About that ethanol study …

Courtesy U. of Minnesota

Exit up ahead: A University of Minnesota study has concluded that corn-based ethanol is no better than gasoline.

The Star Tribune says ethanol may even be a bigger polluter, when it comes to greenhouse gas emissions and particulate matter. Cellulosic ethanol made from switchgrass and other plant materials is far better for human health, the scientists say.

But the Renewable Fuels Association claims the study is flawed. Among other things, it assumes that grassland will be taken out of the federal Conservation Reserve Program to make more corn-based ethanol. The RFA says most of the increase in corn production in the U.S. has been through higher yields rather than conversion, and there’s no peer-reviewed evidence for the study’s methods. (see the pdf).

Who to believe? The study has been peer-reviewed and published in the Proceedings of the National Academy of Sciences. Here’s the full text (also in pdf).

The scientists note that “Our results show that the proposed methods of producing cellulosic ethanol we consider have lower (greenhouse gas) emissions than corn ethanol or gasoline, consistent with published findings.”

As noted by Autobloggreen, “The study calculated the total environmental and health costs of making each type of fuel. A gallon of gasoline was about 71 cents, compared with between 72 cents and $1.45 for corn-based ethanol and 19 to 32 cents for cellulosic ethanol, depending, of course, on the technology and type of plants used.”

The RFA is the major lobbying group for the ethanol industry, now dominated by corn, and its members include Archer Daniels Midland. Deere & Company, DuPont and Monsanto.

The study can take nothing away from corn ethanol. The alternative fuel has had a positive impact on the U.S., proving that foreign oil isn’t the only way to power our world.

But the findings suggest once again that the road to energy independence runs to the highway of cellulosic ethanol and other next-generation biofuels.

Have any Question or Comment?

8 comments on “About that ethanol study …

Tom Saidak

There are a lot of studies out there, and so I may have missed one or two……

The biggest problem with ANY studies about alternative fuels and their impacts is that they usually use a figure based on “per gallon”. This is TOTALLY misleading. It needs to be based on “per mile traveled”.

I own a Prius, and so I will use that as my n=1 study comparison, and I will use simple numbers, NOT the real numbers to illustrate my point.

During the summer, here in San Jose, California, I can hit about 48 mpg with straight gasoline. In the winter, this drops to 40 mpg. When I talked to my Toyota dealership about this, the first words out of their mouths was “winter gasoline”. In California, during the winter, ethanol is added to the gasoline to “oxygenate” it, so it burns cleaner. I honestly do not know the percentage, but it is much less than 15%. It has a devastating impact on my mpg rating, which is why it drops to 40 mpg, city driving.

So, during the summer, 0% ethanol, I hit 48 mpg. For simplicities sake, let’s assume I have a CO emissions rate of 100 ppm. During the winter months, ethanol is added to the gasoline, and my Prius CO emissions drop 14% (as per the citations here), so I have an emissions rating of 86 ppm. That’s great, right?

Well, no, it isn’t actually. Because my mpg drops to 40, so to drive 480 miles, I now have to buy 12 gallons – not the 10 gallons I would use in the summer. So let us do the math….

Distance = 480 miles

Summer, 48 mpg, 100 ppm, = 10 gal x 100 = 1000 total CO.

Winter, 40 mpg, 86 ppm, = 12 gal x 86 = 1032 total CO.

While my ppm/gallon has dropped 14% (YAY!), my ppm/480 miles TRAVELED has increased 3.2% (BOO!).

The other way for error is seasonal. The EPA can take measurements during different seasons, and see drops because in winter, many of us drive LESS.

The upshot is that ANY study that does not use “per mile traveled” is misleading. It does NOT tell the whole story. Ethanol has only 75% the energy of the same volume of gasoline. It you use a “mpg” rating, it does not show the difference based on the fact you have to buy 33% MORE fuel to cover the same distance.


@ Tom: Typically, all peer-reviewed studies in this industry use an energy conversion factor for ethanol representing its ‘gallons of gasoline equivalent’. When you read the study’s conclusions quoted in ‘per gallon’ terms, they’re referring to gasoline-equivalent gallons – so your personal experience and concerns are accounted for here. The U Minnesota team states this on the first page of their study.

For general consumption:

As in every study of this nature, the output is only as good as the input. I won’t nit-pick their study because I’m not part of the academic community. But I’ve been working in the biofuels industry and believe some of their assumptions to be unrealistic (for both corn-based and cellulosic ethanol). My experience holds that the team’s “advanced” corn ethanol is probably the appropriate scenario for today’s ethanol production. That scenario still doesn’t paint corn ethanol with the cleanest brush, but it’s not quite as negative as their conclusion suggests. Their study should be treated as another data point in the debate, as should other congruent and conflicting studies.

First-generation biofuels are just that – our first best shot at making an alternative transportation fuel work. Each successive iteration of these fuels incorporates advancing technologies and compounds our experience with the processes, which leads to better yields and more efficient production in the future. Next-generation biofuels will stand on the shoulders of the proverbial biofuel giants that came before them. Let’s be clear that even second- and third-generation biofuels have their challenges. While biofuels are not a panacea for our petroleum addiction, they will help displace petroleum demand and lower overall emissions as a critical holding in our portfolio of energy solutions.


So 10 percent ethanol cut your mileage by 16.7 percent? 48 mpg down to 40 mpg.

So you’re saying that not only did you get absolutely no power from ethanol at all, but ethanol actually took power away from your gasoline? You say ethanol has 75 percent of the energy of gasoline, but based on your stated mileage loss, ethanol in fact has negative energy. I know that’s not true.

If you were using more than 10 percent ethanol, then your gas station was breaking EPA regulations. In truth, I think your mechanic didn’t know what else to say, and ethanol was the easy scapegoat.

Tom Saidak

I initially started my response thinking that the use of gasoline equivalents was a good answer, and I could relax. Then I started my response to crsh and his/her response that I was scapegoating ethanol. By the time I got through with my initial response, I realized that no, I was right to insist on measurements based on miles travelled.

IF we were discussing 1960’s or even 1970’s vehicles, this discussion would be moot, and needless. Since the 1990’s, and possibly earlier, vehicle engines have been using computer chips to manage the engine. These chips use algorithms that do NOT take “winter gasoline” into account. From reports and articles in the early 1990’s when I bought my 1993 Geo Metro, I became interested in this technology. Nowhere, have I heard of a sensor that can tell the computer chip to switch to a gasoline/ethanol blend algorithm.

My Prius is an extreme example of how this algorithm plays out. The first part of the algorithm is temperature based. As per my manual, the computer chips will NOT use the high mileage algorithm until the engine reaches a particular temperature (what exactly that is, my owner’s manual is not forthcoming). IF I burn a lower BTU per volume fuel, then it will take longer to reach that temperature. This means that my Prius will NOT shut down the engine on idles lasting longer than 3 seconds, until that temperature is reached. I do not know that the red lights in San Jose, California run longer than any other city, but I swear that with just 3 red lights per day, one way, I could finish War and Peace in a month at the most, but I digress. With longer idle times, my Prius is going to suffer a major mpg loss of at least 4 mpg. How do I know this? Check out the Honda Civic hybrid, which does NOT ever shut down. The Civic Hybrid is rated at 40/44 mpg (highway/city) while the Prius gets 45/48 mpg. Nor am I alone in this – http://townhall-talk.edmunds.com/direct/view/.ef7c05b. As per the post, I lose at least 10%. A blog on Geo Metros shows a similar problem at http://www.automotiveforums.com/vbulletin/t664480.html – check out response #2.

The upshot of this should NOT be seen as scapegoating ethanol. It should be seen as pointing out that this is ultimately a multifaceted, complex issue. As a statistical scientist, equivalency is meaningless unless it can be demonstrated to be universal. The ONLY universal measurement is per mile, and nothing short of that can purport to truly “tell the truth”. The use of non universal algorithms in computer chips means that a realistic look at the synergy requires a vehicle by vehicle approach. The only way to get around this fact is to nail it down by per mile. Otherwise we are comparing apples to onions to potatoes.

This is a complex argument that I have chosen to simplify down to one page. If we want to discuss this at length, we need an appropriate venue, and I am not sure this is the place. I am open to suggestions.

Meanwhile, Keith, I noticed you could reduce url’s to a small phrase – can you teach me that trick or tell me where to go to learn it? Thanks ahead of time!


Perhaps it’s more complicated than this, but my understanding has always been that 1 gallon gasoline equivalent means the amount required to get you the same miles as 1 gallon of gasoline. Apples to apples.

For emissions studies then, it does, in fact, compare the emissions from traveling one mile on ethanol vs. one mile on gasoline. Not emissions from one gallon of ethanol vs. one gallon of gasoline.

And I still don’t see how adding ethanol not only provides 0 energy itself, but actually removes energy from the remaining 90% gasoline. I’ve seen studies that average it at 3-4 percent, some down at 1-2 percent.

Tom Saidak

Traditionally, equivalencies refer to btu to btu ratings. NOT based on travel. Thermochemically speaking, you are correct. The complicating factor is that our modern engines are often run by a computer. The computer has to be programmed. The programming is set for “summer” gasoline – NOT winter gasoline. It would be interesting to see how so called “flex fuel” engines behave. Flex fuel engines have sensors my Prius lacks to determine what fuel they are running.

The only other way I can think of to explain this is that my Prius computer is stupid. It thinks there is only one kind of fuel – 100% gasoline. It thinks E90 is the same as 100% gasoline, and thus doesn’t change what it does. When E90 doesn’t deliver the same energy to turn over the generator or heat the engine up, it steps up to higher settings that are probably unnecessary, and burns more fuel to cover the same miles.

Beyond that, the only other thing I can add is that this affects high mpg rated vehicles more such as hybrids and Geo Metros then low mpg rated vehicles such as the Hummer. And again, this is due to the use of computers to run the engines – not the simple thermodynamics of the fuel.

Tom Saidak

From MIT in today’s email version of their Magazone – http://www.technologyreview.com/energy/22198/?nlid=1789. Check out the 2nd paragraph.

California gasoline is 5.7% ethanol year round. 5.7% ethanol is what is added to reach an oxygen content of 2%. The oxygenate requirement was dropped at the federal level a couple of years ago but California has chosen to continue using the same level until the end of this year when the amount of ethanol required goes to 10%.

Winter blend gasoline has less BTU than summer blend gasoline whether or not it has ethanol in it. The EPA published a report some time back that details the BTU variations between summer and winter blends.

According to the EPA summer gasoline varies from 113,000 BTU per gallon to 117,000 BTU per gallon. That is a difference of 3.4%. Winter gasoline varies from 108,500 BTU to 114,000 BTU. That is a difference of 4.8%.

So gasoline itself varies quite a bit in BTU even within the same seasonal blend. And since blending ethanol with gasoline increases the octane rating, if you are comparing 100% gasoline to ethanol blended gasoline of the same octane rating, then the base gasoline has to be different. So if the base gasoline is different how much of the mileage loss is due to the gasoline and how much is due to the ethanol?

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