COMMENT: US exaggerating hope for renewable energy

July 27, 2009
Far from learning any lessons from their ill-conceived foray into biofuels through the Energy Independence and Security Act of 2007 (EISA), Congress and the Obama administration appear destined to compound their mistakes in the huge climate bill now making its way through Congress.

Far from learning any lessons from their ill-conceived foray into biofuels through the Energy Independence and Security Act of 2007 (EISA), Congress and the Obama administration appear destined to compound their mistakes in the huge climate bill now making its way through Congress. The House version of this bill would require that renewable energy sources account for 20% of US electrical production by 2020. President Barack Obama, both during the campaign and in office, has asked that 25% be derived from renewable sources by 2025.

Because of the potential for more government mandates, some electrical utilities are planning to build power plants fueled with biomass. The Energy Information Administration (EIA) is forecasting 230 billion kw-hr of electrical energy from biomass by 2030.1 This amounts to about 5.6% of 2008 US electrical energy generation (4,110 billion kw-hr).2

Government policy-makers would like us to believe there are vast quantities of crops, crop residues, and unused wood waste that can be easily converted into energy. The facts are quite different.

Let’s start with the renewable fuel standard (RFS) that the Environmental Protection Agency proposed on May 6. The EISA mandates the use of 36 billion gal/year of biofuels by 2022. It also caps ethanol derived from corn starch at 15 billion gal. The RFS proposed by EPA requires the use of 16 billion gal of cellulosic ethanol (i.e., ethanol derived from the cellulose in plant material) and at least 1 billion gal of biodiesel. At present, 4 billion gal of biofuel remains unspecified, but EPA may require up to 5 billion gal of biodiesel after 2012.3 4 5

Corn ethanol

Let’s first look at ethanol derived from corn starch. Production of 15 billion gal of ethanol, the yield for which is about 2.4 gal/bushel of corn, would consume 6 billion bushels of corn, or half of last year’s corn crop of 12.1 billion bushels from 71.6 million harvested acres.6 The area of cropland needed to produce 15 billion gal of ethanol is 39 million acres.

About 14% of US corn production comes from irrigated land, almost all of which is irrigated with groundwater that is overdrafted from the Ogallala aquifer. Last year, an area of about 9.5 million acres of corn land was irrigated, of which about 8.9 million acres was irrigated with groundwater from the Ogallala aquifer.7 This irrigated acreage consumed some 18 million acre-feet of groundwater.8 To put this in perspective, the average annual flow of the Colorado River at Lee’s Ferry, Ariz., is only about 14 million acre-ft.

If the US were able to produce 15 billion gal/year of ethanol from corn starch, how much gasoline would this ethanol displace? The answer is about 7.5% of year 2008 gasoline consumption, estimated by the EIA in its Monthly Energy Review of May 2009 at 8.964 million b/d. This calculation uses approximate heat values from the same source of 5.150 million btu/bbl of reformulated gasoline and 3.539 million btu/bbl of fuel ethanol.

A policy that requires dedication of 39 million acres of prime cropland to produce a crop, one seventh of which is grown with overdrafted groundwater, in order to replace 7.5% of US gasoline supply hardly qualifies as environmentally sustainable and surely does little to achieve energy independence, especially since the renewable energy content of corn ethanol has been found to be only 5-26%.9 The balance of the energy input to corn ethanol is primarily natural gas and coal.

Cellulosic ethanol

Even more daunting is the mandate for 16 billion gal of cellulosic ethanol by 2022. There is no commercial production of cellulosic ethanol at present. Even if commercial production is attained, the ability of the industry to expand production to meet these mandates is very uncertain.

More worrisome, however, is the availability of potential feedstocks for cellulosic ethanol. Corn produces the most residue of any crop grown in the US. During the 5-year period 2004-08, when the average corn yield was 152.4 bushels/acre, the average annual residue produced by the US corn crop was 352 million tons.10 This is based on estimated corn residue of 6,000 lb/acre for a grain yield of 100 bushels/acre and 9,000 lb/acre for a grain yield of 150 bushels /acre.11

However, agronomists are becoming increasingly alarmed at the prospect of residue removal for energy production because of the deleterious effects on soils—namely increased erosion; reduced soil organic matter; loss of nutrients, especially phosphorus and potash; and soil compaction.12 13 14 15 Agronomists are advising farmers to remove no more than 30% of corn residues.12 Corn residue yields about 72 gal of ethanol/ton.16 If 30% of the residue were collected from the entire US corn crop, about 7.6 billion gal of ethanol could be produced from the 105 million tons of residue.

In reality, probably only half of the available residue would be collected because of the economics and fuel consumed in transporting it to a processing plant. Four states—Iowa, Illinois, Nebraska, and Minnesota—account for about half of the US corn acreage. To put the residue collection problem in some perspective, collection of half of the available residue in the US would be the equivalent of collecting all of the available residue in these four states.

Small grains—wheat, oats, barley, rice—produce much less residue than corn. During 2004-08, wheat produced about 2.1 tons of residue per acre.17 Agronomists have urged farmers to leave at least 1 ton/acre in place for erosion control and soil fertility maintenance.18 19 If the extra 1.1 tons/acre were removed from the entire US wheat acreage (50.7 million acres) and converted to cellulosic ethanol, about 3.8 billion gal of ethanol could be produced. This calculation uses an ethanol yield of 69 gal/ton of straw.19

Data for crop residue, energy content of the residue, and potential ethanol yield from the residue for the major field crops are summarized in Table 1. Heat values for specific residues appear in Table 2.

The data in the table indicate the maximum cellulosic ethanol production from crop residue if all of the available residues, in excess of those needed for erosion protection, were collected is about 12.4 billion gal/year. The total energy content of these residues is only about 2.6% of total annual US energy consumption.

In reality, probably only half of these residues could be economically collected. Soybeans do not produce enough residue to make removal feasible. Hay, the other major crop, produces no field residue. The total acreage of the above crops is 269 million acres—almost 80% of the land in the US that is used for crop production.

Biodiesel

As noted earlier, the RFS proposed by EPA requires the use of at least 1 billion gal of biodiesel by 2022, although the EPA may require use of greater volumes of biodiesel after 2012—possibly up to a total of 5 billion gal.

Virtually all of the biodiesel fuel produced in the US is made from oilseeds, primarily soybeans. Production of 1 billion gal of biodiesel will require 17 million acres of soybeans or 24% of the US soybean crop. This is based on the average soybean yield during 2004-08 of 41.9 bushels/acre and a biodiesel yield of 0.02357 gal/lb.20 21 And how much diesel fuel will these soybeans replace? A miniscule 1.2% of the year 2008 distillate consumption reported by EIA in May!

Since soybeans require a warm, humid climate, they cannot be grown in the West, even with irrigation. Consequently, soybeans and corn compete for the same cropland. Because of the 39 million acres that will be needed for the 15 billion gal of ethanol from corn starch, corn land will not be available for soybean production.

This is an even more ludicrous undertaking than cellulosic ethanol.

Renewable electricity

Now let’s look at the Obama administration’s ill-conceived proposal to require electric utilities to obtain 25% of their electrical energy from renewable sources.

As noted earlier, EIA is forecasting 230 billion kw-hr of electrical energy from biomass in 2030. We have already seen that the US does not produce enough crop residues to meet the RFS mandates even if all of the available residues could be collected. Consequently, utilities are looking at wood as a fuel source for these plants.

The days are long past when lumber mills and wood processors disposed of sawdust and mill waste by burning. Today, these residues are either converted into building products or burned in cogeneration plants on-site, and logging residue—limbs, branches, needles, split logs—is typically left on the forest floor for erosion control and nutrient replenishment.

A modern coal-fired electrical generating plant has an overall conversion efficiency of about 40%. Although it is likely to be lower for a wood-fired plant, let’s assume a conversion efficiency of 40%. The average annual timber growth (all species) on US commercial timberland is 44 cu ft/acre.22 In order to produce 230 billion kw-hr/year of electrical energy, the US would need to dedicate 156 million acres of commercial timberland to fuelwood production. This is based on an average density for softwoods and hardwoods of 39.1 lb/cu ft.23

The US would need to devote 29% of its commercial timberland, which totals 541.1 million acres, to fuelwood production in order to obtain 5.6% of its electrical energy.22 And the environmentalists were complaining about road construction in the national forests under the Bush administration.

The government needs to get out of the energy business before misadventures in biofuels lead to economic and environmental ruin.

References

  1. Annual Energy Outlook 2009, Table A16, Renewable Energy Generating Capacity and Generation, DOE/EIA-0383(2009), March 2009.
  2. Net generation of electrical energy in 2008 was 4,110 billion kw-hrs. Taken from: Electric Power Monthly, June 2009, Table 1.1, Net Generation by Energy Source; Total (All Sectors), DOE/EIA-0226(2009/06), June 12, 2009.
  3. HR 6, Energy Independence and Security Act of 2007, Public Law 110-140, signed Dec. 19, 2007.
  4. “EPA’s Proposed Renewable Fuel Standard Tackles GHG Emissions,” EERE Network News, Energy Efficiency and Renewable Energy Office, US Deptartment of Energy, May 6, 2009.
  5. Yacobucci, B.D., Capehart, T., “Selected Issues Related to an Expansion of the Renewable Fuel Standard [RFS],” Report RL34265, Congressional Research Service, Mar. 31, 2008.
  6. Data from National Statistics—Field Corn, NASS—USDA—Quick Stats—Crops, National Agricultural Statistics Service, US Dept. of Agriculture, 2009.
  7. Irrigated acreage for corn from County Data for Crops—Corn, USDA—NASS—Quick Stats—Crops, National Agricultural Statistics Service, US Dept. of Agriculture, 2009.
  8. Consumptive irrigation water requirement for corn taken as 24.2 in./year from “Facts and Figures,” Westlands Water District, Fresno, Calif., 9189. Since Westlands is one of the most efficient irrigation districts in the country, actual water use by US farmers growing irrigated corn will be greater.
  9. Farrell, A.E., Plevin, R.J., Turner, B.T., O’Hare, M., Kammen, D.H., “Ethanol Can Contribute to Energy and Environmental Goals,” Science 311, No. 5760, Jan. 27, 2006, pp. 506-508.
  10. Data from “National Statistics—Field Corn,” USDA—NASS—Quick Stats—Crops, National Agricultural Statistics Service, US Department of Agriculture, 2009.
  11. Data from “Harvesting Corn Residue,” AGF-003-92, Department of Horticulture and Crop Science, Ohio State University, Columbus, Ohio.
  12. Wilhelm, W.W., Johnson, J.M. F., Hatfield, J.L. Voorhees, W.B., Linden, D.R., “Crop and Soil Productivity Response to Corn Residue Removal: A Literature Review,” Agronomy Journal 96, No. 1, Jan./Feb. 2004, pp. 1-17.
  13. “Biofuels from Corn Residue Need Updated Environmental Protections,” Press release, World Resources Institute, Washington, DC, Jan. 27, 2009.
  14. Marshall, L., Zachary, S., “Corn Stover for Ethanol Production; Potential and Pitfalls,” WRI Policy Note, World Resources Institute, Washington, DC, January 2009.
  15. Van Osdell, M.A., “Wheat Acreage, Yield Down in Louisiana,” Delta Farm Press, Ag Center, Agricultural Extension Service, Louisiana State University, Baton Rouge, Apr. 22, 2009.
  16. Calculated from data given by McLoon et. al, Tech. Rept. NREL/TP-580-28893, National Renewable Energy Lab., Golden, Colo., who report a conversion efficiency of 300 l./1,000 kg stover.
  17. During 2004-08, the average yield for wheat was 41.9 bushels/acre, and the average harvested acreage was 50.7 million acres. Data from National Statistics–Wheat, USDA—NASS—Quick Stats—Crops, National Agricultural Statistics Service, US Department of Agriculture, 2009. Residue calculated using an estimate of 100 lb of residue per bushel of wheat from Hickman, J. S., Schoenberger, D. L., “Estimating Wheat Residue,” Rept. L-781, Cooperative Extension Service, Kansas State University, Manhattan, Kan., May 1989.
  18. Presley, D., “Factors to Consider before Burning Wheat Residue,” Agronomy e-Update, Cooperative Extension Service, Kansas State University, Manhattan, Kan.
  19. “Wheat Straw for Ethanol Production in Washington: A Resource, Technical, and Economic Assessment,” Report WSU CEEP 2001084, Cooperative Extension Service, Washington State University, Pullman, Wash., September 2001.
  20. Average yield of soybeans over 2004-08 was 41.9 bu/ac. Taken from National Statistics—Soybeans, USDA—NASS—Quick Stats—Crops, National Agricultural Statistics Service, US Dept. of Agriculture.
  21. Biodiesel yield = 0.02357 gal/lb soybeans from Tyson, et. al., Biomass Oil Analysis: Research Needs and Recommendations, NREL/TP-510-34796, National Renewable Energy Lab., Golden, CO, June 2004.
  22. Calculated from data in Table 12-19, “Forest Land: Total Forest Land Area and Ownership of Timberland” by regions, Jan. 1, 2002; Table 12-22, “Timber Growth, Removals, and Mortality, 2002,” Agricultural Statistics, 2008, US Department of Agriculture.
  23. Calculated from “Weights of Various Woods,” Simetric Co., UK, 2008.

The author

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].