Ethanol fuel energy balance

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Ethanol is one of many proposed replacements for petroleum-derived liquid fuels for transportation purposes. As a liquid fuel, like gasoline and diesel, it has a high energy density, it is easily and safely handled, transported, and distributed, without the need for expensive, heavy, and fragile cryogenic and/or high pressure systems which are needed for gaseous fuels.

Ethanol is touted as a renewable fuel. This statement can be justified if ethanol is produced by fermenting biomass instead of the more common hydration of ethylene derived from petroleum feedstock. It is also CO₂-neutral in that no "new" carbon is released; by fermenting biomass, there is no net increase in carbon dioxide which does occur when fossil fuels are burned. This is a contentious statement, though, because at present, the production of ethanol, even from biomass, does require inputs of fossil fuel, as is discussed subsequently.

[edit] Variables

For ethanol to contribute significantly to transportation fuel needs, it would need to have a positive net energy balance and according to DoE it has. ^{[1] [2]} To evaluate the net energy of ethanol four variables must be considered:

1. the amount of energy contained in the final ethanol product
2. the amount of energy directly consumed to make the ethanol (such as the diesel used in tractors)
3. the quality of the resulting ethanol compared to the quality of refined gasoline
4. the energy indirectly consumed (in order to make the ethanol processing plant, etc).

Although a topic of debate, some research that ignores energy quality suggests it takes as much or more fossil fuel energy (in the forms of diesel, natural gas and coal) to create an equivalent amount of energy in the form of ethanol^[3]. In other words, the energy needed to run the tractors, produce the fertilizer, process the ethanol, and the energy associated with the wear and tear on all of the equipment used in the process (known as fixed asset depreciation to economists) may be more than the energy derived from burning ethanol.

Two important flaws are cited in response to that argument:

1. the energy quality is ignored, the economic effects of which may be significant. Principal economic effects of energy quality comparison are the cleanup costs of soil contamination stemming from gasoline releases to the environment and medical costs from air pollution resulting from refining and burning gasoline. Ethanol's higher octane rating may also allow for more thermally efficient conversion of chemical energy into mechanical energy.
2. the inclusion of development of ethanol plants instills a bias against the product based strictly upon the pre-existence of gasoline refining capacity. The real decision should be based upon the long-term economic and social returns.

The first counter-argument, however, is contested. Burning a gallon of cleaner ethanol is still pointless if it implicitly requires burning two gallons of dirty gasoline to create that ethanol in the first place. New techniques for producing ethanol from plant cellulose (cellulosic ethanol) create more ethanol per unit of energy input, and may fundamentally shift production to a positive energy balance when they reach economies of scale. Cellulosic ethanol can also be created from farm residue such as wheat straw, further defraying the energy costs of production.

[edit] System Borders

Much of the current academic discussion regarding ethanol currently revolves around issues of system borders. This refers to how complete of a picture is drawn for energy inputs. There is debate on whether to include items like the energy required to feed the people tending and processing the corn, to erect and repair farm fences, even the amount of energy a tractor represents.

In addition, there is no consensus on what sort of value to give the rest of the corn (such as the stalk), commonly known as the 'coproduct.' Some studies leave it on the field to protect the soil from erosion and to add organic matter, while others take and burn the coproduct to power the ethanol plant, but do not address the resulting soil erosion (which would require energy in the form of fertilizer to replace). Depending on the ethanol study you read, net energy returns vary from .7-1.5 units of ethanol per unit of fossil fuel energy consumed. For comparison, that same one unit of fossil fuel invested in oil and gas extraction (in the lower 48 States) will yield 15 units of gasoline, a yield an order of magnitude better than current ethanol production technologies, ignoring the energy quality arguments above and the fact that the gain (14 units) is not carbon neutral. ^[4]

[edit] Extraction vs Production

Extraction is not the same as production. Each gallon of extracted oil is a gallon of depleted oil. To fairly compare the energy balance of gas production to ethanol production, one must also calculate the energy required to produce oil from the atmosphere and feed it back into the earth, a process that would make gasoline production fractionally efficient compared to ethanol.

[edit] Negative fuel energy balance

Switching to a system with negative fuel energy balance could increase the consumption of non-alcohol fuels. Such a system may only be worth considering as a way of exploiting and converting non-liquid fuels through the production of ethanol for transportation use, such as coal, natural gas, or biofuel from crop residues. (Indeed, many U.S. proposals assume the use of natural gas for distillation and fertilizer production.) However, many of the expected environmental and sustainability advantages of alcohol fuels may not be realized in a system with negative fuel balance. Before conclusions are drawn on the energy fuel balance calculations it would be necessary to factor in the annual medical costs associated with air pollution from gasoline and soil remediation costs of the gasoline alternative; combined the annual costs of these penalties to gasoline are on the order of one to ten billion dollars per annum in the U.S. and potentially treble that value worldwide.

Even a positive but small energy balance would be problematic: if the net fuel energy balance is 50%, then, in order to eliminate the use of non-alcohol fuels, it would be necessary to produce two units of alcohol for each unit of alcohol delivered to the consumer.

[edit] Geography

In this regard, geography is the decisive factor. In tropical regions with abundant water and land resources, such as Brazil and Colombia, the viability of production of ethanol from sugarcane is no longer in question; in fact, the burning of sugarcane residues (bagasse) generates far more energy than needed to operate the ethanol plants, and many of them are now selling electric energy to the utilities. However, while there may be a positive net energy return at the moment, recent research suggests that the sugercane plantations are not sustainable in the long run, as they are depleting the soil of nutrients and carbon matter (Reijnders 2004).

The picture is different for other regions, such as most of the United States, where the climate is too cool for sugarcane. In the U.S., agricultural ethanol is generally obtained from grain, chiefly corn.

[edit] References

1. ^ Popular Mechanics - Crunching The Numbers On Alternative Fuels Quote: "...according to the DOE, the growing, fermenting and distillation chain actually results in a surplus of energy that ranges from 34 to 66 percent..."
2. ^ DoE: Biomass Program: Net Energy Balance for Bioethanol Production and Use Quote: "...The most official study of the issue, which also reviews other studies, concludes that the "net energy balance" of making fuel ethanol from corn grain is 1.34...For cellulosic bioethanol—the focus of the Biomass Program—that study projects an energy balance of 2.62...A Biomass Program life-cycle analysis of producing ethanol from stover, now underway, is expected to show a very impressive net energy ratio of more than 5..."
3. ^ David Pimentel and Tad Patzek, "Ethanol Production Using Corn, Switchgrass and Wood", Natural Resources Research (March 2005), pp 65-76
4. ^ (pdf)

[edit] See also

• ethanol fuel
• energy balance