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Biomass Utilization, Limits of 163

TABLE III Energy Inputs and Costs of Corn Production per quired to produce 1000 l of ethanol than the energy that
Hectare in the United States actually is in the ethanol (Table IV).
Inputs Quantity kcal ×× 1000 Costs In the distillation process, large amounts of fossil en-
ergy are required to remove the 8% ethanol out of the
Labor 11.4 hr 561 $100.00 92% water. For example, to obtain 1000 l of pure ethanol
Machinery 55 kg 1,018 103.21 with an 8% ethanol concentration out of 92% water, then
Diesel 42.2 L 481 8.87 this ethanol must come from the 12,500 l of ethanol/water
Gasoline 32.4 L 328 9.40 mixture. A total of 124 l of water must be eliminated per
Nitrogen 144.6 kg 2,668 89.65 liter of ethanol produced. Although ethanol boils at about
Phosphorus 62.8 kg 260 34.54 78 C, in contrast to water at 100 C, the ethanol is not ex-
◦
◦
Potassium 54.9 kg 179 17.02 tracted from the water in one distillation process. Instead,
Lime 699 kg 220 139.80 about 3 distillations are required to obtain the 95% pure
Seeds 21 kg 520 74.81 ethanol that can be mixed with gasoline. To be mixed with
Herbicides 3.2 kg 320 64.00 gasoline, the 95% ethanol must be further processed with
Insecticides 0.92 kg 92 18.40 more energy inputs to achieve 99.8% pure ethanol. The
Irrigation 150 mm 3,072 150.00 three distillations account for the large quantities of fos-
Electricity 13.2 kg 34 2.38 sil energy that are required in the fermentation/distillation
Transportation 151 kg 125 45.30 process. Note, in this analysis all the added energy inputs
Total 10,439 $857.17 for fermentation/distillation process are included, not just
Corn yield 27,758
the fuel for the distillation process itself.
= 7,965 kg kcal output/kcal input = 1 : 2.66
This contrasts with Shapouri et al. who, in 1995, give
only one figure for the fermentation/distillation process
From Pimentel, D., Doughty, R., Carothers, C., Lamberson, S., Bora,
N., and Lee, K. J. Agr. Environ. Ethics (in press). and do not state what the 3.4 million kilocalories repre-
sents in their analysis for producing 1000 l of ethanol.
Careful and detailed analyses and full accountings are
pumped from only 30.5 m (100 feet), the average energy needed to ascertain the practicality of ethanol production
input is 3.1 million kilocalories/hectare (Table III). as a viable energy alternative.
When investigators ignore some of the energy inputs About 61% of the cost of producing ethanol (46c / per
in biomass production and processing they reach an in- liter) in such a large-production plant is for the corn sub-
complete and deficient analysis for ethanol production. In strate itself (28c / /l) (Table IV). The next largest input is for
a recent USDA report, no energy inputs were listed for coal to fuel the fermentation/distillation process, but this
machinery, irrigation, or for transportation. All of these was only 4c / (Table IV). These ethanol production costs
are major energy input costs in United States corn pro- include a small charge for pollution control (6c / per liter),
duction (Table III). Another way of reducing the energy which is probably a low estimate. In smaller plants with
inputs for ethanol production is to arbitrarily select lower an annual production of 150,000 l/yr, the cost per liter in-
production costs for the inputs. For instance, Shapouri creases to as much as 66c / per liter. Overall, the per liter
et al. list the cost of a kilogram of nitrogen production at
12,000 kcal/kg, considerably lower than Food and Agri-
cultural Organization of the UN (FAO), which list the cost TABLE IV Inputs per 1000 l of Ethanol Produced from Corn
of nitrogen production at 18,590 kcal/kg. Using the lower Inputs Kilograms Kilocalories (1000) Dollars
figure reduces the energy inputs in corn production by
about 50%. Other workers have used a similar approach Corn 2,600 3,408 $280
to that of Shapouri et al. Transport of corn 2,600 312 32
The average costs in terms of energy and dollars for a Water 160,000 90 20
large (240 to 280 million liters per year), modern ethanol Stainless steel 6 89 10
plant are listed in Table IV. Note the largest energy in- Steel 12 139 10
puts are for corn production and for the fuel energy used Cement 32 60 10
in the fermentation/distillation process. The total energy Coal 660 4,617 40
input to produce 1000 l of ethanol is 8.7 million kilocalo- Pollution control costs — — 60
ries (Table IV). However, 1000 l of ethanol has an energy Total 8,715 $462
value of only 5.1 million kilocalories. Thus, there is a net From Pimentel, D., Warneke, A. F., Teel, W. S., Schwab, K. A.,
energy loss of 3.6 million kilocalories per 1000 l of ethanol Simcox, N. J., Ebert, D. M., Baenisch, K. D., and Aaron, M. R., (1988).
produced. Put another way, about 70% more energy is re- Adv. Food. Res. 32, 185–238.