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Feedstocks and energy crops
Bioenergy uses biomass -- plant matter or animal waste -- to produce electricity, fuels and heat. Examples include ethanol motor fuel, landfill gas and wood burned in fireplaces and stoves. EMS's biomass web pages deal mainly with ethanol motor fuel and the use of plant matter to generate electricity in power plants.
Current ethanol production uses the kernels from the corn plant. Farming of corn is a relatively energy-intensive process, but ethanol from corn still yields 34 percent more energy than the total amount required to farm the corn and make the ethanol.
(Source: U.S. Department of Agriculture - PDF)
Other crops have a much higher energy yield: Ethanol made from "energy crops" -- grasses and trees -- yields 4-5 times as much energy as needed to farm the crops and make the ethanol.
The Department of Energy (DOE) believes that we could produce 10 percent of our transportation fuels from biomass by 2010, and as much as 50 percent by 2030. For electricity, DOE estimates that biomass could supply 5 percent by 2010, while the Electric Power Research Institute puts the portion at 8 percent.
"Repowering the Midwest," a report by environmental groups, estimates that energy crops and waste biomass from the Midwest alone could provide about 16 percent of the country's electricity, without irrigation and without competing with food crops.
The extensive subsidy programs for both food crops and fossil fuels have created a substantial barrier to energy crops, according to the Union of Concerned Scientists.
Use of biomass as a fuel offers some environmental advantages over fossil fuels like coal and oil, but can also have significant negative impacts on the environment. Some environmental groups support development of biomass energy depending on factors such as:
Choice of biomass "feedstock" used to make the fuel (e.g. crop wastes, trees and grasses, corn, etc.)
The manner in which crops are farmed (whether there is heavy use of pesticides and fertilizers, use of irrigation, etc.)
The effectiveness of pollution controls used when energy is generated.
Most environmental groups do not promote ethanol as a strategy for reducing smog. In particular, the Sierra Club and Clean Air Trust have voiced concerns that ethanol may actually lead to an increase in smog-forming pollutants. Indeed, studies show that adding a small amount of ethanol to gasoline can lead to a slight increase in formation of smog. On the other hand, motor fuels comprised primarily of ethanol (mixtures containing upwards of 80 percent ethanol) are thought to reduce smog, compared with conventional gasoline. Find out more.
Some environmental groups support use of biomass energy as a way to reduce America's fossil fuel dependence and to help combat global warming. Energy crops can play a significant role in addressing global warming and fossil fuel dependence; ethanol made from corn provides, at best, only a small benefit because of the amount of petroleum required to farm corn.
Power plants or automobile engines that generate energy from biomass can emit no more carbon than the biomass crops have absorbed from the atmosphere, so there are no net carbon emissions from the fuel itself. However, a significant amount of energy is needed to farm the crops -- particularly in the case of food crops, such as corn, that require annual plowing and replanting and typically are grown with fertilizers and pesticides. To the extent that the energy used to farm biomass crops is generated by burning fossil fuels, biomass energy has a global warming impact. Farming of biomass crops can also have the affect of releasing soil carbon into the atmosphere.
American Lands Alliance has expressed concerns that native forests will be replaced with "tree farms" to grow fuel for bioenergy generation.
While formation of smog (ground-level ozone) is a complex process involving many factors, studies indicate that motor fuel comprised of at least 80 percent ethanol can reduce smog, while a gasoline/ethanol mixture containing less than 80 percent ethanol appears to lead to a small increase in smog.But the debate over the use of ethanol as a more enviromentally friendly alternative fuel will no doubt continue.
Blending of small amounts of ethanol into gasoline has little impact, or a small net positive impact, on smog formation:
According to a May 1999 report by a committee of the National Academies of Sciences (NAS), addition of oxygenates such as MTBE and ethanol to gasoline "has little impact on improving ozone air quality." The NAS press release says "the overall impact of either oxygen additive [ethanol or MTBE] on reducing ozone -- a major component of smog -- is very small."
In July 2001, the Northeast States for Coordinated Air Use Management issued a report, "Health, Environmental, and Economic Impacts of Adding Ethanol to Gasoline in the Northeast States." According to the report, "ethanol-blends provide ... lower rates of carbon monoxide and particulate emissions, as well as greenhouse gas benefits." The report suggests that blending of ethanol into gasoline increases some of the chemical emissions that contribute to smog, such as NOx and VOCs, while reducing emissions of carbon monoxide, another factor in the formation of smog: "With ethanol, the carbon monoxide benefits will partially offset the adverse ozone impacts associated with increased NOx and VOC emissions."
An ethanol/gasoline mix containing upwards of 80 percent ethanol appears to reduce formation of smog:
According to the website of the American Lung Association, "ethanol produces lower emissions of ozone-forming compounds and toxic air pollutants" than gasoline, when 85 percent ethanol is blended with 15 percent gasoline.
A study by Jennifer L. Brand, a researcher at the University of Nebraska-Lincoln, found that a gasoline mixture with 10 percent ethanol leads to increased evaporative, smog-forming emissions, compared with standard gasoline. Brand concluded that smog-forming emissions are reduced only when the ethanol portion of the fuel mixture approaches 80 percent, according to a June 2001 article in the Grand Island Independent (Nebraska).
The Renewable Fuels Association, a trade group, says on its website that ethanol reduces smog: "Some ethanol opponents seize upon the fact that when ethanol is blended with gasoline, it slightly raises the volatility of the fuel. Increased volatility can lead to increased evaporation of smog-forming emissions. But as is often the case, this is only half the story. Blending ethanol in gasoline dramatically reduces carbon monoxide tailpipe emissions. According to the National Research Council, carbon monoxide emissions are responsible for as much as 20 percent of smog formation. Additionally, ethanol-blended fuels reduce tailpipe emissions of volatile organic compounds, which readily form ozone in the atmosphere. Thus, the use of ethanol plays an important role in smog reduction."
A very recent report done in 2009 concluded, that with "Recent improvements in crop production,biorefinery operation, and coproduct utilization in U.S. corn-ethanol systems result in greater GHG emissions reduction, energy efficiency, and ethanol-to-petroleum output/input ratios compared to previous studies. Direct-effect GHG emissions reductions were found to be 48% to 59% compared to gasoline, which is two to three times greater than estimated in previous reports (Farrell et al. 2006). The NER has improved from 1.2 in previous studies to 1.5 to 1.8 on the basis of updated data. Ethanol-to-petroleum ratios were 10:1 to 13:1 for today’s typical corn-ethanol systems but could increase to 19:1 with progressive crop management that increases both yield and input use efficiency. A closed-loop biorefinery with an AD system reduces GHG emission by 67% and increases the net energy ratio to 2.2. Such improved performance moves corn-ethanol much closer to the hypothetical estimates for cellulosic biofuels.
The critics of this study say that it does not take into consideration the effects of the changes to land use by concentrating more acreage to growing corn at the expense of other vital crops such as soy beans.This will increase the presure on remaing land to be cleared for even more crop growing and thus affect the enviroment negatively in that way