THE NET ENERGY BALANCE OF CORN ETHANOL
Roger Conway Office of Energy Policy and New Uses/USDA
The Intersection of Energy and Agriculture: Implications of Biofuels and the Search for a Fuel of the Future The Faculty Club University of California, Berkeley
October 4-5, 2007
Comparison of the Pimental and Patzek results to the USDA results
Process Pimentel and Patzek [2] USDA [3] Btu per Gallon of Ethanol Corn Production Corn Transportation Ethanol Conversion Energy Input Excluding Coproducts 37,860 4,834 56,399 99,093 18,713 2,120 51,220 72,053 -19,147 -2,714 -5,179 -27,040 Difference
Coproduct Value Energy Input Including Coproducts
6,680 92,413
26,250 45,803
19,570 -46,610
Total Energy Output Net Energy Balance
77,011 -15,402
76,330 30,527
-681 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 9State Average Corn Yield per Acre
180 200 180 160 140 120 100 80 80 60 40 60 40 20 0 1990-92 1995-97 Corn yield 2000-02 Net energy value 2004 160
140 120
Bushels per acre
20
0
Percent
100
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
Sample Size, the 2001 ARMS Corn Survey
3000
2500
2000
Number 1500
1000
500
0 CO GA IL IN IA KS Ky MI MN MN NE NY NC ND OH PA SD TX WI US
Energy inputs used per acre of corn, 2001
Pimentel, 2005 Labor, hours Diesel, gallons Gasoline, gal. Nitrogen, lbs Phosphate, lbs Potash, lbs Lime, lbs Herbicides, lbs 4.62 9.41 4.28 136.28 57.89 68.58 997.57 5.52 USDA/U.S. ave. 1.88 6.2 1.7 122 34.8 36.21 393 2.18 0.04
Insecticides, lbs 2.49
Labor Use per Acre of Corn, 2001
5.00 4.50 4.00 3.50 3.00 Hours 2.50 2.00 1.50 1.00 0.50 0.00 Pimentel USDA
Fuel Use per Acre of Corn, 2001
10.00 9.00 8.00 7.00 6.00 Gallons 5.00 4.00 3.00 2.00 1.00 0.00 Diesel fuel Pimentel USDA Gasoline
Fertilizer and Lime use per acre of Corn
1000 900 800 700 600 Pounds per acre 500 400 300 200 100 0 Nitrogen Phosphate Potash Lime
USDA, 2001
Pimentel
Pesticides Use per Acre of Corn, 2001
6.00
5.00
4.00
Pounds 3.00
2.00
1.00
0.00 Herbicides Pimentel USDA Insecticides
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 Machinery Diesel Gasoline Nitrogen Phosphorus Potassium Lime Seeds Irrigation Herbicides Insecticides Electricity Transport LP Gas Natural Gas Custom Work Total 37,860 2,155 4,749 4,679 1,890 11,421 1,260 1,171 1,470 2,426 1,493 2,893 1,306 159 788 0 0 2,816 1,323 8,824 613 714 24 227 62 1,105 -849 76 792 694 594 18,713 -2,155 -4,749 -1,864 -567 -2,597 -647 -457 -1,446 -2,199 -1,431 -1,787 -1,306 690 -713 792 694 594 -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
80 180 160 140 120 100 40 80 30 60 20 40 20 0 1965 1970 1975 1980 1985 Harvested yield 1990 1995 2000 70
60
10
0
Bushels per acre
50
Million acres
Bushels of Corn per Pound of Fertilizer, 1966-03
0.700 0.600
0.500
0.400
Bushels
0.300
0.200
0.100
0.000 1969 1974 1979 1984 1989 1994 1999
Bushels of Corn per Pound of Pesticides, 1991-03
70 60
50
40 Bushels 30
20
10
0 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Dry-Mill: Thermal Energy Use per Gallon of Ethanol and Ethanol Yield per Bushel
120000 3
100000
2.5
80000
2
60000
1.5
40000
1
20000
0.5
0 1975 1995 2001 Dry mill 2002 Gallon per bushel 2004
0
Gallons per bushel
BTU
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