Key Differences between Pimentel/Patzek Study and Other Studies

Key Differences between Pimentel/Patzek Study and Other Studies

By Michael Wang
Center for Transportation Research
Argonne National Laboratory

July 19, 2005

The recent article by Pimentel/Patzek concludes that:

1.      Corn ethanol requires 29% more fossil energy than ethanol contains
2.      Herbaceous cellulosic ethanol requires 50% more fossil energy
3.      Woody cellulosic ethanol requires 57% more fossil energy
4.      Soybean-based biodiesel requires 27% more fossil energy than biodiesel 
contains
5.      and sunflower-based biodiesel requires 118% more fossil energy

In contrast, many other studies, including Argonneâ??s study, conclude that 
corn ethanol, cellulosic ethanol, and biodiesel require less fossil energy than 
each of the fuel contains. In particular, Argonneâ??s study concludes:

1.      Corn ethanol requires 26% less fossil energy
2.      Cellulosic ethanol requires 90% less fossil energy

In addition, NREL study sponsored by DOE and USDA in 1998 concludes that 
soybean-based biodiesel requires 69% less fossil energy than biodiesel contains.

A review of Pimentel/Patzek reveals that they made pessimistic assumptions, had 
double-counted certain energy costs without detailed elaboration. Below is a 
quick summary of the key differences between Pimentel/Patzek and others.

A.  Corn Ethanol:

1.      Corn farming energy use:

a)      Pimentel/Patzek conclude that corn farming requires 94,504 Btu/bushel, 
with 18.2% from farmer labor and farming machinery (77,304 Btu/bushel excluding 
farmer labor and farming machinery)
b)      A 2002 detailed USDA analysis showed that corn farming requires 57,480 
Btu/bushel (excluding farmer labor and farming machinery)
c)      Pimentel/Patzek overestimate corn farming energy use (excluding farmer 
labor and farming machinery) by 34%
d)      It also appears that Pimentel and Patzek overestimate energy use 
related to farmer labor and farming machinery

2.      Ethanol production energy use:

a)      Pimentel/Patzek conclude that ethanol production at ethanol plants 
consumes 56,440 Btu/gal. (56,000 Btu/gal, excluding energy embedded in ethanol 
plant construction materials)
b)      A detailed survey of ethanol plant energy use in 2001 showed an energy 
use of 48,770 Btu/gal. for dry mill ethanol plants and 54,240 Btu/gal., with an 
average of 53,010 Btu/gal in 2001.
c)      Recent dry mill plants (all new ethanol plants coming online in recent 
years have been dry mill plants) may have energy use of 42,530 Btu/gal.
d)      Pimentel/Patzek overestimate ethanol plant energy use by up to 30%
e)      Pimentel/Patzek assume an ethanol yield of 2.5 gallons per bushel of 
corn. Ethanol plants now produce ethanol at 2.7 gallons/bushel and they are 
approaching the yield of 2.8 gallons/bushel.

3.      Animal feed co-products from corn ethanol plants:

a)      Pimentel/Patzekâ??s 29% increase in fossil energy by corn ethanol gives 
not credit to animal feeds
b)      Pimentel/Patzek acknowledge that animal feeds could have an energy 
credit of 6,680 Btu per gallon of ethanol produced
c)      Argonneâ??s conservative estimation shows that animal feeds and other 
coproducts from ethanol plants have an energy credit of 12,030 Btu per gallon 
of ethanol produced

B.  Cellulosic Ethanol:

The key difference between Pimentel/Patzek and other studies is how steam and 
electricity needed for cellulosic ethanol plant operations is generated. 

Cellulosic biomass contains more than 25% of lignin, which may not be fermented 
into ethanol. For cellulosic ethanol designs supported by DOE and others, the 
lignin portion of biomass feedstocks is to be burned to provide steam and 
electricity for cellulosic ethanol plant operations. In fact, cellulosic 
ethanol plants will generate an excess amount of electricity for exporting to 
the electric grid.

To the contrary of the commonly accepted cellulosic ethanol plant designs, 
Pimentel/Patzek assume that fossil fuels are to be burned in cellulosic ethanol 
plants to generate needed steam and electricity. 

If Pimentel/Patzek assumed use of lignin to produce steam and electricity in 
cellulosic ethanol plants, they would have had positive energy balance values 
for cellulosic ethanol similar to those from Argonne and others.

C.  Biodiesel:

DOE and USDA in 1998 funded a study evaluating soybean-based biodiesel. That 
study concluded biodiesel consumes 69% less fossil energy. Argonne has not 
evaluated biodiesel.

D. Costs Results by Pimentel/Patzek

Pimentel/Patzek present cost estimates for corn, soybeans, switchgrass, woody 
biomass, soybeans, sunflowers, ethanol, and biodiesel. Argonne has not 
conducted cost estimates. Argonneâ??s review of Pimentel/Patzek shows that 
their production cost estimates are higher than market prices, implying that 
farmers, ethanol producers, biodiesel producers are in money-losing business, 
even taking into account subsidies they receive. 

Argonne also found that Pimentel/Patzek cost estimates for cellulosic ethanol 
contain calculation errors by using a cost of $100 per tonne for cellulosic 
biomass feedstock, instead of their own estimate of $23 per tonne.

E.  General Issues:

1.      Though self evaluation of ethanolâ??s energy balance is easy to 
understand, it does not reveal the true energy benefit of ethanol in replacing 
gasoline; a meaningful way for energy policy debates is to compare ethanol and 
gasoline to assess the relative merit of ethanol. It is important to put a 
given energy product into a broad perspective with other energy products for 
serving same functions in society.
2.      Decisions on pursuing certain energy products by society have not been 
based on their energy balance values. For example, even though electricity 
generation has a huge negative energy balance value (2.3 unit of fossil energy 
input for a unit of electric energy output in the US), we do not question the 
practice of electricity generation. The quality of energy products should be 
taken into account in making energy choices. 
3.      In conclusion, energy balance calculations for individual energy 
productions in their isolations could be arbitrary; results are less meaningful 
or could be misleading.


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