[Editors] MIT ethanol analysis confirms benefits of biofuels

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT ethanol analysis confirms benefits of biofuels
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For Immediate Release
MONDAY, JAN. 8, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

CAMBRIDGE, Mass.--Controversy over the benefits of using corn-based 
ethanol in vehicles has been fueled by studies showing that 
converting corn into ethanol may use more fossil energy than the 
energy contained in the ethanol produced. Now a new MIT analysis 
shows that the energy balance is actually so close that several 
factors can easily change whether ethanol ends up a net energy winner 
or loser.

Regardless of the energy balance, replacing gasoline with corn-based 
ethanol does significantly reduce oil consumption because the biomass 
production and conversion process requires little petroleum. And 
further MIT analyses show that making ethanol from cellulosic sources 
such as switchgrass has far greater potential to reduce fossil energy 
use and greenhouse gas emissions.

The Bush administration is pushing the use of ethanol as a 
domestically available, non-petroleum alternative to gasoline. But 
most U.S. ethanol is now made from corn, and growing corn and 
converting the kernels into ethanol consume a lot of 
energy-comparable to what is contained in the ethanol produced. 
Making ethanol from corn stalks, other agricultural wastes and wild 
grasses would consume less energy, but the technology for converting 
them to ethanol may not be economically viable for another five or so 
years.

Does using corn-based ethanol in place of gasoline actually make 
energy consumption and emissions go up, as some researchers claim? 
Why do others reach the opposite conclusion? And how much better 
would ethanol from "cellulosic" feedstocks such as switchgrass be?

To answer those questions, Tiffany A. Groode, a graduate student in 
MIT's Department of Engineering, performed her own study, supervised 
by John B. Heywood, Sun Jae Professor of Mechanical  Engineering.

Using a technique called life cycle analysis, she looked at energy 
consumption and greenhouse gas emissions associated with all the 
steps in making and using ethanol, from growing the crop to 
converting it into ethanol. She limited energy sources to fossil 
fuels. Finally, she accounted for the different energy contents of 
gasoline and ethanol. Pure ethanol carries 30 percent less energy per 
gallon, so more is needed to travel a given distance.

While most studies follow those guidelines, Groode added one more 
feature: She incorporated the uncertainty associated with the values 
of many of the inputs. Following a methodology developed by recent 
MIT graduate Jeremy Johnson (Ph.D. 2006), she used not just one value 
for each key variable (such as the amount of fertilizer required), 
but rather a range of values along with the probability that each of 
those values would occur. In a single analysis, her model runs 
thousands of times with varying input values, generating a range of 
results, some more probable than others.

Based on her "most likely" outcomes, she concluded that traveling a 
kilometer using ethanol does indeed consume more energy than 
traveling the same distance using gasoline. However, further analyses 
showed that several factors can easily change the outcome, rendering 
corn-based ethanol a "greener" fuel.

One such factor is the much-debated co-product credit. When corn is 
converted into ethanol, the material that remains is a high-protein 
animal feed. One assumption is that the availability of that feed 
will enable traditional feed manufacturers to produce less, saving 
energy; ethanol producers should therefore get to subtract those 
energy savings from their energy consumption. When Groode put 
co-product credits into her calculations, ethanol's life-cycle energy 
use became lower than gasoline's.

Another factor that influences the outcome is which energy-using 
factors of production are included and excluded-the so-called system 
boundary. A study performed by Professor David Pimentel of Cornell 
University in 2003 includes energy-consuming inputs that other 
studies do not, one example being the manufacture of farm machinery. 
His analysis concludes that using corn-based ethanol yields a 
significant net energy loss. Other studies conclude the opposite.

To determine the importance of the system boundary, Groode compared 
her own analysis, the study by Pimentel and three other reputable 
studies, considering the same energy-consuming inputs and no 
co-product credits in each case.

"The results show that everybody is basically correct," she said. 
"The energy balance is so close that the outcome depends on exactly 
how you define the problem." The results also serve to validate her 
methodology: Results from the other studies fall within the range of 
her more probable results.

Growing more corn may not be the best route to expanding ethanol 
production. Other options include using corn stover (the plants and 
husks that are left on the field), or growing an "energy crop" such 
as switchgrass. While corn kernels are mostly starch, corn stover and 
switchgrass are primarily cellulose. Commercial technologies to make 
ethanol from cellulose are not yet available, but laboratory and 
pilot-scale tests are generating useful data on processing 
techniques. So how do cellulosic sources measure up in terms of 
saving energy and reducing greenhouse gas emissions?

Using her methodology, Groode performed an initial analysis of 
switchgrass and, drawing again on Johnson's work, corn stover. She 
found that fossil energy consumption is far lower with these two 
cellulosic sources than for the corn kernels.

Farming corn stover requires energy only for harvesting and 
transporting the material. (Fertilizer and other inputs are assumed 
to be associated with growing the kernels.) Growing switchgrass is 
even less energy intensive. It requires minimal fertilizer, its life 
cycle is about 10 years, so it need not be replanted each year, and 
it can be grown almost anywhere, so transport costs can be minimized.

Groode and Heywood now view the three ethanol sources as a continuum. 
In the future, cellulosic sources such as corn stover and ultimately 
switchgrass can provide large quantities of ethanol for widespread 
use as a transportation fuel. In the meantime, ethanol made from corn 
can provide some immediate benefits.

"I view corn-based ethanol as a stepping-stone," said Groode. "People 
can buy flexible-fuel vehicles right now and get used to the idea 
that ethanol or E85 works in their car. If ethanol is produced from a 
more environmentally friendly source in the future, we'll be ready 
for it."

This research was supported by BP America.

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Written by Nancy Stauffer, MIT Laboratory for Energy and the Environment