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MIT Analysis Describes Energy Benefits of Ethanol

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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.




Wait, so any previous analysis of ethanol didn't use Monte Carlo sims? *sigh*

shaun mann

i wonder if they also include the opportunity cost for the land used to grow switch grass.

ie which ends up with less CO2 in the air:

i use land and industrial farming to produce switchgrass, convert it to fuel to drive my car

or i use petrol in my car and cover the land with forest


I'd recommend reading this post as well before formulating opinions about the validity of ethanol as a gasoline replacement. To me, there needs to be a much more compelling return-on-investment in terms of energy than ethanol provides at best, before it can be considered an alternative.



Mature forests are CO2 neutral; only young forests take up more CO2 than they emit.

Rafael Seidl

If you consume just about as much fossil energy producing corn ethanol than you get out, the total amount of fossil fuel consumed to drive your car is about the same as driving it on petroleum-derived gasoline to begin with. Far from proving ethanol's energy benefits, Ms. Goode's research actually supports the argument that the CAFE loophole for E85-capable FFVs is a complete crock for first-gen corn-based bioethanol.

Other feedstocks, including sugarcane and nipah palm grown in tropical latitudes, deliver a far better energy balance but obviously do nothing for American farmers or the politicians they vote for. There is still a $0.54 import tariff on ethanol. Cellulosic ethanol promises much improved EROEI as well, without the risk of promoting clear-cutting of tropical forests.

The numbers for first-gen biodiesel are a little better but there, too, there is still plenty of room for improvement (e.g. via algal oil).

Biogas is much easier to produce from biomass; after scrubbing, it is suitable for use in spark ignition engines or indeed, home heating furnaces etc. Any comprehensive evaluation of the economics of biofuels should therefore include CNG vehicles running on blends of natural and biogas. Naturally, these are restricted to areas that already feature a gas distribution infrastructure.

Mark A

What would a Katrina style weather disaster, wet or dry, do to these numbers and the availibility of ethanol year around. Remember corn has a limited growing period window. It will not grow under snow.

If you consume just about as much fossil energy producing corn ethanol than you get out, the total amount of fossil fuel consumed to drive your car is about the same as driving it on petroleum-derived gasoline to begin with.

It depends on what your goals are. Because ethanol production uses more coal and natural gas (electrical and boilers), it allows tUS to import less oil. So while in terms of environmental issues and total energy stock issues it may be neutral, corn ethanol does result in a smaller demand for crude, which many think has positive ramifications in foreign policy and the US economy.

I tend to think that ethanol is a little too "hot" right now, but that we'll start to see a gradual shift from corn kernel based ethanol to other feed stocks. The current political willpower is only there because we're talking about corn, so that's what's getting the ball rolling.


Cellulosic ethanol has "promise". It has had "promise" for decades. Is cellulosic ethanol the new nuclear fusion or the new hydrogen?

The title of this article is misleading. The study did not confirm the benefits of ethanol, demonstrating that it's benefits are marginal at best and hardly worth doing unless, of course, you receive massive subidies which is the case at present.

Also, we should not gloss over the systems boundaries issue. I still do not think that anyone has made a convincing case that we should ignore, for example, the energy input contribution of farm equipment. If the farmer was doing financial accounting, he would damn sure include the costs of this farm equipment. So why should the accounting be different in the case of energy inputs?

And how will we make the transition from corn to cellulosic ethanol? Do we eliminate the subsidy for corn and provide it for cellulosic?

From a balance of payments perspective, the use of coal for ethanol is an improvement to the extent that it substitutes for imported petroleum. From a carbon intensity standpoint,however, it is a step backward.

In the mean time, the most egregious feature of this whole ethanol sham is the CAFE standards loophole that the auto companies are getting. Worse, they are mainly using this loophole on their biggest gas guzzlers.

And while we are considering the benefits and costs of ethanol, let us also consider the impact of increased corn costs and reduced food supply.

Even assuming the EROEI of corn ethanol is slightly better than one, considering all the other negative impacts, it is something not worth doing, unless you are receving subsidies or making your CAFE look better. Otherwise, we could just ignore this enterprise as just the folly of a bunch of delusional corn farmers and ethanol investors.

Unfortunately, it is creating the comfortable illusion amongst politicians and consumers that we can continue easy motoring without having to cut back one iota from our wasteful ways.

If my energy return from farming was equal to ethanol, I would be dead or at least in extreme poverty very quickly unless, of course, I had an outside source of income.


I think a lot of the energy may be in nitrogen fertilizer. The natural gas used to make it is considerable. If they used gasified biomass like corn stover to get the H2 to make the fertilizer, the energy balance might be better. While you are at it, use the syngas to make CNG to make the ethanol.

fyi CO2

"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."

This came from MIT?
Defining the problem accurately with information available today is what makes an analysis valid.
"One assumption is that the availability of that feed will enable traditional feed manufacturers to produce less, saving energy"
An analysis would validate/invalidate this assumption - is this occurring today?

If E85 from corn is a stepping stone, let us not allow this subsidized/loopholed pebble to trip us up in pursuit of global sustainability which requires consumption control (carbon tax).


The EROEI, of corn C2H5OH, is in a tug of war between increasing demand reaching into more energy intensive feedstock, and improved technology. As the number/capacity of ethanol plants rapidly expands, they take up cheaper feedstock first (non-irrigated corn on rich farmland), then move onto corn from drier, less productive land. This puts a negative trend on the energy balance. OTOH, better technology improves the yields per acre/bushel/ton water/fertilizer. All the while, the demand for corn goes up, inducing fierce competition among processed foods, livestock, and ethanol operations. Exports may also sink, and may generate an interesting dynamic of increased export commodity prices for third world farmers.


"This research was supported by BP America." Interesting...Is this part of an alternative fuel fact find mission assigned to BP by the predatory American Oil Cartel? Don't laugh, it could very well be the truth. The sooner you realize that these companies must continue to control all the forms of energy to stay profitable, the closer to the truth you get.


The boundaries of the study are indeed important.

The reason? Because the USA grows most of its corn for livestock feed purposes.

Therefore it makes (some) sense to process this animal feed to extract vehicle fuel prior to giving it to the livestock.

Even if there were no ethanol plants farmers would continue to use vast amounts of energy to produce this corn.

So the question(s) really become:

How much EXTRA corn will be grown to make up for the loss in volume of livestock feed as corn kernels are turned into DDG. (and how much extra fertiliser and other soil conditioners will be needed)

How much EXTRA energy is used by all the new ethanol plants for distillation.

I suspect that the answer to the above questions is quite a bit less than the energy obtained in ethanol.

So looking at the system with the attitude that the bulk of the energy consumption would exist anyway, ethanol does begin to look like a better deal.

Does anyone truly believe that if all ethanol plants were shut down tommorrow that corn production would cease? Of course not. Of course the 64million dollar question would be "how much would corn prices fall & how would that affect next years planted acreage"

Remember the corn industy is a livestock feed production game with a little fuel production skimming off the top.



The BP disclosure should cement the doubt. Curious too that there is little about the century of energy inputs to build the petroleum infrastructure. Costs of drilling (onshore, offshore, slants, five mile, etc.) refinery, e-disaster cleanup, Superfunds, aging refineries, long distance transport, conflict costs (two World Wars, two Iraq wars, Middle East unrest) environmental impacts, health impacts, loss of alternative business economies, etc. etc.

I'd like to see a non-oil industry study. Shame on MIT for not going the distance to consider their sponsor's "variables."

tom deplume

I wonder if the best way to turn cellulose into motor fuel would be to burn it in a boiler to generate electricty to charge EV batteries?


Studies showing tobacco was not harmful or addictive were common 50 years ago. These studies were full of endorsements by real doctors and various experts. Some even claimed smoking was healthy. Celebrity endorsements were the rule. Tobacco production was even subsidized at the state and federal levels.

Eventually people figured out these studies were directly or indirectly funded by big tobacco and related interests. Today, we may marvel at how foolish people must have been to believe any of that nonsense yet people continue to accept the propaganda of big oil.

The fact is the oil industry is the most heavily subsidized industry in the US. They are a huge sinkhole of public money and manipulators of public policy. Petrochemicals are also known carcinogens.

The ethanol price in the US is artifically high (not low!) due to heavy taxes. Worldwide prices of ethanol are less than $1/gal with no subsidies. In 2005 ethanol hit $0.45/gal while gas was topping $3/gal. What's happened in the US is the large oil companies and the largest agribiz companies (ADM, etc) have colluded to keep prices high.


MrX, correct. It is, after all one of nature's most simple activities: plant biomass to sugars to alcohol. People have been making this stuff in the backyard for hundreds of years out of nearly anything that grows.

Only slightly off topic is a UN FA study that shows the destructive effect of cattle farming responsible for approx. 9% of CO2 generated by human activity.

"Livestock now use 30 percent of the earth’s entire land surface, mostly permanent pasture but also including 33 percent of the global arable land used to produce feed for livestock."


Last time I looked, ethanol was about $1.50 per gallon wholesale, you get 2 1/2 gallons of ethanol per bushel and a bushel costs about $3. So if the feed stock costs $1 per gallon, I don't see the price at $.50 as quoted. I would guess that most of the energy is in the processing of ethanol. Boiling the mash and distilling the ethanol. Since water comes with the distill and that is unavoidable, you have to put it through membrances that have a lot of pumping costs. So you have lots of electricity and heat. They get the heat from coal or natural gas. We could run our cars on NG and turn the coal to fuel with CTL or as some have pointed out IGCC and BEVs. The fact of the matter is then, you have the energy costs whether you use cellulose or corn. It would be nice to see a study of the costs of gasification of the cellose instead of distill. I have several in my computer and there are several on this site that say it is twice the yeild from a ton, but I have not seen the energy balance yet.

An Engineer

I suspect you have been drinking this stuff. Take a nap, then call us back. Alternatively, please produce some proof of ethanol @ $0.45/gal. Or explain what taxes you mean. And while you're at it, don't forget to subtract the subsidies Uncle Sam so generously shower on corn producers. At the prices you mention, Brazilian ethanol would be flooding the US market, even with the current tariff, only $0.54/gal, making imported ethanol a no-brainer at a mere $0.99/gal.

Sorry guys, this is not a big conspiracy by Big Oil: it is an assault on common sense by politicians with narrow self-interest their only goal. They are aided, of course, by the mainstream media ("Cut to the car chase!"). Assuming we pull out of it at some point, the stupidity of today will amaze generations of historians for centuries to come.

Roger Pham

Corn ethanol is already a loss cause for transportation fuel, scientifically speaking.
I move that we should all have a party and drink all those moonshines, Scotch, Jack Daniels or Jimmy Beam...your choice, ...and in the mornin'...*burp* (after the hang over)... figure out a way to urge Congress into considering turning waste biomass into biogas or H2 for transportation. This is the only quick way to achieve energy security AND to reduce global warming!


Everybody else in the world uses sugar to make ethanol. Which is why everybody else in the world pays so much less for ethanol than we do in the US.

It's not just taxes, it's quotas. There's limits on what you can import.

For the record, I don't support E85 because it requires new pumps and cars. E10 in all gas is a more efficient deployment. Ethanol supports a higher compression ratio too, which means more power from a smaller lighter engine. And while the milage is worse the exhaust is less toxic.

Biodiesel is actually better in most ways and the mix there can go to B80 and still run in existing pumps and cars.

An Engineer

Make that converting biomass (waste) into liquid fuels (no changes to existing vehicles or fuel pumps) and I'm in.

Did you perhaps mean to say $0.45/liter or $1.70/gal? Perhaps that is a big part of the problem in the US: you can't develop the fuels of the future using Queen Victoria's units of measurement...


You ask why we pay so much for sugar. Maybe this will explain some of it.


Nah Engineer, please check the link.

The production price of the sugar used in Brazil was less than $0.08 a liter and it's not subsidized.

Pint o Shine is right but the sugar politics in the US actually go back to the war of 1812 and restrictions on ethanol production go back to 1791, right before the Whiskey Rebellion. Showing that history repeats itself, large producers only had to pay 6 cents a gallon on credit while small producers had to pay 9 cents and in cash only at a time when many farms had little or no hard coinage.

The government makes a big deal of how the farmers just wanted to get drunk but in reality alot of that alcohol was for lamps because the whale oil cartel from new england charged very high prices for their lamp oil which doesn't burn as clean.


I'll be putting my money on the Fischer-Tropsch CTL process for the future in the USA. Clean, efficient, lots of reserves, any carborous feed stock, and generates the same liquids we are used to. It's not that green using coal or natural gas for feedstock but itis with cellulose, lignin and other feeds such as animal and human waste.
It would be an alternative way to dispose of old tires.
The primary use of the producer gas could be to generate clean electricity during peak demand and liquid fuels during off peak. I'll be watching this technology.

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