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Costs and Benefit of Ethanol and Biosiesel
Proceedings of the National Academy of Science
"Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels," by Jason Hill, et al., July, 12, 2006,
This is by far the best study to date, so zFacts is providing a pargraph-by-paragraph synopsis that's much easier to read. Get the PDF containing synopsis and supporting tables. For professional use or to quote, buy a copy for $10 from NAS. [Bracketed items are clarifications by zFacts.]
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Abstract. Environmental concerns and shortages of fossil fuels have spurred interest in biofuels for transportation. Biofuels should provide a net energy gain, environmental benefit, a competitive cost, and not reduce food supplies if widely used. This paper evaluates corn ethanol and soybean biodiesel on this basis. Ethanol yields 25% more energy and biodiesel 93% more than used to produce them. Biodiesel releases 100 times less agricultural nitrogen, and about 10 times less phosphorous and pesticides than ethanol. Ethanol use reduces greenhouse emissions by 12% and biodiesel by 41%. Neither biofuel can replace much petroleum without impacting food supplies. Even dedicating all U.S. corn and soybean production to biofuels would meet only 12% of gasoline demand and 6% of diesel demand. [While increasing other energy use.] Biodiesel provides sufficient environmental advantages to merit subsidy.
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Concerns over energy shortages and global warming have stimulated interest in transportation biofuels. Both direct and indirect inputs must be tracked in full to determine if these are beneficial. This paper determiners the net societal benefits of corn ethanol and biodiesel relative to gasoline and diesel by using current farm and fuel production data.
A desirable alternative fuel should be “economically competitive with” [by which the authors mean “almost as cheap as”] the fossil fuel it replaces, be environmentally superior, and be available in large quantities. It should also provide a net energy gain. Both fuels are analyzed as if produced by an “island economy” and considered to have a net energy gain only if the energy value of the island’s exports of fuel and coproducts exceeds the sum of direct and indirect energy inputs. (See Tables 1–6).
This paper estimates farm energy inputs for corn and soybeans, including energy to grow seed, power and produce farm machinery and buildings, produce fertilizers and pesticides, and sustain farmers and their households. Similar inputs are considered for biofuel production. Production outputs include the fuels and their coproducts. The fuels are assigned the energy available from the combustion [lower heating value]. Coproducts, such as DDGS and glycerol, are assigned their energy equivalent values.
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Results
Net Energy Balance (NEB). In spite of tracking indirect energy inputs so extensively, the paper shows that both corn ethanol and biodiesel have a positive NEB (see Fig. 1 and Tables 7 & 8). Energy out exceeds energy in. This reinforces recent finding (1–5). Although these earlier reports omit some indirect energy inputs, recent increases in crop yields and efficiencies offset the more complete inclusion of inputs found in this paper. These results counter the assertion that “expanding system boundaries” [including more indirect inputs] automatically causes negative NEB values (6–8). [Standard economic input-output analysis, developed in the 1930's, confirms this.] This paper finds no evidence that either biofuel requires more energy to make than it contains, but corn ethanol provides only 25% more energy than needed to produce it. The advantage of soybean biodiesel, which provides 93% excess energy remains no mater which of five different coproduct accounting methods is used (see Table 9). [At least four of these methods are incorrect, but checking them should help convince skeptics.] [The original Figure 1 contains far more detail than this simplification.]
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Life-Cycle Environmental Effects. Corn and soybean farming both degrade the environment by contaminating other habitats and water supplies with chemicals, especially nitrogen, phosphorus, and pesticides. Contamination of water by nitrogen and phosphorus causes over-enrichment and excessive plant growth, loss of biodiversity, and increased nitrate and nitrite in drinking water. Accounting for coproducts, per unit energy gained, biodiesel uses only 1.0% of the Nitrogen used by ethanol. Similarly, biodiesel uses 8.3% of the Phosphorus and 13% of the pesticides used by ethanol (Fig. 2ab; see also Table 10). These differences have substantial consequences, including nitrogen fertilizer for corn being a major contributor to the “dead” zone in the Gulf of Mexico (11) and to nitrate, nitrite, and pesticide residues in well water. Corn pesticides tend to be more harmful and long-lived than those used on soybeans (Fig 2b and Table).
“E10" (10% ethanol and 90% gasoline) can lower emission of carbon monoxide (CO), volatile organic [bad organic] compounds (VOC) and very small particulate matter (PM10). However, with “E85," total-life-cycle emissions of five major air pollutants are higher per unit energy than with gasoline (12). These are CO, VOC, PM10, sulfur oxides (SOx) and nitrogen oxides (NOx). Low levels of biodiesel blended into diesel reduce VOC, CO, PM10, and SOx during combustion, and biodiesel blends show reduced life-cycle emissions for CO, PM10, and SOx relative to diesel (5).
If CO2 from fossil fuel combustion was the only GHG (greenhouse gas) considered, a biofuel with NEB > 1 should reduce GHG emissions. [This is likely because the solar energy (plant) input is CO2 neutral, but the use of coal as an input tends to counteract this.] However nitrogen fertilizer and microbes can work together to release N20, a potent GHG (13). Analyses reported in Table 11 suggests that the use of corn ethanol releases 88% as much GHG as the equivalent use of gasoline (Fig. 2c). Another recent study found 87% using different methods (1). In contrast, biodiesel use releases 59% as much as equivalent diesel use. It is important to note that these estimates assume crops are harvested from land already in production; starting with intact ecosystems would result in reduced GHG savings or even reverse it.
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Economic Competitiveness and Net Social Benefits.
Because the environmental costs of fossil fuels are not capture in market prices, biofuels that impose fewer non-market costs deserve a subsidy to level the playing field. [Or we could tax fossil, or better yet, tax fossil fuel just enough to pay the biofuel subsidies.]
At average 2005 gasoline prices, it cost $1.74 to produce ethanol (14–16) compared with $1.67 for gasoline (17), while biodiesel (14–16) cost $2.08 compared with $1.74 for diesel (17). All of these values are wholesale prices per gasoline-gallon equivalent (GGE) of energy content. Although not cost competitive, the may have been profitable because of large subsidies. The federal government provides subsidies of $0.76 per GGE for ethanol [$0.51/gallon] and $1.10 per GGE for biodiesel (19). Demand for ethanol is also enhanced by laws and regulations which require blending some ethanol with gasoline [in some locations]. [This has recently raised wholesale prices above the level determined by the subsidy.] Ethanol and biodiesel producers also benefit from federal crop subsidies that lower corn prices (which are approximately half of ethanol production’s operating costs) and soybean prices.
Potential U.S. Supply. In 2005, 14.3% of the U.S. corn harvest was processed to produce 3.91 billion gallons of ethanol (20, 21), containing the same energy as 1.72% of U.S. gasoline usage (22). Similarly, 1.5% of the soybean harvest produced 67.6 million gallons of biodiesel (20, 23), which was 0.09% of U.S. diesel usage (22). Using the entire corn and soybean crops would have replaced 12% and 6% of gasoline and diesel usage. Because of their large fossil energy input requirements, this would have provided net energy gains of only 2.4% and 2.9% respectively. Using the all corn and soybeans for biofuels is unlikely because they are major food sources (e.g., high-fructose corn syrup and soybean oil), and sources of livestock feed.
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Discussion
Soybean biodiesel has major advantages over corn ethanol. It provides 93% more energy than its production consumes in fossil fuel, reduces several major air pollutants and reduces GHGs by 41%. It has minimal impact on human and environmental health through Nitrogen, Phosphorus, and pesticide release. By contrast corn ethanol provides only a 25% energy gain and a 12% reduction in GHGs and has greater environmental and human health impacts.
Biofuels would provide greater benefits if their agricultural inputs required less fertilizer, pesticide, and energy, and were produced on low-value land and required less energy to convert these inputs to biofuel. Neither corn ethanol nor soybean biodiesel do well on the first two criteria. Soybean biodiesel, however, requires far less conversion energy than corn ethanol (Fig. 1) because soybeans create long-chain triglycerides that are easily extracted. Corn starches must be converted to sugars with enzymes, the sugar fermented to alcohol by yeast, and the alcohol distilled to remove the water.
The NEB of both biofuels could be improved, and perhaps their costs reduced, by use of low-input crops or agricultural residues (such as corn stover) in place of fossil fuel in the conversion process. Switchgrass, diverse mixtures of prairie grasses and forbs (24, 25), and woody plants, can all be converted into synfuel hydrocarbons or cellulosic ethanol. These can be produced on marginal lands with no, or low, fertilizer, pesticides, and energy inputs (24, 25). For cellulosic ethanol, combustion of waste biomass, could power processing plants. Although gains may be reduced by increased energy for transport, construction of larger plants, and perhaps greater labor needs, resultant NEB ratios as high as 4.0 might still be possible (26, 27)—a major improvement on corn ethanol’s ratio of 1.25 and even biodiesel’s 1.93. Combined-cycle synfuel and electric cogeneration (30) may do as well or better than cellulosic ethanol. In sum, low-input biofuels save much more energy and have much lower environmental impacts per unit of fuel energy than do food-based biofuels.
Global demand for food is expected to double within the coming 50 years (31), and more than double for transportation energy (32). Food-based biofuels, which tend to be more damaging to the environment, can play only a small roll in meeting these needs, while energy conservation and non-food biofuels show far greater long-term promise (33).
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Methods
Energy Use in Crop Production. This study uses 2002–2004 USDA data on fertilizer, soil treatment, and pesticide usage for corn (Table 1) and soybeans (Table 2). Estimates of the energy needed to produce each of these inputs are derived from recent studies (2–7). The study also estimates energy use for operating equipment, manufacturing this equipment, constructing buildings used in crop production (Table 3), and for producing the hybrid (corn) or varietal (soybeans) seed planted. We transform these per-acre estimates into per-gallon estimates based on 388 gallons of ethanol per acre and 58 gallons of biodiesel per acre. The study also estimates the per-gallon-of-biofuel energy use to sustain farm households (Table 4).
Energy Use in Converting Crops to Biofuels. This study estimates the energy used to build conversion plants (Table 6), to transport crops and biofuels (Table 5), and to power the plants. Again, energy use by households of laborers is included (Table 4).
Energy Yield from Biofuel Production. This paper defines NEB and the NEB ratio as follows:
NEB = (energy in biofuel + energy credit of coproducts) – (total energy inputs)
NEB ratio = (energy in biofuel + energy credit of coproducts) / (total energy inputs)
For coproducts DDGS and glycerol, energy credit is assigned by the “economic displacement” method which assigns them the energy required to produce the marketplace products which are their closest substitutes. [This is the correct method because it answers the question, how much more energy would be used if we did not produce the biofuel? The choice of method for evaluating coproduct energy is not a matter of convention as many have asserted. For the question under examination, this is the only correct method. —zFacts] Specifically corn and soybean meal are evaluated to find the energy credit fo DDGS, and synthetic glycerol is evaluated for soybean-derived glycerol.
Soybean meal does not have an adequate substitute in the marketplace based on both its availability and protein quality, so this paper uses a “mass allocation” method to estimate its coproduct energy credit. This assigns the coproduct a credit equal to the total energy input to the production process times the ratio of coproduct weight to the weight of soybeans processed. [This method is incorrect, but it provides a rough guess of the correct energy credit. —zFacts] The paper also applies alternative methods of calculating coproduct credits including issuing energy values based on caloric content and market value (Table 9). [All of these methods are also incorrect, but they may give some idea of the inaccuracies caused by using incorrect methods. It would probably have been better make an estimate of what the market would have done in the absence of soybean meal. —zFacts]
Environmental Effects. Life-cycle environmental impacts include combustion and production, and are computed per unit of energy gained as measured by NEB. If the impact is X per gallon of biofuel, and the NEB is 0.24 GGE per gallon, then the impact is calculated as 0.24×X per gallon. This is done for fertilizer and pesticide application rates (Table 10) and for GHG savings. GHG savings includes savings from replacing the fossil fuel with the biofuel and emissions from producing the biofuel and from GHG released on the farm.
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zFacts footnotes.
1. Input-output analysis traces inputs back forever. This has been shown to give the correct answer, and input-output analysis provides the mathematics for doing these infinite sums. Suppose A requires 0.5 energy units plus half a unit of A. Then the total energy is 0.5 + 0.25 +0.125 + ... forever. This infinite sequence simply sums to 1, which is the correct total energy use.
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http://zfacts.com/p/349.html | 01/18/12 07:17 GMT
Modified: Wed, 26 Aug 2009 18:13:57 GMT
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