.34:1, or that corn ethanol yields 26% more energy than is used to make it. [link] and see below).
Studies by Cornell University ecology professor David Pimentel and Tad Patzek of the University of California-Berkeley have concluded that the use of corn ethanol for fuel would have a negative net energy balance. Pimentel's study was disputed by a number of researchers, forcing him to revise his figures. Still, in August 2003 (and again in March 2005), he stated in a Cornell bulletin that production of ethanol from corn takes 29% more energy than it produces, ethanol from switch grass requires 45% more energy and ethanol from wood biomass requires 57% more energy that it produces [link].
Using old data biases the outcome in these studies. According to the USDA, farms have become more energy efficient since 1978 due in large part to replacing gasoline powered equipment with more fuel-efficient diesel engines. Total farm energy use peaked in 1978 at 2,244 trillion Btu (2.368 EJ), but by 2000 had dropped to about 1,600 trillion Btu (1.7 EJ). In the meantime, corn production rose from an average of 110 bushels per acre (6.9 Mg/ha) in 1980 to 140 bushels per acre (8.8 Mg/ha) in 2000.
Pimentel concluded that the yield was 218 US gallons per acre (204 m³/km²) of gasoline equivalent, due to the energy in ethanol being only 66% that of gasoline. Pimentel also calculated that corn (maize) production requires about 115 US gallons per acre (108 m³/km²) of gasoline equivalent. Thus, he calculated a net energy production of 103 US gallons per acre (96 m³/km²), while his studies somehow all concluded a net energy loss in producing ethanol. Critics of Pimentel's study cite questionable deductions, for example; 1,000,000 Btu per acre (260 kJ/m²) for labor, 5,656,000 Btu per acre (1474 kJ/m²) for machinery, as well as additional deductions for steel and concrete production and construction of ethanol refineries, while not saying from where these numbers were derived. (Shapouri, Hosein, James A. Duffield, Michael Wang. The Energy Balance of Corn Ethanol: An Update. USDA: Office of the Chief Economist; Office of Energy Policy and New Uses. Washington, DC. July, 2002) Although ethanol does have 66% of the energy per unit of volume of gasoline, its higher octane rating enables higher compression and therefore higher efficiency engines.
The focus of the USDA report, and others, was on ethanol and the energy balance equation, but according to a report by the Minnesota Department of Agriculture, when taking into account the energy needed to extract, transport and refine crude oil into gasoline, the final energy product of gasoline has an energy ratio of 0.805. That means that about 20% of the total theoretical energy content of crude oil is consumed/lost in the process of gasoline production. (Groschen [link]) The ratio of energy produced to energy consumed in gasoline production is generally about 15-20:1 currently, and may have been over 100:1 previously, when using the most easily-accessed crude oil.
Continual refinements to ethanol production procedures (including steady gains in agricultural productivity) advance the ethanol the benefit/cost ratio, and most studies of modern systems indicate that they now have a positive net energy balance. Also, when ethanol is mixed with water vapor and converted into hydrogen, it does not need to be as pure as when it is used in a combustion engine, making the process more efficient. (see source below)
Many other studies of corn ethanol production have been conducted, with greatly varied net energy estimates. Most indicate that production requires energy equivalent to 1/2, 2/3, or more of the fuel produced to run the process. A 2002 report by the United States Department of Agriculture concluded that corn ethanol production in the U.S. has a net energy value of 1.34, meaning 34% more energy was produced than what went in. This means that 75% (1/1.34) of each unit produced is required to replace the energy used in production. The study also concluded that the energy used to produce and convert the ethanol was from abundant domestic sources, with only 17% of the energy used coming from liquid fuels, therefore, for every 1 unit of energy from liquid fuel used, such as gasoline or diesel fuel, there was a gain of 6.34 units of energy. [MSU Ethanol Energy Balance Study:] Michigan State University, May 2002. This comprehensive, independent study funded by MSU shows that corn ethanol production has a net energy value of 1.56: it produces 56% more energy per unit volume of ethanol than it consumes. Nevertheless, as noted earlier, these relatively small energy gains are problematic, for they imply that between 2.79 (assuming net energy value 1.56) and 3.94 (assuming net energy value 1.34) units of ethanol must be produced for each unit of ethanol that can be sold to consumers. Actual net energy values might be improved by measures such as burning corn stalks (which are not fermentable using current technology) to run some parts of the corn ethanol production process that currently consume petroleum, gas, or ethanol (similarly to the way bagasse is currently burned to produce energy to run the ethanol production facilities in Brazil). As of 2005, ethanol production from corn may require an increase in the cost of petroleum before becoming economically viable without government subsidies. Although for periods in the year 2005 ethanol traded for less than gasoline and diesel before any subsidy.
A 2005 study by [Michael Wang], a transportation research scientist at the US Department of Energy Argonne National Laboratory, found that "the energy used for each unit of ethanol produced has been reduced by about half [since 1980]." Now, it takes 0.74 million BTU of fossil fuels to deliver 1 million BTU of ethanol, including growing, all intermediary processes, delivery, and so on, compared to 1.23 million BTU of fossil fuels to deliver 1 million BTU of gasoline. This more recent study may obsolete some of the previous criticisms of the ethanol energy balance, as the production, transportation, and storage has become much more efficient. [link] [link] [link]
External links
- [corn and other crops is not worth the energy]
- [Pimentel: Ethanol - Inefficient Fuel] and [Debunking Pimentel: Ethanol - Efficient Fuel]
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