C 2005)
Natural Resources Research, Vol. 14, No. 1, March 2005 (DOI: 10.1007/s11053-005-4679-8

Ethanol Production Using Corn, Switchgrass, and Wood;
Biodiesel Production Using Soybean and Sunflower
David Pimentel1,3 and Tad W. Patzek2
Received and accepted 30 January 2005

Energy outputs from ethanol produced using corn, switchgrass, and wood biomass were eachless than the respective fossil energy inputs. The same was true for producing biodiesel using soybeans and sunflower, however, the energy cost for producing soybean biodiesel was
only slightly negative compared with ethanol production. Findings in terms of energy outputs
compared with the energy inputs were: • Ethanol production using corn grain required 29%
more fossil energy than the ethanol fuel produced. • Ethanol production using switchgrassrequired 50% more fossil energy than the ethanol fuel produced. • Ethanol production usingwood biomass required 57% more fossil energy than the ethanol fuel produced. • Biodiesel
production using soybean required 27% more fossil energy than the biodiesel fuel produced(Note, the energy yield from soy oil per hectare is far lower than the ethanol yield from corn).
• Biodiesel production using sunflower required 118% more fossil energy than the biodiesel
fuel produced.
KEY WORDS: Energy, biomass, fuel, natural resources, ethanol, biodiesel.

INTRODUCTION

unanimously approved. Numerous other investigations have confirmed these findings over the past two
decades.
A review of the reports that indicate that corn
ethanol production provides a positive return indicates that many inputs were omitted (Pimentel, 2003).
It is disappointing that many of the inputs were omitted because this misleads U.S. policy makers and the
public.
Ethanol production using corn, switchgrass, andwood, and biodiesel production using soybeans andsunflower, will be investigated in this article.

The United States desperately needs a liquid
fuel replacement for oil in the future. The use of oil
is projected to peak about 2007 and the supply isthen projected to be extremely limited in 40–50 years(Duncan and Youngquist, 1999; Youngquist andDuncan, 2003; Pimentel and others, 2004a). Alternative liquid fuels from various sources have beensought for many years. Two panel studies by the
U.S. Department of Energy (USDOE) concernedwith ethanol production using corn and liquid fuelsfrom biomass energy report a negative energy return(ERAB, 1980, 1981). These reports were reviewed by
26 expert U.S. scientists independent of the USDOE;
the findings indicated that the conversion of corn intoethanol energy was negative and these findings were

CORN ETHANOL PRODUCTIONUSING CORN
Shapouri (Shapouri, Duffield, and Wang, 2002;
Shapouri and others, 2004) of the USDA claims thatethanol production provides a net energy return. In
addition, some large corporations, including Archer,
Daniels, Midland (McCain, 2003), support the production of ethanol using corn and are making huge
profits from ethanol production, which is subsidized

1 College of Agriculture and Life Sciences, Cornell University,

Ithaca, New York 14853.
2 Department of Civil and Environmental Engineering, Universityof California, Berkeley California 94720.
whom correspondence should be addressed; e-mail:
dp18@cornell.edu.

3 To

65
C 2005 International Association for Mathematical Geology
1520-7439/05/0300-0065/1 

66
by federal and state governments. Some politiciansalso support the production of corn ethanol basedon their mistaken belief that ethanol production provides large benefits for farmers, whereas in fact farmer
profits are minimal. In contrast to the USDA, numerous scientific studies have concluded that ethanol
production does not provide a net energy balance,that ethanol is not a renewable energy source, is notan economical fuel, and its production and use contribute to air, water, and soil pollution and global
warming (Ho, 1989; Citizens for Tax Justice, 1997;
Giampietro, Ulgiati, and Pimentel, 1997; Youngquist,
1997; Pimentel, 1998, 2001, 2003 NPRA, 2002;
Croysdale, 2001; CalGasoline, 2002; Lieberman, 2002;
Hodge, 2002, 2003; Ferguson, 2003, 2004; Patzek,
2004). Growing large amounts of corn necessaryfor ethanol production occupies cropland suitablefor food production and raises serious ethical issues(Pimentel, 1991, 2003; Pimentel and Pimentel, 1996).
Shapouri (Shapouri, Duffield, and Wang, 2002;
Shapouri and others, 2004) studies concerning thebenefits of ethanol production are incomplete because they omit some of the energy inputs in theethanol production system. The objective of this analysis is to update and assess all the recognized inputs
that operate in the entire ethanol production system.
These inputs include the direct costs in terms of energy
and dollars for producing the corn feedstock as well as
for the fermentation/distillation process. Additionalcosts to the consumer include federal and state subsidies, plus costs associated with environmental pollution and degradation that occur during the entire
production system. Ethanol production in the UnitedStates does not benefit the nation’s energy security, its
agriculture, the economy, or the environment. Also,
ethical questions are raised by diverting land and precious food into fuel and actually adding a net amountof pollution to the environment.
Energy Balance
The conversion of corn and other food/feed crops
into ethanol by fermentation is a well-known and established technology. The ethanol yield from a large
production plant is about 1 l of ethanol from 2.69 kg
of corn grain (Pimentel, 2001).
The production of corn in the United Statesrequires a significant energy and dollar investment(Table 1). For example, to produce average cornyield of 8,655 kg/ha of corn using average production technology requires the expenditure of about
8.1 million kcal for the large number of inputs listed in

Pimentel and Patzek
Table 1 (about 271 gallons of gasoline equivalents/ha).
The production costs are about $917/ha for the
8,655 kg or approximately 11c/ /kg of corn produced.
To produce a liter of ethanol requires 29% more fossil
energy than is produced as ethanol and costs 42c/ per l($1.59 per gallon) (Table 2). The corn feedstock alone
requires nearly 50% of the energy input.
Full irrigation (when there is little or no rainfall)requires about 100 cm of water per growing season.
Only approximately 15% of U.S. corn production currently is irrigated (USDA, 1997a). Of course not allof this requires full irrigation, so a mean value is used.
The mean irrigation for all land growing corn grain is
8.1 cm per ha during the growing season. As a mean

Table 1. Energy Inputs and Costs of Corn Production Per Hectare
in the United States
InputsQuantity

kcal × 1000

Costs $

Labor
Machinery
DieselGasoline
NitrogenPhosphorus
Potassium
Lime
Seeds
Irrigation
Herbicides
Insecticides
Electricity
Transport

11.4 hrsa
55 kgd88 Lg
40 Li
153 kgk
65 kgn
77 kgq1,120 kgt
21 kgv
8.1 cm y
6.2 kgbb
2.8 kgcc
13.2 kWhdd
204 kggg

462b
1,018e1,003h405 j
2,448l
270o
251r
315u
520w
320z
620ee
280ee
34 f f169hh

148.20c103.21 f
34.76
20.80
94.86m40.30 p23.87s
11.00
74.81x123.00aa
124.00
56.00
0.92
61.20

8,115
31,158$916.93kcal input:
output 1:3.84

Total
Corn yield 8,655 kg/haiia NASS, 1999; b It is assumed that a person works 2,000 hr per yr

and utilizes an average of 8,000 l of oil equivalents per yr; c It is
assumed that labor is paid $13 an h; d Pimentel and Pimentel, 1996;
e Prorated per ha and 10 yr life of the machinery. Tractors weighfrom 6 to 7 tons and harvesters 8 to 10 tons, plus plows, sprayers,
and other equipment; f Hoffman, Warnock, and Himman, 1994;
g Wilcke and Chaplin, 2000; h Input 11, 400 kcal per l; i Estimated;
j Input 10,125 kcal per l; k USDA, 2002; l Patzek, 2004; m Cost 62c/
per kg; n USDA, 2002; oInput 4,154 kcal per kg; p Cost $62 perkg; q USDA, 2002; r Input 3,260 kcal per kg; s Cost 31c/ per kg;
t Brees, 2004; u Input 281 kcal per kg; v Pimentel and Pimentel,
1996; w Pimentel, 1980; x USDA, 1997b; y USDA, 1997a; zBatty and
Keller, 1980; aa Irrigation for 100 cm of water per ha costs $1,000(Larsen, Thompson, and Harn, 2002); bb Larson and Cardwell, 1999;
cc USDA, 2002; dd USDA, 1991; ee Input 100,000 kcal per kg of herbicide and insecticide; f f Input 860 kcal per kWh and requires 3 kWhthermal energy to produce 1 kWh electricity; gg Goods transported
include machinery, fuels, and seeds that were shipped an estimated1,000 km; hh Input 0.83 kcal per kg per km transported; ii USDA,
2003a.

Ethanol Production; Biodiesel Production

67

Table 2. Inputs Per 1000 l of 99.5% Ethanol Produced From Corna
InputsCorn grain
Corn transport
Water
Stainless steel
Steel
CementSteamElectricity
95% ethanol
to 99.5%
Sewage effluent
Total

Quantity
2,690 kgb
2,690 kgb
40,000 Le
3 kgi
4 kgi
8 kgi
2,546,000 kcal j
392 kWh j
9 kcal/Lm
20 kg BODn

kcal × 1000 Dollars $2,522b
322c
90 f
12i
12i
8i
2,546 j1,011 j9m

284.25b21.40d
21.16g10.60d10.60d10.60d
21.16k
27.44l
40.00

69h

6.0

6,597

$453.21a Output: 1 l of ethanol = 5,130 kcal; b Data from Table 1; c Calculated

for 144 km roundtrip; d Pimentel, 2003; e 15 l of water mixed witheach kg of grain; f Pimentel and others, 1997; g Pimentel and others,
2004b; h 4 kWh of energy required to process 1 kg of BOD (Blais
and others, 1995); i Slesser and Lewis, 1979; j Illinois Corn, 2004;
k Calculated based on coal fuel; l 7c per kWh; m 95% ethanol con/verted to 99.5% ethanol for addition to gasoline (T. Patzek, pers.
commu., University of California, Berkeley, 2004); n 20 kg of BOD
per 1,000 l of ethanol produced (Kuby, Markoja, and Nackford,
1984).

value, water is pumped from a depth of 100 m (USDA,
1997a). On this basis, the mean energy input associated with irrigation is 320,000 kcal per ha (Table 1).
The average costs in terms of energy and dollars
for a large (245–285 million L/yr), modern ethanol
plant are listed in Table 2. Note the largest energy
inputs are for the corn feedstock, the steam energy,
and electricity used in the fermentation/distillation
process. The total energy input to produce a liter of
ethanol is 6,597 kcal (Table 2). However, a liter of
ethanol has an energy value of only 5,130 kcal. Thus,
there is a net energy loss of 1,467 kcal of ethanol produced. Not included in this analysis was the distribution energy to transport the ethanol. DOE (2002)
estimates this to be 2c//l or approximately more than
331 kcal/l of ethanol.
In the fermentation/distillation process, the corn
is finely ground and approximately 15 l of water are
added per 2.69 kg of ground corn. After fermentation,
to obtain a gallon of 95% pure ethanol from the 8%
ethanol and 92% water mixture, the 1 l of ethanol mustcome from the approximately 13 l of the ethanol/water
mixture. A total of about 13 l of wastewater must be
removed per l of ethanol produced and this sewage
effluent has to be disposed of at both an energy andeconomic cost.
Although ethanol boils at about 78◦ C, whereas
water boils at 100◦ C, the ethanol is not extracted

from the water in just one distillation process. Instead, about 3 distillations are required to obtain the
95% pure ethanol (Maiorella, 1985; Wereko-Brobby
and Hagan, 1996; S. Lamberson, pers. comm. Cornell
Univ. 2000). To be mixed with gasoline, the 95%
ethanol must be processed further and more water
removed requiring additional fossil energy inputs toachieve 99.5% pure ethanol (Table 2). The entire distillation accounts for the large quantities of fossil energy required in the fermentation/distillation process(Table 2). Note, in this analysis all the added energy inputs for fermentation/distillation process total $422.21, including the apportioned energy costs ofthe stainless steel tanks and other industrial materials(Table 2).
About 50% of the cost of producing ethanol(42c/ per l) in a large-production plant is for the corn
feedstock itself (28c//l) (Table 2). The next largest input is for steam (Table 2).
Based on current ethanol production technology
and recent oil prices, ethanol costs substantially more
to produce in dollars than it is worth on the market. Clearly, without the more than $3 billion of federal and state government subsidies each year, U.S.
ethanol production would be reduced or cease, confirming the basic fact that ethanol production is uneconomical (National Center for Policy Analysis, 2002).
Senator McCain reports that including the direct subsidies for ethanol plus the subsidies for corn grain,
a liter costs 79c/ ($3/gallon) (McCain, 2003). If the
production costs of producing a liter of ethanol wereadded to the tax subsidies, then the total cost for aliter of ethanol would be $1.24. Because of the relatively low energy content of ethanol, 1.6 l of ethanol
have the energy equivalent of 1 l of gasoline. Thus, thecost of producing an equivalent amount of ethanol toequal a liter of gasoline is $1.88 ($7.12 per gallon ofgasoline), while the current cost of producing a literof gasoline is 33c/ (USBC, 2003).
Federal and state subsidies for ethanol production that total more than 79c//l are mainly paid tolarge corporations (McCain, 2003). To date, a conservative calculation suggests that corn farmers arereceiving a maximum of only an added 2c/ per bushel
for their corn or less than $2.80 per acre because of
the corn ethanol production system. Some politicians
have the mistaken belief that ethanol production provides large benefits for farmers, but in fact the farmer
profits are minimal. However, several corporations,such as Archer, Daniels, Midland, are making huge
profits from ethanol production (McCain, 2003).
The costs to the consumer are greater than the68$8.4 billion/yr used to subsidize ethanol and corn production because producing the required corn feedstock increases corn prices. One estimate is thatethanol production is adding more than $1 billion to
the cost of beef production (National Center for Policy Analysis, 2002). Because about 70% of the corngrain is fed to U.S. livestock (USDA, 2003a, 2003b),
doubling or tripling ethanol production can be expected to increase corn prices further for beef production and ultimately increase costs to the consumer.
Therefore, in addition to paying the $8.4 billion intaxes for ethanol and corn subsidies, consumers are
expected to pay significantly higher meat, milk, andegg prices in the market place.
Currently, about 2.81 billion gallons of ethanol(10.6 billion l) are being produced in the United Stateseach year (Kansas Ethanol, 2004). The total automotive gasoline delivered in the U.S. was 500 billion l in2003 (USCB, 2004). Therefore, 10.6 billion l of ethanol(equivalent to 6.9 billion l of gasoline) provided only
2% of the gasoline utilized by U.S. automobiles eachyear. To produce the 10.6 billion l of ethanol we use
about 3.3 million ha of land. Moreover significant
quantities of energy are needed to sow, fertilize, andharvest the corn feedstock.
The energy and dollar costs of producing ethanol
can be offset partially by the by-products produced,
similar to the dry distillers grains (DDG) made from
dry-milling. From about 10 kg of corn feedstock,about 3.3 kg of DDG can be harvested that has
27% protein (Stanton, 1999). This DDG has value
for feeding cattle that are ruminants, but has only
limited value for feeding hogs and chickens. The
DDG generally is used as a substitute for soybean
feed that has 49% protein (Stanton, 1999). Soybean
production for livestock production is more energy
efficient than corn production because little or no
nitrogen fertilizer is needed for the production ofthis legume (Pimentel and others, 2002). Only 2.1 kgof 49% soybean protein is required to provide theequivalent of 3.3 kg of DDG. Thus, the credit fossil
energy per liter of ethanol produced is about 445 kcal
(Pimentel and others, 2002). Factoring this credit
in the production of ethanol reduces the negative
energy balance for ethanol production from 29%
to 20% (Table 2). Note that the resulting energy
output/input comparison remains negative even withthe credits for the DDG by-product. Also note thatthese energy credits are contrived because no one
would actually produce livestock feed from ethanol
at great costs in fossil energy and soil depletion(Patzek, 2004).

Pimentel and Patzek
When considering the advisability of producing
ethanol for automobiles, the amount of cropland required to grow sufficient corn to fuel each automobile
should be understood. To make ethanol production
seem positive, we use Shapouri’s (Shapouri, Duffield,
and Wang, 2002; Shapouri and others, 2004) suggestion that all natural gas and electricity inputs beignored and only gasoline and diesel fuel inputs beassessed; then, using Shapouri’s input/output data
results in an output of 775 gallons of ethanol per ha.
Because of its lower energy content, this ethanol has
the same energy as 512 gallons of gasoline. An average U.S. automobile travels about 20,000 miles/yr anduses about 1,000 gallons of gasoline per yr (USBC,
2003). To replace only a third of this gasoline withethanol, 0.6 ha of corn must be grown. Currently, 0.5
ha of cropland is required to feed each American.
Therefore, even using Shapouri’s optimistic data, tofeed one automobile with ethanol, substituting only
one third of the gasoline used per year, Americans
would require more cropland than they need to feedthemselves!
Until recently, Brazil had been the largest producer of ethanol in the world. Brazil used sugarcane to produce ethanol and sugarcane is a more
efficient feedstock for ethanol production than corngrain (Pimentel and Pimentel, 1996). However, theenergy balance was negative and the Brazilian government subsidized the ethanol industry. There thegovernment was selling ethanol to the public for
22c/ per l that was costing them 33c/ per l to produce for sale (Pimentel, 2003). Because of serious
economic problems in Brazil, the government hasabandoned directly subsidizing ethanol (Spirits Low,
1999; Coelho and others, 2002). The ethanol industry is still being subsidized but the consumer ispaying this subsidy directly at the pump (Pimentel,
2003).

Environmental Impacts
Some of the economic and energy contributionsof the by-products mentioned earlier are negatedby the environmental pollution costs associated withethanol production. These are estimated to be morethan 6c/ per l of ethanol produced (Pimentel, 2003).
U.S. corn production causes more total soil erosion that any other U.S. crop (Pimentel and others,
1995; NAS, 2003). In addition, corn production uses
more herbicides and insecticides than any other crop
produced in the U.S. thereby causing more waterEthanol Production; Biodiesel Production
pollution than any other crop (NAS, 2003). Further,corn production uses more nitrogen fertilizer than
any crop produced and therefore is a major contributor to groundwater and river water pollution (NAS,2003). In some Western U.S. irrigated corn acreage,for instance, in some regions of Arizona, groundwater is being pumped 10 times faster than the natural recharge of the aquifers (Pimentel and others,
2004b).
All these factors suggest that the environmental
system in which U.S. corn is being produced is being
rapidly degraded. Further, it substantiates the conclusion that the U.S. corn production system is not environmentally sustainable now or for the future, unlessmajor changes are made in the cultivation of this major food/feed crop. Corn is raw material for ethanol
production, but cannot be considered to provide a renewable energy source.
Major air and water pollution problems also areassociated with the production of ethanol in the chemical plant. The EPA (2002) has issued warnings toethanol plants to reduce their air pollution emissions
or be shut down. Another pollution problem is thelarge amounts of wastewater that each plant produces.
As mentioned, for each liter of ethanol produced using corn, about 13 l of wastewater are produced. This
wastewater has a biological oxygen demand (BOD)of 18,000–37,000 mg/l depending on the type of plant(Kuby, Markoja, and Nackford, 1984). The cost of processing this sewage in terms of energy (4 kcal/kg ofBOD) was included in the cost of producing ethanol(Table 2).
Ethanol contributes to air pollution problems
when burned in automobiles (Youngquist, 1997;
Hodge, 2002, 2003). In addition, the fossil fuels
expended for corn production and later in theethanol plants amount to expenditures of 6,597
kcal of fossil energy per 1,000 l of ethanol produced (Table 2). The consumption of the fossil
fuels release significant quantities of pollutants
to the atmosphere. Furthermore, carbon dioxide
emissions released from burning these fossil fuels
contribute to global warming and are a serious
concern (Schneider, Rosencranz, and Niles, 2002).
When all the air pollutants associated with the entire
ethanol system are measured, ethanol production
contributes to the serious U.S. air pollution problem(Youngquist, 1997; Pimentel, 2003). Overall, if air
pollution problems were controlled and included in
the production costs, then ethanol production costs interms of energy and economics would be significantly
increased.

69
Negative or Positive Energy Return?
Shapouri (Shapouri and others, 2004) of the
USDA now are reporting a net energy positive returnof 67%, whereas in this paper, I report a negative
29% deficit. In their last report, Shapouri, Duffield,
and Wang (2002) reported a net energy positive return of 34%. Why did ethanol production net returnfor the USDA nearly double in 2 yr while corn yields
in the U.S. declined 6% during the past 2 yr (USDA,
2002, 2003a)? Shapouri results need to be examined.
(1) Shapouri (Shapouri and others, 2004) omit
several inputs, for instance, all the energy required to produce and repair farm machinery,
as well as the fermentation-distillation equipment. All the corn production in the U.S. iscarried out with an abundance of farm machinery, including tractors, planters, sprayers,
harvesters, and other equipment. These arelarge energy inputs in corn ethanol production, even when allocated on a life cycle
basis.
(2) Shapouri used corn data from only 9 states,
whereas we use corn data from 50 states.
(3) Shapouri reported a net energy return of 67%
for the co-products, primarily dried-distillers
grain (DDG) used to feed cattle.
(4) Although we did not allocate any energy related to the impacts that the production of
ethanol has on the environment, they are significant in U.S. corn production. (Please see
our previous comments on this subject).
(5) Andrew Ferguson (2004) makes an astuteobservation about the USDA data. The
proportion of sun’s energy that is converted
into useful ethanol, using the USDA’s positive data, only amounts to 5 parts per 10,000.
If the figure of 50 million ha were to be devoted to growing corn for ethanol, then thisacreage would supply only about 11% of U.S.
liquid fuel needs.
(6) Many other investigators support our typeof assessment of ethanol production. (Pleasesee our previous comments on this subject).
Food Versus Fuel Issue
Using corn, a human food resource, for ethanol
production, raises major ethical and moral issues. Today, malnourished (calories, protein, vitamins, iron,and iodine) people in the world number about

70
3.7 billion (WHO, 2000). This is the largest numberof malnourished people and proportion ever reported
in history. The expanding world population that now
number 6.5 billion complicates the food security problem (PRB, 2004). More than a quarter million people
are added each day to the world population, and eachof these human beings requires adequate food.
Malnourished people are highly susceptible tovarious serious diseases; this is reflected in the rapid
rise in number of seriously infected people in theworld as reported by the World Health Organization(Kim, 2002).
The current food shortages throughout the world
call attention to the importance of continuing U.S. exports of corn and other grains for human food. Cereal
grains make up 80% of the food of the people worldwide. During the past 10 years, U.S. corn and othergrain exports have nearly tripled, increasing U.S. export trade by about $3 billion per yr (USBC, 2003).
Concerning the U.S. balance of payments, theU.S. is importing more than 61% of its oil at a costof more than $75 billion per yr (USBC, 2003). Oil
imports are the largest deficit payments incurred by
the United States (USBC, 2003). Ethanol production requires large fossil energy input, therefore, it
is contributing to oil and natural gas imports and U.S.
deficits (USBC, 2003).
At present, world agricultural land based on
calories supplies more than 99.7% of all world food(calories), while aquatic ecosystems supply less than
0.3% (FAO, 2001). Already worldwide, during the last
decade per capita available cropland decreased 20%,
irrigation 12%, and fertilizers 17% (Brown, 1997).
Expanding ethanol production could entail diverting valuable cropland from producing corn needed
to feed people to producing corn for ethanol factories. The practical aspects, as well as the moral andethical issues, should be seriously considered before
steps are taken to convert more corn into ethanol for
automobiles.

SWITCHGRASS PRODUCTION
OF ETHANOL
The average energy input per hectare for switchgrass production is only about 3.8 million kcal per yr(Table 3). With an excellent yield of 10 t/ha/yr, thissuggests for each kcal invested as fossil energy the
return is 11 kcal—an excellent return. If pelletized
for use as a fuel in stoves, the return is reported to
be about 1:14.6 kcal (Samson, Duxbury, and Mulkins,

Pimentel and Patzek
Table 3. Average Inputs and Energy Inputs Per Hectare Per Yearfor Switchgrass Production
Input

Quantity

103 kcal

Dollars

Labor
Machinery
DieselNitrogen
Seeds
Herbicides

5 hra
30 kgd100 Le50 kge1.6 kg f
3 kgg

20b
555
1,000
800
100a
300h

$65c
50a
50
28e
3f
30a

10,000 kg yieldi
40 million
kcal yield

2,755
input/
output ratio$230 j
1:14.4k

Total

a Estimated; b Average person works 2,000 h per yr and uses about

8,000 l of oil equivalents. Prorated this works out to be 20,000kcal; c The agricultural labor is paid $13 per h; d The machinery
estimate also includes 25% more for repairs; e Calculated basedon data from David Parrish (pers. comm., Virginia Technology
University, 2005); f Data from Samson, 1991; g Calculated basedon data from Henning, 1993; h 100,000 kcal per kg of herbicide;i Samson and others, 2000; j Brummer and others, 2000 estimateda cost of about $400/ha for switchgrass production. Thus, the $268
total cost is about 49% lower that what Brummer and others (2000)
estimates and this includes several inputs not included in Brummer
and others (2000); kSamson and others (2000) estimated an input
per output return of 1:14.9, but I have added several inputs notincluded in Samson and others (2000). The input/output returns,
however, are similar.

2004). The 14.6 is higher than the 11 kcal in Table 3,
because here a few more inputs were included thanin Samson, Duxbury, and Mulkins, (2004) report. The
cost per ton of switchgrass pellets ranges from $94
to $130 (Samson, Duxbury, and Mulkins, 2004). This
seems to be an excellent price per ton.
However, converting switchgrass into ethanol results in a negative energy return (Table 4). The negative energy return is 50% or slightly higher than thenegative energy return for corn ethanol production(Tables 2 and 4). The cost of producing a liter of
ethanol using switchgrass was 54c/ or 9c/ higher than
the 45c/ per l for corn ethanol production (Tables 2 and
4). The two major energy inputs for switchgrass conversion into ethanol were steam and electricity production (Table 4).

WOOD CELLULOSE CONVERSION
INTO ETHANOL
The conversion of 2,500 kg of wood harvested
from a sustainable forest into 1,000 l of ethanol require an input of about 9.0 million kcal (Table 5).
Therefore, the wood cellulose system requires slightly

Ethanol Production; Biodiesel Production

71

Table 4. Inputs Per 1000 l of 99.5% Ethanol Produced From
U.S. Switchgrass
InputsSwitchgrass
Transport,
switchgrass
Water
Stainless steel
Steel
CementGrind switchgrass
Sulfuric acid
Steam production
Electricity
Ethanol conversion
to 99.5%
Sewage effluent
Total

Quantities

kcal × 1000a

Costs

2,500 kgb
2,500 kgd

694c
300

$250o
15

125,000 kge
3 kgg
4 kgg
8 kgg
2,500 kg
118 kgi
8.1 tonsi
660 kWhi
9 kcal/L j

70 f
45g
46g
15g
100h
0
4,404
1,703
9

20m
11g
11g
11g
8h
83n
36
46
40

20 kg (BOD)k

69l

6

7,455

$537

Table 5. Inputs Per 1000 l of 99.5% Ethanol Produced From U.S.
wood cellulose
InputsQuantities kcal × 1000a

Costs

Wood, harvest (fuel)Machinery
Replace nitrogen
Transport, wood
Water
Stainless steel
Steel
CementGrind wood
Sulfuric acid
Steam production
Electricity
Ethanol conversion
to 99.5%
Sewage effluent

2,500 kgb

400c

5 kgm
50 kgc2,500 kgd
125,000 kge
3 kgg
4 kgg
8 kgg
2,500 kg
118 kgb
8.1 tonsb
666 kWhbl
9 kcal/Li

100m
800
300
70 f
45g
46g
15g
100h
0
4,404
1,703
9

$ 250n
10o
28o
15
20o
11g
11g
11g
8h
83 p
36
46
40

20 kg (BOD) j

69k

6

8,061

$575

Total
Note. Requires 45% more fossil energy to produce 1 l of ethanolusing 2.5 kg switchgrass than the energy in a liter of ethanol. Total
cost per liter of ethanol is 54c/. A total of 0.25 kg of brewers yeast(80% water) was produced per 1,000 l of ethanol produced. This
brewers yeast has a feed value equivalent in soybean meal of about
480 kcal.
a Outputs: 1000 l of ethanol = 5.13 million kcal; b Samson (1991)
reports that 2.5 kg of switchgrass is required to produce 1 l ofethanol; c Data from Table 1 on switchgrass production; d Estimated144 km roundtrip; e Pimentel and others, 1988; f Estimated waterneeds for the fermentation program; g Slesser and Lewis, 1979;h Calculated based on grinder information (Wood Tub Grinders,
2004); i Estimated based on cellulose conversion (Arkenol, 2004);
j 95% ethanol converted to 99.5% ethanol for addition to gasoline(T. Patzek, pers. comm., University of California, Berkeley, 2004);
k 20 kg of BOD per 1,000 l of ethanol produced (Kuby, Markoja,
and Nactford, 1984); l 4 kWh of energy required to process 1 kg
(Blais and others, 1995); mPimentel, 2003; n Sulfuric acid sells for$7 per kg. It is estimated that the dilute acid is recycled 10 times;
o Samson, Duxbury, and Mulkins, 2004.

more energy to produce the 1,000 l of ethanol thanusing switchgrass (Tables 4 and 5). About 57% moreenergy is required to produce a liter of ethanol usingwood than the energy harvested as ethanol.
The ethnaol cost per liter for wood-produced
ethanol is slightly higher than the ethanol produced
using switchgrass, 58c/ versus 54c/, respectively (Tables
4 and 5). The two largest fossil energy inputs in thewood cellulose production system were steam andelectricity (Table 5).
SOYBEAN CONVERSION INTO BIODIESEL
Various vegetable oils have been converted into
biodiesel and they work well in diesel engines. An
assessment of producing sunflower oil proved toNote. Requires 57% more fossil energy to produce 1 l of ethanolusing 2 kg wood than the energy in a liter of ethanol. Total cost
per liter of ethanol is 58c/. A total of 0.2 kg of brewers yeast (80%water) was produced per 1,000 l of ethanol produced. This brewers
yeast has a feed value equivalent in soybean meal of 467 kcal.
a Outputs: 1000 l of ethanol = 5.13 million kcal; b Arkenol (2004)
reported that 2 kg of wood produced 1 l of ethanol. We question this 2 kg to produce 1 l of ethanol when it takes 2.69 kg ofcorn grain to produce 1 l of ethanol. Others are reporting 13.2 kgof wood per kg per l of ethanol (DOE, 2004). We used the optimistic figure of 2.5 kg of wood per l of ethanol produced; c 50 kg ofnitrogen removed with the 2,500 kg of wood (Kidd and Pimentel,
1992); d Estimated 144 km roundtrip; e Pimentel and others, 1988;
f Estimated water needs for the fermentation program; g Slesser
and Lewis, 1979; h Calculated based on grinder information (Wood
Tub Grinders, 2004); i 95% ethanol converted to 99.5% ethanol
for addition to gasoline (T. Patzek, pers. comm., University ofCalifornia, Berkeley, 2004); j 20 kg of BOD per 1,000 l of ethanol
produced (Kuby, Markoja, and Nackford, 1984); k4 kWh of energy required to process 1 kg (Blais and others, 1995); l Illinois
Corn, 2004; mMead and Pimentel, 2004; n Samson, Duxbury, andMulkins, 2004; oPimentel, 2003; p Sulfuric acid sells for $7 per kg.
It is estimated that the dilute acid is recycled 10 times.

be energy negative and costly in terms of dollars(Pimentel, 2001). Although soybeans contain less oil
than sunflower, about 18% soy oil compared with
26% oil for sunflower, soybeans can be produced
without or nearly zero nitrogen (Table 6). This
makes soybeans advantageous for the productionof biodiesel. Nitrogen fertilizer is one of the mostenergy costly inputs in crop production (Pimentel
and others, 2002).
The yield of sunflower also is lower thansoybeans, 1,500 kg/ha for sunflower compared with
2,668 kg/ha for soybeans (USDA, 2003a). The production of 2,668 kg/ha of soy requires an input of72

Pimentel and Patzek

Table 6. Energy Inputs and Costs in Soybean Production Per
Hectare in the U.S.

Inputs

InputsQuantity

kcal × 1000

Costs $

Labor
Machinery
DieselGasoline
LP gasNitrogenPhosphorus
Potassium
Lime
Seeds
Herbicides
Electricity
Transport

7.1 ha20 kgd38.8 La
35.7 La
3.3 La3.7 kg j
37.8 kg j
14.8 kg j
4800 kgv
69.3 kga
1.3 kg j
10 kWhd
154 kgt

284b
360e
442g
270h
25i
59k
156m
48o
1,349d
554q
130e
29s
40u

92.30c148.00 f
20.18
13.36
1.20
2.29l
23.44n4.59 p110.38v
48.58r
26.00
0.70
46.20

3,746
9,605

$537.22kcal input:
output 1:2.56

Total
Soybean yield 2,668 kg/haw

Table 7. Inputs Per 1,000 kg of Biodiesel Oil From Soybeansa Ali and McBride, 1990; b It is assumed that a person works 2,000 h

per yr and utilizes an average of 8,000 l of oil equivalents per yr;
c It is assumed that labor is paid $13 an h; d Pimentel and Pimentel,

1996; e Machinery is prorated per hectare and a 10 yr life of themachinery. Tractors weigh from 6 to 7 tons and harvestors from 8
to 10 tons, plus plows, sprayers, and other equipment; f College ofAgri., Consumer and Environ. Sciences, 1997. g Input 11,400 kcal
per l; h Input 10,125 kcal per l; i Input 7,575 kcal per l; j Economic
Research Statistics, 1997; kPatzek, 2004; l Hinman and others, 1992;
m Input 4,154 kcal per kg; n Cost 62c per kg; o Input 3,260 kcal per kg;/
p Costs 31c per kg; q Pimentel and others, 2002; r Costs about 70c per//kg; s Input 860 kcal per kWh and requires 3 kWh thermal energy to
produce 1 kWh electricity; t Goods transported include machinery,fuels, and seeds that were shipped an estimated 1,000 km; u Input
0.83 kcal per kg per km transported; v Kassel and Tidman, 1999;
Mansfield, 2004; Randall and Vetsch, 2004; w USDA, 2003a, 2003b.

about 3.7 million kcal per ha and costs about $537/ha(Table 6).
With a yield of oil of 18% then 5,556 kg ofsoybeans are required to produce 1,000 kg of oil(Table 7). The production of the soy feedstock requires an input of 7.8 million kcal. The second largest
input is steam that requires an input of 1.4 million
kcal (Table 7). The total input for the 1,000 kg of soy
oil is 11.4 million kcal. With soy oil having an energy
value of 9 million kcal, then there is a net loss of
32% in energy. However, a credit should be taken forthe soy meal that is produced and this has an energy
value of 2.2 million kcal. Adding this credit to soybean oil credit, then the net loss in terms of energy
is 8% (Table 7). The price per kg of soy biodiesel is$1.21, however, taking credit for the soy meal would
reduce this price to 92c/ per kg of soy oil (Note, soy
oil has a specific gravity of about 0.92, thus soy oilvalue per liter is 84c/ per l. This makes soy oil about

Soybeans
Electricity
Steam
Cleanup waterSpace heat
Direct heat
LossesStainless steel
Steel
Cement
Total

Quantity

kcal × 1000

5,556 kga
270 kWhb
1,350,000 kcalb
160,000 kcalb
152,000 kcalb
440,000 kcalb
300,000 kcalb
11 kg f
21 kg f
56 kg f

7,800a697c
1,350b
160b
152b
440b
300b
158 f
246 f
106 f
11,878

Costs $
$1,117.42a
18.90d
11.06e
1.31e
1.24e
3.61e
2.46e
18.72g18.72g18.72g$1,212.16

Note. The 1,000 kg of biodiesel produced has an energy value of
9 million kcal. With an energy input requirement of 11.9 million
kcal, there is a net loss of energy of 32%. If a credit of 2.2 million
kcal is given for the soy meal produced, then the net loss is 8%.
The cost per kg of biodiesel is $1.21.
a Data from Table 6; b Data from Singh, 1986; c An estimated
3 kWh thermal is needed to produce a kWh of electricity; d Cost
per kWh is 7c/; e Calculated cost of producing heat energy using
coal; f Calculated inputs using data from Slesser and Lewis, 1979;g Calculated costs from Pimentel, 2003.

2.8 times as expensive as diesel fuel). This makes soy
oil expensive compared with the price of diesel thatcosts about 30c/ per l to produce (USBC, 2003).
Sheehan and others (1998, p. 13) of the Department of Energy also report a negative energy returnin the conversion of soybeans into biodiesel. They report “1 MJ of biodiesel requires an input of 1.24 MJ
of primary energy.”
Soybeans are a valuable crop in the UnitedStates. The target price reported by the USDA
(2003a) is 21.2c//kg while the price calculated inTable 6 for average inputs per hectare is 20.1c//kg.
These values are close.
SUNFLOWER CONVERSION
INTO BIODIESELIn a preliminary study of converting sunflower
into biodiesel fuel, as mentioned, the result in termsof energy output was negative (Pimentel, 2001). In
the current assessment, producing sunflower seeds
for biodiesel yields 1,500 kg/ha (USDA, 2003a) orslightly higher than the 2001 yield. The 1,500 kg/ha
yield is still significantly lower than soybean and corn
production per ha.
The production of 1,500 kg/ha of sunflower seeds
requires a fossil energy input of 6.1 million kcal
(Table 8). Thus, the kcal input per kcal output is negative with a ratio of 1:0.76 (Table 8). Sunflower seeds

Ethanol Production; Biodiesel Production

73

Table 8. Energy Inputs and Costs in Sunflower Production Per Ha
in the U.S.

Inputs

InputsQuantity

kcal × 1000

Costs $

Labor
Machinery
DieselNitrogenPhosphorus
Potassium
Lime
Seeds
Herbicides
Electricity
Transport

8.6 ha20 kgd180 La110 kg j
71 kg j
100 kg j1000 kg j
70 kga3 kg j
10 kWhd
270 kgt344b
360e
1,800g
1,760k
293m
324o
281d
560q
300v
29s
68u

111.80c
148.00 f
93.62h68.08l44.03n34.11 p23.00v
49.07r
60.00i
0.70
81.00

6,119
4,650

$601.61
kcal input:
output 1:0.76

Total
Sunflower yield 1,500 kg/haw

Table 9. Inputs Per 1,000 kg of Biodiesel Oil From Sunflower

a Knowles and Bukantis, 1980; b It is assumed that a person works

2,000 h per year and utilizes an average of 8,000 l of oil equivalents
per yr; c It is assumed that labor is paid $13 an h; d Pimentel andPimentel, 1996; e Machinery is prorated per ha and a 10 yr life of
the machinery. Tractors weigh from 6 to 7 tons and harvestors from
8 to 10 tons, plus plows, sprayers, and other equipment; f College ofAgriculture, Consumer and Environ. Sciences, 1997; g Input 10,000
kcal per l; h 52c/ per l; i $20 per kg; j Blamey, Zollinger, and Schneiter,
1997; kPatzek, 2004; l Hinman and others, 1992; mInput 4,154 kcal
per kg; n Cost 62c/ per kg; oInput 3,260 kcal per kg; p Costs 31c/ per kg;
q Based on 7,900 kcal per kg of sunflower seed production; r Costs
about 70c/ per kg; s Input 860 kcal per kWh and requires 3 kWhthermal energy to produce 1 kWh electricity; t Goods transported
include machinery, fuels, and seeds that were shipped an estimated1,000 km; u Input 0.83 kcal per kg per km transported; v 100,000 kcalof energy required per kg of herbicide; w USDA, 2003a, 2003b.

have higher oil content than soybeans, 26% versus
18%. However, the yield of sunflower is nearly one
half that of soybean.
Thus, to produce 1,000 kg of sunflower oil
requires 3,920 kg of sunflower seeds with an energy
input of 156.0 million kcal (Table 9). This is the largest
energy input listed in Table 9. Therefore, to produce
1,000 kg of sunflower oil with an energy content of
9 million kcal, the fossil energy input is 118% higher
than the energy content of the sunflower biodiesel
and the calculated cost is $1.66 per kg of sunflower
oil (Table 9) (Note, the specific gravity of sunflower
oil is 0.92, thus the cost of a liter of sunflower oil is$1.53 per l).

CONCLUSION
Several physical and chemical factors limit the
production of liquid fuels such as ethanol andSunflower
Electricity
Steam
Cleanup waterSpace heat
Direct heat
LossesStainless steel
Steel
Cement
Total

Quantity

kcal × 1000

Costs $

3,920 kga
270 kWhb
1,350,000 kcalb
160,000 kcalb
152,000 kcalb
440,000 kcalb
300,000 kcalb
11 kg f
21 kg f
56 kg f15,990a697c
1,350b
160b
152b
440b
300b
158 f
246 f
106 f

$1.570.20a
18.90d
11.06e
1.31e
1.24e
3.61e
2.46e
18.72g18.72g18.72g

19,599$1,662.48

Note. The 1,000 kg of biodiesel produced has an energy value of
9 million kcal. With an energy input requirement of 19.6 million
kcal, there is a net loss of energy of 118%. If a credit of 2.2 million
kcal is given for the soy meal produced, then the net loss is 96%.
The cost per kg of biodiesel is $1.66.
a Data from Table 8; b Data from Singh, 1986; c An estimated
3 kWh thermal is needed to produce a kWh of electricity; d Cost
per kWh is 7c/; e Calculated cost of producing heat energy using
coal; f Calculated inputs using data from Slesser and Lewis, 1979;g Calculated costs from Pimentel, 2003.

biodiesel using plant biomass materials. These include
the following:(1) An extremely low fraction of the sunlightreaching America is captured by plants. On
average the sunlight captured by plants isonly about 01.%, with corn providing 0.25%.
These low values are in contrast to photovoltaics that capture from 10% or more sunlight, or approximately 100-fold more sunlight than plant biomass.
(2) In ethanol production the carbohydrates
are converted into ethanol by microbes,
that on average bring the concentration of
ethanol to 8% in the broth with 92% water.
Large amounts of fossil energy are required
to remove the 8% ethanol from the 92%
water.
(3) For biodiesel production, there are two problems: the relatively low yields of oil crops
ranging from 1,500 kg/ha for sunflower toabout 2,700 kg/ha for soybeans; sunflower
averages 25.5% oil, whereas soybeans average 18% oil. In addition, the oil extraction processes for all oil crops is highly energy intensive as reported in this manuscript.
Therefore, these crops are poor producers ofbiomass energy.

74
ACKNOWLEDGMENTS
We wish to thank the following people for theirhelpful comments and suggestions on earlier draftsof the manuscript: A. Ferguson, Senior Researcher,
Optimum Population Trust, Manchester, UK; P.
Harriot, Chemical Engineering, Cornell University,
Ithaca, NY; M. Mrini, Centre Technique des Cultures Sucrieres, Kenitra, Morocco; D. Parrish, Cropand Soil Environmental Science, Virginia Technology University, Blacksburg, VA; W. Youngquist,
Consulting Geologist, Eugene, OR; M. Pimentel,
Division of Nutritional Sciences, Cornell University,
Ithaca, NY; A. Wilson, Research Assistant, Cornell
University, Ithaca, NY.
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