I have received several comments about my post About Ethanol questioning whether ethanol had a net energy value (NEV) greater than one, meaning that there was more energy in the ethanol than the energy that was used in producing it. I had not done enough research at that point to have a firm opinion, although I tended to agree with those who believed the NEV was greater than one and I still believe that it is. But, I have come to the conclusion that NEV is not the right criteria on which to judge the energy content of ethanol. I agree with Dr Wang of Argonne National Laboratory, summary of paper, who argues that the proper criteria is: 1) to calculate the amount energy that it takes to make ethanol and compare it to the energy required to make the product that you wish to compare it to and 2) compare the amount of petroleum energy that is used to produce the two fuels. He found that it takes 1.66 times more energy to produce gasoline than it does to produce ethanol. Don't get fooled by his inclusion of solar energy in his total energy chart, it is "free" and including it only confuses the issue. The amount of petroleum energy used in making ethanol is very small, making a very efficient means of transforming a small amount of petroleum into much larger amount of non-petroleum fuel.
Two camps developed, one claiming that the NEV for ethanol is greater than one and the other saying that it is less than one. The trouble comes in defining the values of energy that should be used and what energy inputs are relevant.
Another concern with ethanol is that it takes up too much land. This would be true if we had to rely on corn kernels to produce the ethanol. When enzymes are developed and we can process cellulose into ethanol, we can produce ethanol using much less land because the whole corn plant, known as corn stover can be used. Enzyme development is nearing commercialization. Novazyme has demonstrated a low cost enzyme in the laboratory and Iogene has a pilot plant operating using their enzyme. Corn stover probably will be used initially with enzymes, followed by using better sources of cellulose, such as switchgrass, waste wood products or trees which require even less land and can be produced on marginal land. If municipal waste is used, no new land will be required. The biorefinery may be a future development to produce gasoline and diesel, as well as chemical feedstocks and electricity.
Producing a fuel at a competitive cost, without subsidies, is another test that a fuel must pass. Almost all fuels receive a subsidy, including petroleum and that makes establishing the true cost difficult. Ethanol is approaching the point that it can be produced competitively without direct subsidies, although the growers may still receive a farm subsidy of some sort. Using cellulosic feedstock, with cost effective enzyme hydrolysis of the cellulose into sugars, should make it competitive cost wise as well as consuming much less fossil energy.
My conclusion is that while Patzek and Pimento have determined the energy consumed in the total ethanol cycle as they have defined it, it is not a useful method of analyzing the problem. If they want to do a study, that is used to determine what fuel is most energy efficient, they should do an analysis comparing similarly defined competing cycles, such as the ethanol cycle to the gasoline cycle. (Believe it or not, I wrote the essence of the last sentence before I had come across the Wang paper) My conclusion was partially based on the following table which is taken from "Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus,", May 1998 which gives a comparison of energy efficiency of four liquid fuels.
Summary - Energy Balance/Energy Life Cycle Inventory
|Fuel||Energy Yield||Net Energy (loss) or gain|
The ratio of the energy efficiencies of two fuels can be calculated using the ratio of the NEV values(energy yield in the above table). I used the fuel with the largest NEV as the numerator for consistency, which gives a value of 1.66, coincidental the same value that Wang calculated.
In computing the energy input to a fuel, all the energies required to produce the commodity must be included. For corn that would include the energy for planting and cultivation, the energy to produce fertilizer and herbicides, the energy to produce the seed corn, the energy to transport the corn to the ethanol plant, etc. To this must be added the energy to convert the corn to ethanol with credits for byproducts and the energy to transport the ethanol to refueling stations. The total energy for gasoline includes energy for petroleum recovery (taking it out of the ground), transportation to the refinery, petroleum refining with credits for other products produced and transportation to the end user.
Wang also showed that the preponderance of recent studies have shown that the NEV of ethanol is positive. Only Pimentel (with Patzek sometimes) has found the NEV to be negative and they have been widely refuted for using incorrect information and including spurious amounts of energy. Wang's chart also shows the upward trend of NEV values over the past 17 years.
The most widely published detractors, Dr Patzek from UC Berkley and Dr Pimentel from Cornell have published several papers on the energy content of ethanol, the latest paper dated March 24, 2005, claims that the energy consumed in producing ethanol is six times more than it delivered. It defines the theoretical basis for their methodology, making the audience for the paper primarily scientists and engineers which makes it hard to follow by most of the general public. I guess that's OK, but it doesn't help their cause.
They include the energy required to feed the manpower, which I find ridiculous in that these people would have to be fed whether or not they worked in farming or the ethanol plant.
They do not assume a digester to treat the process water within the ethanol plant, which is used in state of the art plants. The digester eliminates external waste water treatment and produces biogas that can be used in the plant either to produce electricity or to partially or totally reduce the consumption of natural gas.
They include the inefficiency of the car engine that burns the ethanol, which I don't think should be included, as it has nothing to do with the production of ethanol. The energy content of ethanol is less than that of gasoline. To take that into account they should have calculated the amount of methanol required to produce the same energy as a unit quantity of gasoline. Furthermore ethanol is being used as a blending stock in gasoline and is likely to be used that way for some time, so this has to factored into the equation. They are using today's technology to produce ethanol not some future technology that might be used to produce ethanol as a 100% fuel in the future and is likely to be more efficient.
They also include the energy in the fossil fuel that is used to create the electricity. I believe that including this energy, which is predominantly coal, and is accurate theoretically, should be considered in a different way as Wang has suggested. This energy is derived from a source other than a liquid fuel, which we desperately need to operate our transportation vehicles and conserve oil for other purposes. Quoting from Dr Graboskie of the Colorado School of Mines "In producing ethanol from corn, wastes and energy crops, low-grade fuels like coal and natural gas are effectively transformed into high-quality liquid transportation fuels. About 84% of the energy consumed in producing corn-based ethanol comes from coal and natural gas, while only 16% is petroleum based. Thus, corn ethanol represents a very efficient way of increasing U.S. gasoline and diesel supply. Because of increased supply, ethanol acts to depress the price of gasoline and fuel oil."
In a 2001 paper Graboskie, refuted an analysis by Pimento. Researchers at Argonne National Laboratories found that the energy in corn was 1.37 times the energy in fossil inputs. The USDA found the NEV to be 1.24. According to Graboskie, Pimental used erroneous values for the energy required to produce fertilizer. He overstated the energy requirements for corn production by assuming that all corn is irrigated but that the yield per acre is the national average rather than the 75% higher yield for irrigated corn. They have corrected the energy required for seed corn and irrigation but still have a disagreement on the energy required to produce fertilizer. AlterNet has several good discussions on the merits of ethanol.
We have or can build enough coal, hydro and wind power plants to produce electricity. The coal plants, which predominate, can be clean coal power plants, which have been demonstrated and should eventually be used in new power plants. Existing power plants can be retrofitted if necessary to reduce pollution to acceptable limits. We have enough coal to last for 100-200 years if we don't use it on wastefull boondoggles. The better way to do get our electricity is from solar energy (which includes wind and wave power) and nuclear power. Unfortunately photovoltaic's are far from economical now. Concentrating solar power is a lot closer to being competitive. Nuclear is considered unacceptable by the majority of U.S. citizen.
Advanced clean coal plants should used a combined cycle (IGCC) which could nearly double their efficiency. CO2 emissions are inversely proportional to efficiency. Efforts to demonstrate this technology should be increased to enable implementation of this technology at the earliest time possible in order to conserve our coal resources. Sequestration of CO2 is planned in future plants, but should be demonstrated now at a large scale using geological sequestration. It should be able to be retrofitted on some plants, depending on their geographical location, but not easily to all existing plants. Other means of sequestration are being developed for use in other locations. Siting of new plants should only be allowed at locations where sequestration is possible. Hopefully we will be able to economically produce electricity from solar power and fusion power in the future. Detractors cite that producing ethanol uses up our fossil fuel resources. That it does, but at a much lower rate than other alternatives. Our solar technologies which use less fossil fuels in their life-cycle, are not developed enough at this time to make a significant impact. As far as I am concerned we have no choice at this time to use biomass, wind and coal as our primary sources of energy, conserving petroleum and natural gas for only uses where we have no alternatives.
An important fact that I came across is that hydrogen requires more energy to produce than other choices. Patzek and Pimento said that the fuel cell cycle would be even worse than ethanol. To me this is obvious based on the infrastructure required, the amount of energy required to produce the hydrogen and the inefficiency of the fuel cell. We should reduce work on the hydrogen cycle and put our resources into developing more sustainable energy sources. We need a substitute for liquid fuels and using biomass and to produce them seems to me to be our best way out at this time. Conservation of fuel needs to be maximized. Hybrid cars can be, although some are not, a major advance in conservation, plug in hybrids would be even better. Fuel efficiency standards for cars must be instituted, we cannot wait for supply and demand to create the move to more efficient vehicles, it takes too long, meanwhile our limited resources are being used up. Diesel cars should be encouraged using biodiesel made from more efficient sources; biodiesel from algae, Fischer-Tropsch diesel from biomass and coal liquifaction.
Further discussion on the subject of ethanol energy content can be found in Future Pundit in his post Is Corn Ethanol a Good Energy Source generally siding with the con side of the argument. Green Car Congress has a post Governors Ethanol Coalition Recommends $800M Push on Ethanol Production from Biomass that also discusses the question. In general I do not agree with them, but you can read both sides of the issue if you insist.
NREL has a 2002 presentation, "Ethanol from Celllulosic Materials" which details the processing steps for producing ethanol in greater detail than I did in my post "About Ethanol". A GM presentation,1998 has figures for the potential amount of ethanol that could be produced from biomass.