July 27, 2005
Pimentel's Biofuel Study Is Bunk
The word is that the study by Cornell's Dr. Pimentel, documented by me here and here, might be worthy of a little mocking. The problem I see, however, is that we have conflict of interest on both sides of the argument.
On the one hand, we have Dr. Pimentel, apparently known for "dissing" biofuels for years, saying that there is a net energy loss, especially when using petroleum, when biofuels are created. Then, on the other hand, we have a pretty good rebuttal from The National Corn Growers Association. The problem with the rebuttal, of course, is that it's from the National Corn Growers Association.
They would stand to gain quite a bit if biofuels took over as the new American energy source, since alot of biofuel, especially ethanol, would be made from corn. Either way, here's what they have to say:
In his recent article, "The Limits of Biomass Energy", Dr. David Pimentel concluded that it takes 1.7 times the energy to produce a gallon of ethanol compared to its energy content. According to a much more detailed analysis by USDA1, this is an incorrect result. Factually, the amount of energy in ethanol compared to the fossil energy used in production is 1.23 to 2.01 times as great. The reasons for the differences are set out in the following note.The Corn Growers Association's Conclusion:
In the estimation of energy utilization, it is important to use the most up to date data. Much of the discrepancy between Pimentel's study and the USDA analysis may be traced to the use of very out-of-date information and incorrect assumptions by Pimentel that leads to the wrong conclusion. The following two examples demonstrate this critique of pimentel's work:
* Agricultural efficiency has improved dramatically in recent times. Since 1980, planted corn acreage has been a nearly constant 73 million acres. The corn yield has increased from 91 bushels per acre to 137 bushels per acre in 2000. During the same time period, the inputs per bushel have declined sharply.
* Pimentel used a 1979 estimate for the energy used to manufacture ethanol of 70,000 BTU/gal. First generation ethanol plants used up to 120,000 BTU/gal of ethanol. In 2000, a state of the art dry mill requires about 38,000 BTU thermal and 1 kw-h (3,413 BTU) electric per gallon.
The 1995 USDA analysis was based upon the best available data at the time and examined corn production and ethanol manufacture on an industry average basis. It acknowledged that ethanol manufacture yields both food and energy and in the most conservative approach, estimated the replacement energy cost for the corn byproducts to establish their worth.Other flaws in Pimentel's study are being pointed out in many places, one being the forum for the well-educated folks over at BioDieselNow.Org. For instance, one poster named "TurboBiodiesel" has this to say:
The Pimentel analysis is based upon older data and data not representative of US average farming practice and US industrial efficiency. Pimentel ignores the fact that ethanol manufacture also produces food.
The USDA analysis clearly shows, contrary to the Pimentel paper, that US farming and ethanol manufacture are very energy efficient, and that the energy content of ethanol delivered to the consumer is significantly larger than the total fossil energy inputs required to produce it. USDA estimates that ethanol facilities produce at least 1.23 units of energy as ethanol for every fossil BTU included considering all energy inputs related to corn farming, corn transport, ethanol production, and distribution and transport of finished ethanol.
One major flaw of Pimentels assertions, is that his studies assign all energy costs to components of the production cycle and do not discount those numbers for other materials produced in the process.More from BioDieselNow.Org here. If this is true, it would certainly make sense. The problem now, however, is that the study's starting to get alot of press, which could spell disaster for the possibility of biofuel becoming the next big energy source.
For example, in his soybean biodiesel chart, he stated that it takes 5,556 kg of soybeans to make 1,000 kg of oil. He assigns all of the energy cost of 7,800,000 keal (don't worry about this number it is a measurement like btu) for growing the soybeans to the soy oil. For an energy cost of $1,117.42 this is 92% of the final energy costs of $1,212.16.
Yet, 82% of those soybeans are reduced to soy meal, which he writes off as "soy byproduct waste". (Now we know better than that) This according to his numbers results in a net energy loss of 32% for the production of the soy biodiesel, because the "soy byproduct wastes" have no assigned energy cost. Yet in his text he allows that one can credit 2.2 million keal to the meal produced which will result in an energy loss for the final product of 8%. However, his posted table of energy inputs for soy do not include any energy credit for the meal.
Now if I were to use his same numbers, yet shift 82% of the energy costs to the soy meal. We would than have a net energy gain for the soy biodiesel of 40%.
Posted by George at July 27, 2005 6:10 AM Category: Alternatives