THE NET ENERGY BALANCE OF CORN ETHANOL

Roger ConwayOffice of Energy Policy and New Uses/USDA

The Intersection of Energy and Agriculture:Implications of Biofuels and the Search for a Fuel

of the FutureThe Faculty Club

University of California, BerkeleyOctober 4-5, 2007

Comparison of the Pimental and Patzek results to the USDA resultsProcess Pimentel and Patzek [2] USDA [3] Difference

Btu per Gallon of Ethanol

Corn Production 37,860 18,713 -19,147

Corn Transportation 4,834 2,120 -2,714

Ethanol Conversion 56,399 51,220 -5,179

Energy Input Excluding Coproducts

99,093 72,053 -27,040

Coproduct Value 6,680 26,250 19,570

Energy Input Including Coproducts

92,413 45,803 -46,610

Total Energy Output 77,011 76,330 -681

Net Energy Balance -15,402 30,527 45,929

[1] The study by Shapouri and McAloon, “The 2001 Net Energy Balance of Corn-Ethanol” is available at the USDA, Office of Energy Policy and New Uses web site:

http://www.usda.gov/oce/oepnu/. The Wang study can be found at the following web site: http://www.transportation.anl.gov/research/systems_analysis/fuel_ethanol.html.

[2] Pimentel and Patzek report their results (Table 2 of their paper) in kcal x 1000 per 1000 litres of ethanol. Converted to Btu per gallon using 1 litre = 0.26 gallons and 1

kcal = 3.96 Btu.

[3] Estimates are based on a weighted average of dry and wet milling. Ethanol conversion includes 1,588 Btu per gallon for ethanol distribution.

Net Energy Balance of Corn-Ethanol and 9-State Average Corn Yield per Acre

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Net Energy Balance Results

• Data quality

• Feedstocks, grains, sugar, biomass materials

• New technologies:– Crop production– Processing

• Methodology used to allocate total energy to ethanol and by products

Sources of Data

• USDA/ Economic Research Service (ERS), 2001 Agricultural Resources Management Survey (ARMS)

• USDA/ National Agricultural Statistics Service (NASS), 2001 Agricultural Chemical Usage and 2001 Crop Production

• Stokes Engineering Company, energy used in production of fertilizers

Sources of Data--Continued

• Greenhouse Gas Regulated Emissions and Energy Use in Transportation (GREET) model, energy used in production of chemicals

• 2001 survey of ethanol plants, BBI International, thermal and electrical energy used in ethanol plant

• ASPEN Plus, a process simulation program, to allocate energy used in ethanol plant to ethanol and byproducts

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Energy inputs used per acre of corn, 2001

Pimentel, 2005 USDA/U.S. ave.

Labor, hours 4.62 1.88

Diesel, gallons 9.41 6.2

Gasoline, gal. 4.28 1.7

Nitrogen, lbs 136.28 122

Phosphate, lbs 57.89 34.8

Potash, lbs 68.58 36.21

Lime, lbs 997.57 393

Herbicides, lbs 5.52 2.18

Insecticides, lbs 2.49 0.04

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Fuel Use per Acre of Corn, 2001

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Fertilizer and Lime use per acre of Corn

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Pesticides Use per Acre of Corn, 2001

Pimentel USDA

Comparison of Amount of Energy Used to Produce Corn

Input

Pimentel and Patzek[1] USDA Difference

Btu per Gallon of Ethanol from Corn Production

Labor 2,155 0 -2,155

Machinery 4,749 0 -4,749

Diesel 4,679 2,816 -1,864

Gasoline 1,890 1,323 -567

Nitrogen 11,421 8,824 -2,597

Phosphorus 1,260 613 -647

Potassium 1,171 714 -457

Lime 1,470 24 -1,446

Seeds 2,426 227 -2,199

Irrigation 1,493 62 -1,431

Herbicides 2,893 1,105 -1,787

Insecticides 1,306 -- -1,306

Electricity 159 849 690

Transport 788 76 -713

LP Gas 792 792

Natural Gas 694 694

Custom Work 594 594

Total 37,860 18,713 -19,147

[1] The amount of Btu per gallon of ethanol for each corn input is calculated by taking the share of energy used to produce corn (Table 1 in Pimentel and Pazek) and applying that share to the total amount of energy from corn in ethanol production (Table 2 in Pimentel and Pazek).

New Technologies

• Crop Production:– Genetically modified crops, yield map, global

positioning system, slow release fertilizer, and more efficient irrigation system

• Ethanol plants:– Heat exchanger, heat tolerance yeast, Molecular

sieves, cold cook, dry fractionation, new enzymes, process automation, Combined heat and power, and nano filtration

Corn: Harvested Area and Yield per Acre, 1965-04

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Bushels of Corn per Pound of Pesticides, 1991-03

Dry-Mill: Thermal Energy Use per Gallon of Ethanol and Ethanol Yield per Bushel

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How to Allocate Total Energy to Ethanol and Byproducts

• Methodology:– Energy content– Market value– Output weight basis– Replacement value– Process energy for energy used in plant and %

weight of starch and non-starch for energy used to grow corn and transport corn to ethanol plant

Allocation Rules

• Energy used in corn production:– 66% to ethanol and 34% to byproducts

• Energy used in transporting corn to ethanol plant:– 66% to ethanol and 34% to byproducts

• Energy used in conversion of corn to ethanol and byproducts, ASPEN Plus:– Wet mill, 64% to ethanol and 36% to byproducts

– Dry mill, 59% to ethanol and 41% to byproducts

Conclusions

• Corn yield per acre will continue to increase• Fertilizer industry has become more energy efficient• Energy used to produce a bushel of corn will

continue to decline• Ethanol yield per bushel of corn will increase to its

theoretical limit• Ethanol plants will become more energy efficient• Net energy value of corn-ethanol will continue to

improve