COMMENT: Analysis highlights limits on energy promise of biofuels

Feb. 5, 2007
According to environmentalists and a growing array of politicians, biofuels are going to dramatically reduce our dependence on foreign oil supplies, replace dirty fossil energy with “clean” renewable energy, and sharply reduce carbon emissions.

According to environmentalists and a growing array of politicians, biofuels are going to dramatically reduce our dependence on foreign oil supplies, replace dirty fossil energy with “clean” renewable energy, and sharply reduce carbon emissions. The facts are rather different.

In part because the ethanol industry is already well developed, the promoters of biofuels have focused their attention on ethanol to power the transportation sector. On Dec. 27, 2006, the Governors’ Ethanol Coalition, which consists of the governors of 37 states, sent a letter to Congress in which they asked Congress to require that 15% of motor fuels consumption on a btu basis consist of ethanol and biodiesel by 2015.1 2

Analysis of the goal expressed by the coalition helps put into perspective the even more-ambitious targets outlined recently in Congress and in the state-of-the-union address Jan. 23 by President George W. Bush.

Consumption, population

Per-capita gasoline consumption in 2005 was 11.2 bbl-the same as in 1974.3 Although the average fuel economy of passenger cars on the road increased from 13.6 mpg to 22.4 mpg, this improvement in fuel economy was offset by increases in the number of vehicles and the mileage each vehicle was driven.4

If current trends in immigration and population growth remain intact, the US population will reach about 330.5 million in the year 2015.5 If per-capita gasoline consumption remains constant, US gasoline demand in 2015 will reach 3.72 billion bbl, or about 19.1 quadrillion btu.

Although ethanol can be made from a variety of cellulosic materials, such as straw, virtually all of the ethanol produced in the US today is made from corn, and there is little reason to believe this situation will change in the near future. Replacing 15% of this gasoline demand with ethanol derived from corn would consume 13.6 billion bushels of corn, or 130% of the US corn crop.6 About 94 million acres of prime farm land would have to be devoted to corn production just for fuel ethanol. These people need a reality check.

In 2005, about 14% of the US corn crop went into ethanol production, and this has caused a sharp increase in corn prices.7 On Jan. 22, the March 2007 contract price was $4.04/bushel. A year earlier, the March 2006 contract price was $2.08/bushel. Rising corn prices are already affecting both poultry and beef producers, and rising retail meat prices are expected soon.7

Water requirements

It is worth noting that approximately 14% of the US corn crop is irrigated and that this irrigated acreage consumes almost 18 million acre-ft/year of water-much of which is overdrafted from the Ogallala aquifer in the Great Plains.8 9 To put this water requirement into some perspective, the average annual flow of the Colorado River at Lee’s Ferry, Ariz., is only about 14 million acre-ft. Furthermore, much of this corn acreage in the Great Plains states is easily erodible land, and numerous studies have conclusively demonstrated that row crops, such as corn, result in much higher erosion rates than cereal grains or forage crops. In one such study, done near Zanesville, Ohio, a continuous corn cropping sequence produced a soil loss nine times that for wheat grown in a rotation sequence with corn.10

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The potential for expanding corn acreage is limited, and the potential for expanding corn acreage without causing significant environmental damage is even more limited. Harvested acreage, production, and yield date for the major field crops in the US are shown in Table 1.11 The data shown are averages for the 4-year period 2002-05.12 The various categories of cropland in the US are shown in Table 2.13

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Of the 40 million acres of idle cropland shown in the table, about 35 million acres are enrolled in the Conservation Reserve Program (CRP).14 The CRP was originally authorized by Congress in 1985 for the purpose of protecting erodible land from erosion. Under this program, owners of highly erodible land are paid a per-acre fee by the US Department of Agriculture (USDA) for taking such land out of crop production for a 10-year period and planting a cover crop, such as grass, to reduce soil erosion. About 13.6 million acres of land enrolled in the CRP were converted from wheat in the six states: North Dakota, South Dakota, Montana, Wyoming, Colorado, and Kansas.14 Without irrigation, this land is too arid for corn production. Because corn generates almost twice the per-acre revenue as wheat, farmers with good soil and adequate rainfall will almost always choose to grow corn rather than wheat. Therefore, most of the 50 million acres of wheat acreage is not suitable for corn production.

As the data in Table 1 show, the big four field crops-corn, soybeans, wheat, and hay-account for three fourths of US cropland used for crops. The only real potential for expanding corn production is at the expense of soybean acreage, since soybeans and corn are often grown in rotation sequence to take advantage of the ability of soybeans to sequester nitrogen in the soil. This rotation reduces natural gas-derived nitrogen fertilizer requirements for the subsequent corn crop. In addition, of course, the soybean meal residual after crushing the beans for oil is used extensively as a high-protein supplement in animal feeds.

A.E. Farrell and colleagues of the Energy Resources Group at the University of California, Berkeley, recently published the results of a study to determine the net energy balance of fuel ethanol.15 In the course of that work, which concluded that the net energy balance is positive, the authors found that the renewable-energy (solar) content of corn ethanol was only 5-26%. The balance of the energy input is primarily natural gas and coal. Let’s assume the average is 16%. If 15% of the year 2015 gasoline supply is ethanol, then the renewable content of this gasoline is only 0.46 quads, or 2.4%. Worse, this entire renewable contribution will be offset by a population-driven increase in gasoline demand within 3 years.

Biodiesel limits

Although the Governors’ Ethanol Coalition report focused largely on corn ethanol, it did include some recommendations on biodiesel. Recently, a number of articles have also appeared in the popular press touting the supposed benefits of biodiesel fuel as a substitute for conventional diesel. However, none of these have addressed the question of potential production of biodiesel.

Biodiesel fuel is produced from fats and oils, but these fats and oils are also consumed in food, animal feed, and chemical production. The only oils that currently can be considered surplus and available for biodiesel production are those that are exported. These exported oils-primarily oilseed oils, such as soybean-could produce about 40 million bbl/year of biodiesel, or about 0.5% of US petroleum consumption.16

In order to increase the supply of oils for biodiesel production, the acreage of oilseeds (mostly soybeans or canola) would have to be expanded. The top five soybean-producing states-Iowa, Illinois, Minnesota, Indiana, and Nebraska-are also the top five corn-producing states. Consequently, soybean acreage is in competition with corn acreage for ethanol production, and, indeed, soybean acreage in the top seven producing states declined between 2001 and 2005.17 Since soybeans require a warm, humid climate, they are not grown in the arid West, even with irrigation. Consequently, the potential for expansion of soybean acreage is limited.

It has been suggested that some CRP land might be planted to canola when the CRP contracts expire. Of the 34.8 million acres currently under CRP contracts, 13.3 million acres, or almost 40% of the total, are in North Dakota, South Dakota, Montana, Kansas, and Colorado.14 If all 13.3 million acres were planted in canola, 23 million bbl/year of biodiesel could be produced.18 19 This amounts to just 0.3% of current US petroleum consumption.

It is worth noting that any conversion of CRP land back to crop production would have serious erosion implications. On a silt-loam soil with 12% slope in Ohio, the soil loss from a field of wheat was 57 times the soil loss from a field of second-year grass. The soil loss from a field seeded with canola would almost certainly be greater than from wheat, and CRP land is, by definition, highly erodible. Growing a crop that results in a fifty-sevenfold increase in soil erosion to produce a minuscule fraction of the US petroleum supply hardly qualifies as environmentally beneficial or sustainable.

Biofuels, energy

As the gasoline data show, biofuels simply cannot provide either the liquid fuels or the total energy required by the US economy. Indeed, even if it were possible to collect all of the aboveground residue from the 200 million acres of corn, soybeans, wheat, oats, and rice in the US, the energy content of that residue is only about 7.4 quads, or about 7.4% of US primary energy consumption. Table 3 shows data used in this calculation.

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Note that the 7.4 quads is the total gross energy content of the residues. The net energy available after collection, processing, and replenishment of nutrients removed with the residue would be considerably less.

It is time for politicians to stop pretending that biomass can make any significant contribution to US energy supplies or reduction of carbon emissions.


  1. Seblius, Kathleen, Heineman, Dave, letter to the Congressional Leadership, Governors’ Ethanol Coalition, Dec. 27, 2006.
  2. “Ethanol from Biomass: How to Get a Biofuels Future,” Governors Ethanol Coalition, December 2006.
  3. Gasoline consumption data for 1974 taken from Table 3.4, “Finished Motor Gasoline Supply, Disposition and Stocks,” Monthly Energy Review, May 2005, DOE/EIA-0035(2005/05). Data for 2005 taken from Table 3.4, “Finished Motor Gasoline Supply, Disposition, and Stocks, Monthly Energy Review,” July 2006, DOE/EIA-0035(2006/07). Population data for 1974 taken from Table 2, Population 1960-2002, US Statistical Abstract, US Census Bureau. Population data for 2005 taken from Table 1, Annual Estimates of the Population of the US and Puerto Rico: Apr. 1, 2000-July 1, 2005, [NST-EST 2005-01], Dec. 22, 2005.
  4. Table 1.9, Motor Vehicle Mileage, Fuel Consumption, and Fuel Rates, Monthly Energy Review, July 2006, DOE/EIA-0035(2006/07).
  5. Computed using a natural rate of increase of 0.565%/year, the average for the period 1999-2004, and immigration data from S.2611, Comprehensive Immigration Reform Act of 2006, Congressional Budget Office Cost Estimate, US Congressional Budget Office, Washington, DC, Aug. 18, 2006.
  6. The following heat values used in this calculation were taken from Table A1, Approximate Heat Content of Petroleum Products, Monthly Energy Review, July 2006, DOE/EIA-0035(2006/07): Reformulated gasoline = 5.150 million btu/bbl; Fuel ethanol = 3.539 million btu/bbl. Ethanol yield from corn is approximately 2.5 gal/bushel. During the 4-year period 2002-05, the average annual harvested acreage of corn in the US was 72.253 million acres, and annual production averaged 10.494 billion bushels. Data obtained from: US and All States Data for Crops-Planted, Harvested, Yield, Production, Price, and Value of Production, NASS-USDA-Quick Stats-Crops, National Agricultural Statistics Service, US Department of Agriculture, 2006.
  7. Fialka, J.J., “Ethanol Bandwagon Picks Up Speed,” Wall Street Journal, Jan. 10, 2007, p. A2.
  8. Irrigated acreage for corn from County Data for Crops-Corn, USDA-NASS-Quick Stats-Crops, National Agricultural Statistics Service, US Department of Agriculture, 2006.
  9. Consumptive irrigation water requirement for corn taken as 24.2 in./year from Facts and Figures, Westlands Water District, Fresno, Calif., 1989. Since Westlands Water District is one of the most efficient irrigation districts in the country, actual water use by US farmers growing irrigated corn will be greater.
  10. Zublena, J.P., Corn Cropping Sequences, NCH-50, National Corn Handbook, Purdue University Cooperative Extension Service, West Lafayette, Ind., 1987.
  1. Data taken from Crop Production, 2005 Summary, National Agricultural Statistics Service, USDA, January 2006; Crop Production, 2003 Summary, National Agricultural Statistics Service USDA, January 2004.
  2. Since both harvested acreage and crop yields fluctuate in response to climatic and economic factors, we have calculated averages for the 4-year period 2002-05. Because corn acreage has been increasing and soybean acreage has been declining in response to ethanol production, calculating averages over a longer time frame appeared unwise.
  3. Lubowski, R.N., Vesterby, M., Bucholtz, S., Baez, A., Roberts, M.J., “Major Uses of Land in the United States, 2002,” 2002/EIB-14, Economic Research Service USDA, 2006.
  4. Table 12-13, Conservation Reserve Program: Enrollment by State, January 2005, Agricultural Statistics 2005, National Agricultural Statistics Service, USDA, 2006.
  5. Farrell, A.E., Plevin, R.J., Turner, B.T., Jones, A.D., O’Hare, M., Kammen, D.M., “Ethanol Can Contribute to Energy and Environmental Goals,” Science 311, No. 5760, Jan. 27, 2006, pp. 506-508.
  6. Tyson, K.S., Bozell, J., Wallace, R., Petersen, E., Moens, L., “Biomass Oil Analysis: Research Needs and Recommendations,” NREL/TP-510-34796, National Renewable Energy Laboratory, Golden, Colo., June 2004.
  7. State Data-Soybeans-Planted, Harvested, Yield, Production, Price, Value of Production, NASS-Quick Stats-Crops, National Agricultural Statistics Service, US Department of Agriculture, 2006.
  8. In calculating this we used a yield of 1,405 lb/acre for canola (the average for the period 2001-05), obtained from reference 19 and 0.0513 gal biodiesel/lb of canola obtained from reference 16.
  9. National Statistics: Canola-Planted, Harvested, Yield, Production, Value of Production, NASS-USDA-Quick Stats, National Agricultural Statistics Service, USDA, 2006.

The author

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Donald F. Anthrop is professor emeritus of environmental studies at San Jose State University, San Jose, Calif., where he taught for 34 years. He earned his doctorate in materials engineering at the University of California, Berkeley, and is the author of over 70 papers on energy and water resources, including a pioneering work published in the Bulletin of Atomic Scientists in 1970 entitled, “The Environmental Side Effects of Energy Production.” He currently resides in Berkeley and can be reached at [email protected].