Ethanol”" Energy balance or a balance of power?

The number one question about ethanol should be “”does it take more energy to produce than we get out of it?”"


The number one question about ethanol should be “”does it take more energy to produce than we get out of it?”"

Here is one of those questions that I can answer with a question, which is “”What answer would you like?”" I cruised the Internet and found answers from “”it takes 1.8 times as much energy to produce the product as one gets out”" to “”it is about 70% energy efficient.”"

The Internet is great because you can find an unbelievable amount of information very quickly and easily. The only problem is you do not know if the information is true or not. Usually, what you find is someone’s version of the truth.

The first thing to remember is that a typical gallon of ethanol contains about 76,000 Btu (British thermal unit) of energy per gallon compared to 115,000 Btu per gallon of straight hydrocarbon gasoline. If you use a fuel containing 10% ethanol, your expected fuel economy will decline about 3.4% just on energy content alone.

The second point is how much energy does it take to produce the ethanol. The best source that I found was a paper by Hosein Shapouri, et. al., of the U.S. Department of Agriculture, titled “”The 2001 Net Energy Balance of Corn-Ethanol.”" This paper seems to use the best science for determining a fact-based answer to the question. In the paper, they calculated that it takes 18,713 Btu to produce the corn, 2,120 for transportation, 49,733 for ethanol conversion, and 1,487 for ethanol distribution. This gives a total energy used of 72,052 Btu per gallon of ethanol produced. When this is compared to the total energy content of a gallon of ethanol ? 76,000 ? we see a positive energy balance of 3,948 Btu per gallon of ethanol produced. This is an energy efficiency of about 5%, or 3.4% if compared to the hydrocarbon fuel it is to replace.

In the paper, the authors state that “”on the average, starch accounts for 66% of the corn kernel weight.”" And since only the starch can be converted to ethanol, they therefore allocate only 66% of the energy to the ethanol. I calculate this would reduce the energy needed to produce a gallon of ethanol to 48,040 Btu, which would be an energy efficiency of 37% based on the ethanol heat content or about 24% based on the hydrocarbon fuel it replaces.

The other problem is that in real world tests I have run, a fuel containing 10% ethanol does not perform as well as a straight hydrocarbon fuel. Based on the energy content, the fuel economy should be only 3.4% less than that experienced with a normal fuel. In the real world, I have always seen at least a 5% drop and, in the winter, even more. Part of this is due to the refiners putting in lower energy components as they adjust for the higher octane of the ethanol.

The bottom line is that I feel that the energy balance for ethanol-containing fuels is basically zero. That is it takes about as much energy to produce the fuel as one can expect to get out.

So is ethanol the answer to the energy crisis and the United State’s dependency on foreign oil? Well, there is the reduction in emissions thing.

Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.

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