by Dale Allen Pfeiffer
The net energy value of biodiesel and ethanol is very hotly debated. There are many net energy studies of biofuels, particularly ethanol, which give a wide range of values. The main problem is that net energy studies are easily influenced by biases. The researcher must choose the energy inputs and outputs and the values to assign to these various inputs and outputs. There is no clear standard. However, in a survey of a large sampling of ethanol studies, the authors found that the average of all these studies taken together showed a net energy loss of 8%. Throwing out the three highest and three lowest outliers cut this loss to 2%. 
In this report, while we will discuss the net energy profile of various biofuels, we will also bring up several other criticisms of biofuels and the biofuel industry that are not so controversial, nor so open to debate.
In researching this report we read a number of studies, including many that gave a very favorable view of biofuel net energy production. We found that the reports most often referred to in support of biofuels (The Energy Balance of Corn Ethanol: an Update, Shapouri, H., et al., 2002; The 2001 Net Energy Balance of Corn Ethanol (preliminary), Shapouri, H. et al., 2005; Fossil Energy Use in the Manufacture of Corn Ethanol, Graboski, Michael S., 2002; Fuel-Cycle Fossil Energy Use and Greenhouse Gas Emissions of Fuel Ethanol Produced from the U.S. Midwestern Corn, Wang, Michael, et al., 1997) left out or grossly underestimated many of the energy inputs. Following Shapouri, many of these positive reports leave out natural gas and electrical inputs altogether. They also tended to give generous energy credits to ethanol byproducts. For these reasons, we have decided not to source these studies.
In this section of our report, we will depend on the following studies: Biodiesel Performance, Costs and Use, Radich, Anthony. EIA, 2004; Thermodynamics of Energy Production from Biomass, Patzek, T. & Pimentel, D., 2005; Thermodynamics of the Corn-Ethanol Biofuel Cycle, Patzek, T., Updated 2005; and Ethanol Production Using Corn, Switchgrass, and Wood; and Biodiesel Production Using Soybean and Sunflower, Pimentel, D. & Patzek, T., 2005. Thermodynamics of Energy Production from Biomass and Thermodynamics of the Corn-Ethanol Biofuel Cycle deserve to be singled out for being particularly enlightening. We have found that these studies seem to be the most thorough analyses available.
While Pimentel and Patzek have been criticized for a bias against biofuel production, we have found numerous examples where they chose to be overly generous to ethanol and biodiesel in their data. The true net energy figures are likely much worse than they report. In Thermodynamics of the Corn-Ethanol Biofuel Cycle, Patzek uses the Shapouri research as the source for much of his data.
Perhaps one of the biggest differences between Pimentel and Patzek and the more positive studies mentioned above is the concept of energy credits. Shapouri, Wang and others maintain that ethanol byproducts (such as dried distillers grain, gluten meal, gluten feed, and whey) are themselves useful products whose market or energy value should be brought into the analysis to help offset the energy costs of ethanol production.
The various byproducts listed above are used as cattle feed. Of these byproducts, dry distillers grain is by far the most abundant, providing the corn is dry milled. As such it replaces soy beans in the cattle diet. Around 3.3 kilograms of dry distillers grain can be derived from 10 kg of corn ethanol feedstock. Dry distillers grain contains 27% protein, in comparison to soybean feed that holds 49% protein.  Soybean production is much more energy efficient than corn production. Because soybeans fix nitrogen, there is no need for the energy expensive nitrogen fertilizers in soybean farming. When this comparison is taken into account, the allowable energy credit for corn byproducts shrinks considerably.
Patzek does not allow ethanol any energy credit from byproducts. He argues persuasively that all ethanol processing leftovers should be returned to the field to help replenish soil humus and microelements. Instead of an energy credit, Patzek offers a cut in fertilizer energy costs if the processing leftovers are returned to the field, minus transportation and disposal costs.
In January 2006, the results of a new study were published in Science.  This study sought to reconcile the differences in seven other studies by feeding them into a common model where all data and assumptions could be adjusted for direct comparison. The studies reviewed were the Graboski (2002) and Shapouri (2002, 2004) studies, the Patzek (updated 2005) and Pimentel & Patzek (2005) studies, and two other studies not mentioned above: The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model, version 1.6, Wang, Michael, 2005; and Ethanol as Fuel: Energy, Carbon Dioxide Balances, and Ecological Footprint, Dias de Oliveira, Marcelo E., et al. (2005).
Farrell et al. concluded that, in the best case scenario, ethanol production had a much better net energy profile than gasoline. However, this author questions this conclusion and many of the assumptions of Farrell et al. The Farrell et al. study found fault with Patzek and Pimentel for not incorporating energy credits without answering their argument as to why energy credits should not be allowed. In fact, the authors of this new study suggest that increased ethanol production will lead to more byproducts which will in turn be substituted for soybeans in animal feed. This entire argument seems to run false if they will not address the matters of corn byproducts versus soymeal and recycling of all byproducts back into the fields.
The new study also rejects all labor costs, and suggests that the values of energy embedded in farm and ethanol plant machinery as used by Patzek and Pimentel are too great by an order of magnitude. The new study does incorporate effluent processing energy, but the figures they use for remediation seem unrealistically low.
In any case, even after applying all of these adjustments and more, this new study does not succeed in moving Patzek and Pimentels reported net energy figures into the positive. The net energy value for corn-ethanol in Patzek (updated 2005) moves from about -5 MegaJoules/Liter (MJ/L) to around -2 MJ/L. The net energy value in Pimentel & Patzek (2005) moves from less than -6 MJ/L to around -4 MJ/L. None of the figures from the various studies examined move very significantly.
Net energy as a function of Net ethanol production and net petroleum
Graphs taken from Ethanol can Contribute to Energy and Environmental Goals,
Farrell, Alexander E., et al. Science, vol. 311, January 27th, 2006.
In the end, this new report does not really say anything new, and it is obvious that the authors ignored the Patzek and Pimentel studies in drawing their conclusions. By allowing for energy credits and other adjustments favorable to ethanol, this new study only serves to reinforce Patzek and Pimentels analysis that ethanol production is an energy loser. It is doubtful that this debate will be resolved any time soon. For this report, we will utilize the reports listed above and then move on to the other criticisms of biofuel production.
Patzek has responded to Farrell et al. with a paper demonstrating that Farrell et al.s net energy study of the corn ethanol cycle did not define the boundaries of the system under study, conserve mass as necessary under the Laws of Thermodynamics, or conserve energy as required by the Laws of Thermodynamics.  Dr. Patzek notes that these errors render the entire report and all conclusions drawn from their model null and void. What Farrell et al. have done is to create a perpetual energy machine, which of course cannot exist in the real world due to the Laws of Thermodynamics.
Biodiesel from Yellow Grease
Yellow grease is the term used for any recycled cooking oil. As such, it is nearly impossible to do a net energy analysis. We can only give a very partial energy analysis of the generation of biodiesel from yellow grease. The production process uses, per gallon of biodiesel, 0.083 kilowatt hours of electricity and 38,300 Btus of natural gas. Given the dollar values of 2002, the EIA estimated energy costs at 18¢ per gallon in 2004, and 16¢ per gallon in 2005 and 2006.  Unfortunately, the unforeseen rise in oil and natural gas prices has raised the energy costs of biodiesel production from yellow grease beyond the EIA projection.
The most common method of producing biodiesel is to react animal fat or vegetable oil with methanol in the presence of sodium hydroxide. Most commercial methanol today is produced from natural gas feedstock, further raising the fossil fuel costs of biodiesel production.
From 1993 to 1998, an average of 2.633 billion pounds of yellow grease was produced annually in the US. That is enough to make 344 million gallons of biodiesel per year, or 22,440 barrels per day. There are, however, competing uses for yellow grease, and so the EIA limits biodiesel production from yellow grease to 100 million gallons per year, or 6,523 barrels per day.  For this reason alone, biodiesel from yellow grease will never be more than a fringe fuel.
A new biodiesel plant costs approximately $1.04 per annual gallon of capacity. Taking into account equity financing and treating the future income stream as an annuity, the EIA places the annual capital cost of the plant at $1.36 million (in 2002 dollars). This equates to 13.6¢ per gallon at full capacity. Operating expenses are estimated to be 31¢ per gallon, excluding the cost of oil or energy. 
It is believed that biodiesel production just manages to cover production costs with a slim profit.  While some economists assume that rising oil and natural gas prices will make biodiesel more competitive, it will also raise the energy costs of producing biodiesel.
There are other problems with biodiesel that are worth noting here. All biodiesel performs badly in cold weather, but biodiesel derived from yellow grease is the worst in this regard. In cold weather, biodiesel forms wax crystals that will clog fuel lines and filters. And as the temperature drops further, biodiesel will become a gel that cannot be pumped. 
This is an important consideration when performing a net energy analysis of biodiesel derived from tropical tree plantations. The energy costs for the nutrient inputs are very high, and the output of the plantations tends to diminish rapidly. Moreover, among biodiesel advocates there is much talk of generating biodiesel from plant trash. Such talk is ignorant, whether this ignorance is willful or merely uninformed. There is no such thing as plant trash, particularly in a tropical forest. We will discuss this at greater length later; but for now, let us simply state that all unharvested plant matter and byproducts should be returned to the ground. If this is not done, then the nutrients lost in this plant trash will have to be replaced from fossil fuel derived sources at a growing energy cost.
The gross heating value of hardwood averages 19.73 ± 0.98 MJ/kg. However, not all of this is useful heat. Much heat is lost to the vaporization of water content. This loss amounts to about 1.4 MJ/kg. Acacia trees have a very high water content, up to 250% moisture content in the inner heartwood. Eucalypts have a lower water content, around 34% to 103%.  Both acacias and eucalypts are extremely thirsty, as are most fast growing tree species. Eucalypts have been used to dry up marshlands because their extremely high evapotranspiration  rate.
Moisture content can be reduced to 10% - 25% through drying, but this is a very energy-intensive process that cuts into the woods net energy. Given time, sun drying can be very effective. However, it is virtually impossible to do with the volumes of wood produced in an industrial-scale plantation. In commercial practices, wood is steam dried. The energy used can be provided from natural gas, coal, electricity, or (as would be most common in remote areas) biowaste.
For the purposes of producing biofuel, wood must be reduced to wood pellets. The process of producing dry wood pellets is the single largest energy expense of the wood-to-fuel industry. The energy required to produce wood pellets is approximately 16 MJ/kg. The transformation of raw wood into pellets requires fully 80% of the energy contained in oven-dry hardwood. When wood pellets are produced as a byproduct of paper pulp or timber production, this loss can be tolerated. But for a wood-to-energy industry 4 kg of wood must be burned to produce 1 kg of pellets (taking into account the volume loss from raw wood to wood pellets). 
If these pellets are burned directly in an electricity generating station, from 1 kg of 10%-wet wood pellets an efficient power station would produce a maximum of 5.59 MJ/kg of electricity. For the production of diesel fuel from wood using a combined fuel/electricity cycle and the Fischer-Tropsch (FT) process, 1 kg of 10%-wet wood pellets would produce a maximum of 2.39 MJ/kg in shaft work (given a 35% efficient car) and 2.34 MJ/kg of electricity. Yielding a total of 4.73 MJ/kg pellets. For the production of ethanol from wood, given that all process energy is provided from the unused components of the wood pellets, 1 kg of 10%-dry wood pellets would produce 1.87 MJ/kg of shaft work (in a 35% efficient car).  For comparison purposes, this data is summarized in the table below.
|Energy Production from 1 kg 10%-Wet Wood Pellets|
|Energy Form||Amount of Energy Produced|
|wood-burning power station||5.59 MJ/kg|
|FT diesel & electricity||4.73 MJ/kg|
|ethanol production||1.87 MJ/kg|
Now we must consider the minimum restoration work necessary to maintain the plantation and transport the wood and pellets. Items that must be considered here are the production of fertilizers, herbicides, insecticides, electricity to grind the wood and produce pellets, heat to dry the wood, and fuel to run the plantation and transport the wood and pellets. As the inputs vary for acacia and eucalypt plantations, we consider them eparately.
For an acacia plantation, the total restoration work is 153 GigaJoules per hectare per year (GJ/ha-yr). A prolific acacia plantation can produce 109 GJ/ha-yr of electricity, 92 GJ/ha-yr of FT diesel fuel/car work plus electricity, or 36 GJ/ha-yr of ethanol/car work. At best, this plantation will produce energy at a net loss of 28%; at worst the loss will be 76%.  The numbers are set down in the following table for easy comparison.
|Energy Production of an Acacia Plantation, Gross & Net|
|Energy Form||Gross in GJ/ha-yr||Net (-153 GJ/ha-yr)||Net Percentage|
|FT Diesel Fuel & Electricity||92||-61||-40%|
Biodiesel also contains 11% less energy per gallon than petroleum diesel. This results in reduced fuel economy. Even in a blend of 20% biodiesel, vehicles will travel 2.2 % (20% X 11%) fewer miles than with pure petroleum diesel. 
Yellow grease aficionados like to talk about how their vehicles do not pollute but only give off an odor of french fries. This is not entirely true. While biodiesel releases much less carbon dioxide than petroleum fuels, it is not emission free. Biodiesel has a higher oxygen content than petroleum fuels, about 11% by weight. This oxygen content improves the combustion and therefore lowers hydrocarbon, carbon monoxide, and particulate emissions. But the higher oxygen content does raise nitrogen oxide emissions appreciably. Oxides of nitrogen are ozone precursors.  So increased biodiesel use will result in more smog.
Biodiesel from Soybeans or Sunflowers
Pimentel and Patzek performed a thorough net energy analysis for deriving biodiesel from soybeans and sunflower seeds.  In comparing the two, they found that, while soybeans contain less oil than sunflower seeds (18% and 26% respectively), the yield of soybeans is almost twice as productive by weight (2,668 kilograms/hectare for soybeans, 1,500 kg/ha for sunflowers).  One hectare of soybeans will produce, on average, 480 kg of oil, while a hectare of sunflowers will produce only 390 kg of oil.
Soybeans also have the advantage of fixing their own nitrogen. This means that they can be grown without (or nearly without) nitrogen fertilizers, which is perhaps the largest single energy input in agriculture. Taking into account the differences in productivity and oil content, and the lower energy input for soybeans, to produce 1,000 kg of oil requires 5,556 kg of soybeans with an energy input of 7.8 million kcals, or 3,920 kg of sunflowers with an energy input of 156.0 million kcals. 
Processing into oil and refining into biodiesel is extremely energy intensive for both crops. The total energy input to produce 1,000 kg of soy oil, from the field to the factory is 11.9 million kcal, while the soy oil produced will have an energy content of 9 million kcal. So soy oil contains about 32% less energy than the energy taken to grow and process it. Pimentel and Patzek do give soy oil a substantial energy credit for the coproduct soy meal, which they give an energy value of 2.2 million kcal. This lowers the net energy loss to 8%. 
The results for sunflower oil are even worse. Production of 1,000 kg of sunflower oil requires a total energy input of 19.6 million kcal, while the sunflower oil produced will have an energy content of 9 million kcal. This results in a net energy loss of 118%.  In the case of sunflower oil, there is no energy credit from coproducts to offset this loss.
Using prices and dollar values from 2002, soy based biodiesel costs 84¢ per liter, or about $3.19 per gallon to produce. Thus soy oil is about 2.8 times as expensive as petroleum diesel to produce. Sunflower oil would cost $1.53 per liter, or $5.81 per gallon to produce. Sunflower oil is about 5.1 times as expensive as petroleum diesel to produce.  Of course, these prices are subject to change. Particularly, as the price of fossil fuels go up, so will the input costs and — accordingly — the net cost for producing soy oil and sunflower oil.
Biodiesel from Tropical Tree Plantations
Most of the biodiesel currently being produced on a commercial scale comes from tropical plantations of Acacia species (palm oil) and Eucalypts species. These monoculture plantations supplant biologically diverse rainforest. As global demand for biodiesel increases, so will the number and size of tropical plantations, particularly of Acacia species. The Intergovernmental Panel on Climate Change envisions 385 million hectares of biomass plantations by 2050. This is equivalent to one quarter of all currently planted agricultural land. Most of these plantations will replace tropical forest in developing countries. In order to achieve such a goal, biodiesel plantations would replace half of the tropical rainforests remaining on the planet. 
Tropical soils are extremely nutrient poor. Tropical forests derive most of their nutrients from organic matterâ€”decaying plants. The nutrient riches of tropical forests are found in the forest itself, and are stringently recycled. When tropical forest is cleared, particularly by slash and burn, what is left is a very poor soil that will become a completely infertile hardpack within a decade or so. In order to sustain any sort of agriculture, the soil must be pumped full of nutrients on an annual basis.
For a eucalypt plantation, the total restoration work is 49.1 GJ/ha-yr. While the input for eucalypts is much less than for acacias, eucalypt plantations are not nearly so productive as acacia plantations. So the eucalypt plantation can produce 27.3 GJ/ha-yr electricity, 22.9 GJ/ha-yr of FT diesel fuel/car work plus electricity, or 9.0 GJ/ha-yr of ethanol/car work. At best, this plantation will produce energy at a net loss of 44%; at worst the loss will be 81%.  See the following table.
|Energy Production of a Eucalypt Plantation, Gross & Net|
|Energy Form||Gross in GJ/ha-yr||Net (-49.1 GJ/ha-yr)||Net Percentage|
|FT Diesel Fuel & Electricity||22.9||-26.2||-53%|
This analysis plainly shows that neither acacia nor eucalypt plantations are sustainable from a net energy standpoint. The wood-to-energy industry might be feasible where wood pellets are generated as a byproduct of another industry such as paper milling or timber production. However, such an industry would be limited in size.
In his excellent article, Worse than Fossil Fuel, George Monbiot examines the destructive nature of palm oil plantations.  Palm oil plantations are responsible for more than 87% of the deforestation in Malaysia. As of now, virtually all of the remaining tropical forest is at risk of being cleared for palm oil plantations. Orang-utans, Sumatran rhinos, tigers, gibbons, tapirs, and proboscis monkeys are just some of the thousands of species faced with extinction in the wild. The fires of Malaysia, which rain out in China and Japan and pump many tons of carbon into the atmosphere annually, are set to clear tropical forest for palm oil plantations.
All of this for an industry that is not viable on a net energy basis. If palm oil & Eucalypt biodiesel plantations were oil fields, they would never have been tapped because of their net energy losses.
Ethanol from Sugarcane
Biofuel fanatics like to point at Brazils sugarcane/ethanol industry as a model for successful biofuel production. Many faulty and incomplete energy studies have made extravagant claims about the net energy generated in the Brazilian ethanol from sugarcane industry. One of the major problems with these studies is that they only look at the amount of ethanol produced. In order to complete the examination, all biofuels need to be assessed for the amount of shaft work they can perform. Once this is done, a very different picture emerges.
Sugarcane is a member of the grass family that can only be grown in warm climates where the temperature never falls below freezing. The growth period for this plant is 12 months. Thus it must be harvested on an annual basis. In 1000 kg of raw sugarcane, there are approximately 140 kg of bagasse,  160 kg of Brix,  92 kg of attached tops and leaves, and 608 kg of water. Sugarcane contains 70% moisture. Not included in this breakdown are 188 kg of detached, dead leaves. 
Brazil is the largest producer of sugarcane in the world, followed by India. In 2002, Brazil harvested an average 71.4 tonnes/ha-yr of sugarcane stems. With 5.2 million hectares in production, the 2002 Brazilian sugarcane harvest came to 372 million tonnes. On average, Brazil produced 4.4 tonnes of ethanol/ha-yr in 2002 (5525 liters/ha-yr or 1454 gallons/ha-yr). The gross energy value of this ethanol was 130.4 GJ/ha-yr. 
In Brazil, bagasse is used to generate all of the steam and electricity necessary to crush the cane, squeeze out the juice, ferment it, and distill it into 100% ethanol. Bagasse is also used to dry the bagasse and attached tops and leaves from 50% and 74% (respectively) moisture by weight, to 10% water content. The trash and bagasse produce a little extra electricity, 3.3 GJ/ha-yr. This brings the total energy production of sugarcane to 133.7 GJ/ha-yr. 
When 130.4 GJ/ha-yr of ethanol are used to fuel a 35% Carnot engine, the resulting shaft work is 45.6 GJ/ha-yr. Interestingly, it takes 130.2 GJ/ha-yr of energy to generate ethanol in the factory (not including the cost of water remediation).  Fortunately, all of this energy comes from the bagasse and trash.
The soils of Brazilian sugarcane plantations are typically nutrient poor tropical soils. And biomass production from sugarcane relies on processing the whole plant, stripping a maximum of nutrients from the plantation. Dead waste leaves are typically burned during the harvest. Instead, these waste leaves should be recycled into the soil, along with the filter cake generated in the ethanol factory. Brazilian sugarcane plantations are declining in productivity. Every effort should be made to recycle supposed wastes. Though the small plantations that produce most of the sugarcane grossly under-fertilize their soils, fertilizer is still a large expense in sugarcane production.
Another major expense is water remediation. Ethanol distilleries consume 25-175 liters of water per liter of ethanol produced. Water is used directly in yeast propagation, molasses preparation, and a host of other processes, and indirectly in steam generation, cooling, etc. Remediation of wastewater costs 18.6 GJ/ha-yr. 
There are additional pollution costs that have not been accounted for. Ethanol distilleries require large settling ponds that contaminate ground and surface water. This damage has gone largely untreated. And there is the problem of vinasse. This is a byproduct of sugarcane distillation that has a high BOD  and is very acidic. It is produced in quantities up to 15 times larger than the amount of ethanol. As of yet, there is no easy and economical means of disposing of vinasse. 
Adding together water remediation, diesel fuel to power plantation equipment, transportation fuel, fertilizer costs, the embodied energy in plantation and refinery machinery, the energy required to hybridize seed, and the energy of herbicides and insecticides, at minimum the energy costs of ethanol production average 63.6 GJ/ha-yr. This does not include the energy of ethanol distillation, which is assumed to come entirely from the bagasse and plant wastes. Thus, when burned in a 35% efficient Carnot engine, sugarcane ethanol has a negative net energy of -18 GJ/ha-yr. To put it another way, it takes 36% more energy to produce sugarcane ethanol than the amount of shaft work you can get out of the ethanol in a 35% efficient Carnot engine.
Sugarcane ethanol production in Brazil is successful only due to large government subsidies. As these subsidies dry up, it is hard to see how the industry could continue. Studies suggesting positive energy returns for sugarcane ethanol are fundamentally incomplete and therefore wrong.
Ethanol from Corn
Dr. Tad Patzeks Thermodynamics of the Corn-Ethanol Biofuel Cycle  is the most thorough examination of ethanol energy production to date. In this paper, Dr. Patzek performs both a traditional mass and energy balance according to the First Law of Thermodynamics, and a Second Law analysis based on exergy.  It is from this Second Law analysis that we can derive the answer to questions about the sustainability of corn-ethanol. The paper also reviews a number of other ethanol studies, correcting their inputs and calculations for comparisons sake.
The inputs to corn production are:
Fertilizer — particularly nitrogen fertilizer — is the largest energy input into corn farming (Patzek estimates about 54 KJ/kg of nitrogen). Fertilizer is followed, in order, by fuels, machinery, seeds, labor, herbicides and insecticides, transportation and electricity. The hybridization of corn seed is very expensive, requiring 107 MJ/kg, or about seven times the energy contained in the same mass of corn grain. The irrigation costs (15% of corn crops are irrigated) are figured into the fossil fuel expenses. In all, Patzek estimates that corn production requires about 28 GJ/ha. 
The average yearly yield of corn in the US from 2001 through 2003 was 8600 kg/ha of moist corn. Given that corn contains 15% moisture, this equates to 7300 kg/ha of dry corn.  Patzek points out that the amount of sunlight that irradiates a hectare of land during the growing season dwarfs all the energy inputs and the calorific content of the corn combined. Roughly only ~0.7% of incipient solar energy is converted by corn plants into biomass.  This means that solar energy does not limit corn production. The limiting factors for corn production (and for most agriculture) are soil, water and dissolved nutrients. Unfortunately, all of these are considered to be nonrenewable resources on a human time scale. We will discuss the implications later in this report.
The total energy required to generate ethanol from corn grain is about 15 MJ/L of ethanol. The largest energy inputs are the steam energy used to dry the corn, the electricity used in fermentation and distillation, transportation, and the energy used to build the ethanol plant and the machinery contained therein. Combining the energy costs for corn farming and ethanol refinement, Patzek estimates a total energy cost around 75 GJ/ha. He places the calorific content of ethanol at about 68 GJ/ha, for a net loss of 7 GJ/ha.  Therefore, ethanol production requires about 10% more energy than it provides according to a First Law Analysis.
Now we turn to the Second Law analysis. The Second Law of Thermodynamics  is all about entropy. Entropy is the measure of the amount of energy in a physical system that can be used to do work. The higher the entropy, the less energy that is available to do work. All physical systems move from a state of low entropy to a state of high entropy. The amount of energy available in a system is always less than the total energy of the system. Whenever energy changes forms, or is used, a portion of it is lost to entropy. A few examples will illustrate this point.
Crude oil has a very low entropy. A barrel of oil contains a vast amount of energy available to do work; this is why oil is so important to industrialization. When you burn oil in an internal combustion engine, you generate work, but you also generate a lot of heat that is dissipated to the environment. That heat loss is entropy. You may be able to reduce the amount of heat lost, but you will not be able to prevent it entirely.
When we mine a raw ore and refine it into a pure metal, it seems like we are creating low entropy from high. However, we must take into account the amount of entropy produced by the mining and smelting of the ore. In the end, we use a greater amount of low entropy (in the form of fossil fuels) than the difference between the entropy of the refined metal and the metal ore.
Soil is a low entropy substance. When plants grow on soil, they use up the low entropy of the soil as they extract nutrients from the soil. A natural ecosystem is considered sustainable because the plants bring in energy from sunlight to compensate for the entropy they create, and because the dead plants are recycled into the soil. In a natural ecosystem, entropy increases slower than the input of sun energy and the development of new soil from substrate.
All living things are entropy creating machines. All life is maintained by processing the energy available from low entropy systems, while depositing higher entropy elsewhere. In this regard, human beings are superior entropy producing machines. Humans extract nourishment and all other material products from low energy environments and transform it to high entropy end products, i.e. pollution.
In modern agriculture, we have boosted the production of cropland far beyond normal limits, and we have appropriated most of the product. Just as in the case of mining and refining ore, we do this through the use of fossil fuels. However, to practice modern agriculture, we must produce vast amounts of entropy in various forms, i.e. soil depletion, water pollution, air pollution, sewage and solid wastes.
In order to perform a Second Law analysis of ethanol, you have to identify and quantify all of this entropy in order to compare the net energy of ethanol production. One of the easiest ways to do this is through the derivation of exergy, which is the available free energy. When determining the exergy of pollution remediation, we must determine the amount of work necessary to return the polluted system back to a pristine state.
When a Second Law analysis of corn-ethanol is performed, we find that the minimum cumulative exergy consumption in restoring all the pollution and depletion of industrial corn-ethanol production is more than 7 times higher than the maximum amount of shaft work produced by a car engine burning ethanol. And this is excluding restoration work for decontaminating aquifers, rivers and the Gulf of Mexico, all tainted by agricultural runoff. Moreover, when you take into account all of the fossil fuel inputs, one hectare of corn-for-ethanol generates 7475 kg of CO2, or 2200 kg more CO2than would be generated by burning an energy equivalent amount of gasoline. In other words ethanol generation produces 42% more atmospheric CO2 than gasoline. 
Let me restate this for emphasis. The main reason why we are currently subsidizing ethanol production is the mistaken belief that ethanol contributes less CO2 than gasoline. There is also talk about ethanol being a renewable fuel source. However, in reality, ethanol produces 42% more atmospheric CO2 than an equivalent amount of gasoline, and it requires 10% more energy to produce than it provides. What is more, to remediate all the pollution of corn-ethanol production would require a minimum of 7 times the maximum amount of work that ethanol can produce in a car engine.
Industrial corn-ethanol production is not renewable and it is far from sustainable. Furthermore, analysis shows that there are no process changes that can make the system viable. We would be better off to abandon corn ethanol production right now.
Other Problems with Corn-Ethanol
Not only does ethanol not reduce the emission of greenhouse gases, ethanol burning contributes notable amounts of atmospheric nitrogen oxides, which then combine with volatile organic compounds (VOCs) to produce ozone. Studies show conclusively that ethanol leads to an increased ozone problem.  Within half a year of switching entirely to ethanol additives, California ozone levels rose 22%, and exceedences of the 8 hour standard rose to a maximum concentration of 40%. 
Ethanol plants are also notorious polluters, emitting ethanol vapors, carbon monoxide, VOCs, and carcinogens. In the last few years, the EPA has had to crack down on ethanol plants discharging 5 to 430 times more VOCs and carcinogens than their permits allow. The EPA has stated that the problem is common to most, if not all, ethanol plants. As of 2002, there were 61 ethanol plants in the US, located mostly in the Midwest, with another 14 under construction. 
Federal and state tax dollars currently subsidize ethanol production to the tune of about $3 billion per year. Without these subsidies, the industry would not be viable. Adding in subsidies for corn production brings this total up to $8.4 billion per year. Including the subsidies for ethanol plus the subsidies for corn production brings the price to $3/gallon (in 2003 dollars). Adding in all of the production costs would bring the price up to $4.71/gallon. Finally, considering that a gallon of gasoline contains 60% more energy than a gallon of ethanol, we can raise that price to $7.14 for an amount of energy equivalent to a gallon gasoline. For comparison, a gallon of gasoline costs $1.25 to refine (in 2003 dollars). 
Ethanol and corn subsidies also drive up the price of corn in general. About 70% of all corn grain produced in the US is fed to livestock. It has been estimated that ethanol production adds more than $1 billion to the price of beef production. So, as ethanol production expands, on top of the ethanol and corn subsidies, we can expect to pay higher prices for meat, eggs, and dairy products. 
It might be different if all of these subsidies were going to hard working farmers, but they arent. A conservative calculation suggests that individual corn farmers are receiving a maximum subsidy of 2¢ per bushel, or less than $2.80 per acre. Most of the profit is going to several large and profitable corporations, in particular Archer Daniels Midland. 
The US ethanol industry is highly concentrated among a few powerful corporations. According to the US General Accounting Office, Archer Daniels Midland controls 41% of the ethanol market. Adding in Minnesota Corn Processors (6%), Williams Bio-Energy (6%), and Cargill (5%), the top four producers control 58% of the market. Rounding out the list of top producers is High Plains Corp. (4%), New Energy Corp. (4%), Midwest Grain (4%), and Chief Ethanol (3%), for a total of 73% of ethanol production controlled by 8 corporations. 
From U.S. Ethanol Market: MTBE Ban in California. US General Accounting Office.
However, the situation is worse than the GOA report indicates, because the GOA does not consider marketing agreements. It is speculated that with market agreements, Archer Daniels Midland controls over half of the ethanol supply, while the top four companies together control 95% of the supply. 
One refiner holds the patents covering the use of ethanol in gasoline that meets Californias stringent standards. So far, the refiner has chosen not to enforce the patents.  But should the potential profits become large enough, what then?
Corn-ethanol solves nothing. If we continue to subsidize ethanol production, much less increase it, the result will be to further enrich a few powerful corporations while increasing the amount of global warming, ozone smog, water pollution, soil depletion, raising the price of gasoline at the pump, increasing our dependency upon fossil fuels and placing further unwarranted strain upon the pocketbooks of average consumers.
Ethanol from Switchgrass and Wood Cellulose
On average, a hectare of switchgrass requires an energy input of 3.8 million kcal per year. Given a maximum yield of 10 t/ha/yr, pelletized to burn in stoves, the return is about 14.6 kcal for each kcal invested. The cost of switchgrass pellets ranges from $94 to $130 per ton.  Thus, palletized switchgrass would be an excellent fuel for wood stoves.
Unfortunately, processing switchgrass into ethanol leads to a 50% energy loss. The cost of a gallon of ethanol produced from switchgrass is 20% higher than ethanol produced from corn. 
Converting wood cellulose to ethanol results in a 57% energy loss. The cost of a gallon of ethanol produced from wood cellulose would be 29% higher than ethanol produced from corn. 
Scientists are experimenting with genetically modified or bioengineered bacteria that will feed on cellulose and produce ethanol. To quote Cal Hodge, the president of A Opinion Inc (an advisory firm on regulatory, clean fuels, and economic issues), «Can we trust an industry that is emitting 5-430 times their permitted emissions levels to contain a new creation that has the potential to literally eat us out of house and home? Do the benefits justify the risk?» 
This is a little overstated. It is unlikely that escaped cellulose digesting organisms could eat us out of house and home. But they might be able to breed on decaying plant matter. So there is a possibility that they could seriously disrupt the nutrient cycle in a wide variety of habitats.
And they certainly are not green. This review has indicated that biofuels result in more atmospheric CO2 pollutants than burning an energy equivalent amount of oil. In the case of ethanol, dangerous amounts of nitrogen oxides are also emitted. And then there is the problem of agricultural runoff attributable to industrial biofuel farming. Increasing our usage of biofuels would lead to an increase in many types of pollution, along with soil and water depletion. Environmentalists would be wise to reject biofuels right now, before the damage is done.
The idea that we could replace our oil consumption with biofuels is really preposterous when you look at it closely. Fossil fuels are biofuels. And they are the only biofuels that will ever be plentiful enough to support our current energy consumption. An average gallon of gasoline required approximately 90 metric tons of plant matter as precursor material.  It took many thousands of years for this plant matter to accumulate, and then it took millions of years to process this plant matter into fossil fuels. In 1997, we burned fossil fuels containing the over 400 times the net primary productivity (NPP) of the Earths current biota — that is, all the plants and animals produced on this planet over the past 4 centuries. And our fossil fuel consumption has only increased since 1997.
Biologist Jeffrey Dukes estimates that to replace all of our fossil fuel consumption with biofuels would require, at the very least, 22% of terrestrial NPP. He adds the caveat that the requirement would be dramatically larger if biofuel production remains less energy efficient than the generation of energy from fossil fuels.  At present, 39% of the planets potential photosynthetic capabilities are appropriated by humans.  Dr. Dukes estimates that full scale biofuels production (using a more efficient technology than is currently available) would require another 19% of the planets photosynthetic resources.  With humans appropriating at least 58% of Earths photosynthetic potential, how would the biosphere survive on what was left?
The fact is that we have already appropriated all the prime productive agricultural land on the planet. Increasing biofuel production, particularly ethanol from corn, will have to compete with food crops. Will we push more marginal and impoverished peoples into malnourishment and starvation simply so that the rich can have fuel for their vehicles, and corporations such as Archers Daniels Midland can boast higher profits?
Sustainable systems are cyclical. This is what makes them sustainable. They do not lose a significant amount of nutrients. And the energy lost to entropy must be more than compensated by incoming solar energy. Industrial systems are linear. They take a resource, and process it into a product which is eventually discarded once it has outlived its usefulness. All well-meaning attempts at recycling notwithstanding, industrial systems are not sustainable.
Modern agriculture is an industrial system, and as such, it is not sustainable. Nutrients extracted from the soil are removed from the farmland in the form of vegetable matter, and shipped to consumers. After being eaten, the nutrients are excreted as human wastes and then disposed of as sewage. Industrial agriculture breaks the cycle, leading on the one hand to soil and water depletion and on the other to pollution problems with raw sewage. Modern agriculture is a form of soil mining. And many of the worlds most productive soil mines would have played out already, but for the application of fossil fuel based fertilizers. Bioengineer Fölke Gunther has explored the possibility of reconnecting the food cycle,61 but his study is beyond the focus of this paper.
In food farming, the plant matter that is not harvested could (and should) be returned to the soil in an effort to help limit soil nutrient depletion, and to help limit erosion. Industrial production of biofuels depends on utilizing everything that can be harvested from the plantation or field. The nutrients removed from the ground in the form of biomass must be replaced with artificial fertilizers. And even then, soil depletion is hastened and the productivity of the crop land diminishes significantly from one generation to the next until it must be abandoned as unproductive. As it is, industrial agriculture has brought us to the brink of an agricultural crisis. 
For this reason alone, biofuel production can never be sustainable. And, therefore, biofuels are not renewable.
Biofuels are not even an efficient way of harnessing solar energy, as exemplified in the following graphs. The first graph compares the total solar energy available per hectare of cropland for a period of 120 days (a growing season for corn) with the combined fossil fuel inputs and corn energy content figures derived from four different studies. The second graph compares the average incoming solar power in the tropics with the amount of energy contained in oil (burned in a 35% efficient Carnot engine), a horizontal solar cell, sugarcane, corn, acacia, and eucalypt plantations.
From, Thermodynamics of the Corn-Ethanol Fuel Cycle, Patzek,
Critical Reviews in Plant Sciences, 23(6):519-567, 2004.
From Thermodynamics of Energy Production from Biomass, Patzek,
Tad W. & Pimentel, David.
Critical Reviews in Plant Sciences, March 14, 2005.
Our energy needs would be much better served if we would practice energy conservation, strive for better energy efficiency, and divert current biofuel subsidies to the development of affordable and more efficient solar cells and wind turbines.
Dale Allen Pfeiffer,