Mazda to Put Tribute Hybrid on Market in 2Q
BNSF Railway Considering Coal-to-Liquids Plant in Montana

MIT Analysis Describes Energy Benefits of Ethanol

Click to enlarge.

A recent MIT analysis shows that the energy balance of corn ethanol is actually so close that several factors can easily change whether ethanol derived from that process ends up a net energy winner or loser. Further analysis shows that making ethanol from cellulosic sources such as switchgrass has far greater potential to reduce fossil energy use and greenhouse gas emissions.

A graduate student in MIT’s Department of Engineering, Tiffany A. Groode, performed a life cycle analysis on the production of corn ethanol, as others have done. Groode, however, 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 corn 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. The energy balance is so close that the outcome depends on exactly how you define the problem.

—Tiffany Groode

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, or growing an energy crop such as switchgrass. 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 supervisor supervised by John Heywood, Sun Jae Professor of Mechanical Engineering, 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. 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.

—Tiffany Groode

This research was supported by BP America.




Love the history! So, maybe, just maybe a plan to wean the big ADM subsidies for corn and make them available to other alt fuel producers, i.e. smaller cellulosic farmers, biodiesel farmers AND begin removing the confiscatory ban on Brazilian sugar/ethanol - we might just speed our transition to flex fueled vehicles.

The Whiskey Rebellion came about when federal government needed to pay their debts for the revolution. So they taxed the cash crops of Pennsylvania farmers.

"...these westerners, mostly farmers, were considered backward and a little slow-witted, so it was assumed that one could tax them with impunity."

Unfortunately a sentiment that continues to this day at the depths of fed thinking.


re: gr - Actually, the US was founded on credit and paid for with excise taxes until 1817 when it switched to import taxes. The economy then boomed right up until the Civil War and the 1861 emergency income tax.

I suspect the real issue in the Whiskey Rebellion was not the issue of "a" tax but the question of fairness. Small farmers had to pay 50% more in coin than the large rum producers had to pay on credit. And this was after the British had pulled so many similar stunts. For example the legal notary tax was 2 pounds in the UK but 10 pounds in the colonies.

But to return to the orginal topic here, is ethanol economically viable? The answer is yes, if the government would stop interfering. Also, even a moderate ammount of ethanol helps the remaining gas burn much cleaner and it supports a higher compression ratio allowing more power out of a smaller, lighter engine.

An Engineer

You are exaggerating, I'm affraid. In stating that ethanol costs $0.08/liter ($0.30/gal), I presume you are referring to Chart #4, titled "Gross Feedstock Costs per Litre (sic) of Ethanol". So it does not include production costs. According to USDA, production costs adds on average ~$0.37/gal (2002), to get us to $0.67/gal. Admittedly, production costs may be cheaper in Brazil, so $0.45/gal may be possible.

But of course, that's only O&M, to pay for your ethanol plant (unless Santa Claus is moving into construction) you need to add between $1.05 and $3.00 per USDA. So, you're up to $1.50/gal, best case.


I really don't think that the energy efficiency of EtOH as a fuel is the main point.

I am concerned about the deleterious health effects on society from remaining on a benzene based fuel source.

EtOH is clearly a more logical choice from a health standpoint. And ultimately, this point should trump all others.


re: Engineer

I clearly state "The production price of the sugar used in Brazil" not 'the total cost of ethanol' as a response to your unsubstantiated (and wrong, anyone can google it) claim about the ammount of ethanol yielded from corn.

I invite everyone to read the links. Ethanol is cheaper outside the US than gasoline is. It's a fact. Stop making convoluted arguments about why it's not possible. I invite everyone to go check the prices in Brazil or India compared to the US.

Only government interference keeps the price so high here.

An Engineer

I invite everyone to read the links. Excellent idea. From your link:
In the mid-1970s, the government of Brazil launched the National Fuel Alcohol Program or Proálcool, which aimed at increasing the share of domestically produced fuels in the country's fuel pool. Employing various forms of support, the program proved to be spectacularly successful. By 1980, ethanol had a larger market share in the transportation sector than gasoline (Chart 5).
So much for it's not subsidized.

And yes, it is ongoing:
With the liberalization of hydrous alcohol prices in 1999, government intervention largely stopped. Today, authorities regulate the market through changes in the blending rate for anhydrous alcohol and occasional purchases for or sales from strategic reserves and credits for storing ethanol. At the same time, ethanol enjoys a tax advantage over gasoline.

But perhaps you are right about the US: prices here are artificially high. It's just that in Brazil the are artficially low...

da vinci



Department of Civil and Environmental Engineering, University of California 437 Davis Hall, Berkeley,
CA 94720;

Environment, Development and Sustainability (2005) 7: 319–336 DOI 10.1007/s10668-004-7317-4

Abstract. It is shown here that one burns 1 gallon of gasoline equivalent in fossil fuels to produce
1 gallon of gasoline equivalent as ethanol from corn.

When this corn ethanol is burned as
a gasoline additive or fuel, its use amounts to burning the same amount of fuel twice to drive a
car once.

Therefore, the fuel efficiency of those cars that burn corn ethanol is halved. The widespread
use of corn ethanol will cause manifold damage to air, surface water, soil and aquifers.

The overall energy balance of corn conversion to ethanol demonstrates that 65% of the input
energy is lost during the conversion. Carbon dioxide sequestration by corn is nullified when corn
ethanol is burned, and there will be additional carbon dioxide, nitrous oxides, and sulfur oxide
emissions from the fossil fuels used to produce the ethanol.

PS: what part of the above is not clear ?

The comments to this entry are closed.