AgDM newsletter article, July 2007

Energy agriculture - ethanol energy balance

Don HofstrandDon Hofstrand, retired extension value added agriculture specialist, agdm@iastate.edu

Does it take more energy to make ethanol than is contained in the ethanol? This question has been debated for decades as an indicator of the value (or lack of value) of ethanol.

The answer is an emphatic “yes”. As shown in Table 1, it takes about 1.75 British thermal units (Btu) to make one Btu of corn ethanol at the fuel pump. The answer has to be yes because you would have “created” energy and broken one of the basic laws of physics if you ended up with more energy than you started with.

Table 1. Btu Used to Make One Btu at the Fuel Pump

A more relevant question is “What type of energy?” is used in the production of ethanol. For example, a large share of the energy for ethanol production (either corn or cellulosic) comes from sunlight, which is free to use and causes no environmental degradation.

If the analysis is restricted to just the fossil fuel energy used in producing ethanol (e.g. petroleum, natural gas, coal, etc.), it takes about .74 of a Btu to make one Btu of corn ethanol at the fuel pump. From a different perspective, one Btu of fossil fuels generates 1.36 Btu of ethanol (Table 2).

Table 2. British Thermal Units Generated from One Btu of Fossil Fuels

If we look just at the petroleum portion of the fossil fuels used in making ethanol, ethanol is a clear winner. Corn and cellulosic ethanol require about one-tenth of a Btu of petroleum to make a Btu of ethanol while gasoline requires more than one Btu of petroleum.

There is considerable controversy over the energy balance question. Although most research shows the energy balance to be in the neighborhood of the numbers discussed above, some researchers claim that it takes more fossil fuel energy to create ethanol than is contained in the ethanol. Others report that 1.77 Btu of ethanol are produced per Btu of fossil fuel in dry mill plants.

An argument can be made that ethanol is being held to a higher standard than other energy sources. For example, it takes about 1.23 Btu of fossil fuels to create one Btu of gasoline. To produce gasoline, crude oil needs to be recovered, transported and refined. Most of this is done with fossil fuels.

If ethanol is compared to other energy sources, it compares quite favorably. Conversely, electricity is one of the worst as shown in Table 2. Most electricity is generated in coal-fired plants, but there is little said about the poor energy balance because electricity is a more convenient energy source than coal. For example, it is easier to run your refrigerator on electricity than on coal. The electricity energy balance will improve and electricity will become a cleaner energy source as the portion of electricity produced from wind and solar power increases.

Trends in Energy Balance

To get a realistic view of the energy conversion picture, we must also examine where we have been in the past, and where we may go in the future. Approximately one-third of the fossil fuel energy required to produce a gallon of ethanol relates directly to corn production. The other two-thirds are due to converting the corn to ethanol.

As shown in Table 3, the conversion of corn to ethanol has improved substantially in recent years. This means that the fossil fuel used in corn production is spread over more gallons of ethanol. In addition, corn production has become more energy efficient. Corn output per pound of fertilizer has risen 70 percent in the last 35 years.

Table 3. Improvements in Conversion of Corn to Ethanol

In the 1980s, ethanol plants used 2.5 to 4.0 kWh of electricity per gallon of ethanol. Today it is significantly below 1 kWh. If the electricity is generated using wind or solar power, the consumption of fossil fuels is reduced even more. Overall, ethanol production today requires about 50 percent less energy than in the early 1980s. Currently, non-fossil fuel energy sources are being investigated as a substitute for natural gas.

A 1995 study (Table 4) outlined the industry average production using average practices in existence in terms of Btus of ethanol produced from a Btu of fossil fuels. It shows that the energy balance is significantly better (2.09) if we just consider the most efficient corn and ethanol producers. The state-of-the-art balance (2.51) is achievable by farmers and ethanol producers using all of the best and most energy efficient technologies and practices.

Table 4. Corn Ethanol Net Energy Balance

It seems reasonable that through improvements in management and technology the industry average will move toward the efficiencies of the “industry best” and even the “state-of-the-art”, and the new “industry best” and “state-of-the-art” will be at even higher levels.

Greenhouse Gas Emissions

Recent scientific research has confirmed the threat of global warming due to greenhouse gas emissions. So, reducing greenhouse gas emissions is an important energy goal. As shown in Table 5, corn ethanol blends have lower greenhouse gas emissions than straight gasoline. And cellulosic ethanol is about three times better than corn ethanol.

Table 5. Greenhouse Gas Emissions Reduction from Straight Gasoline

This reduction is true even though about one-third of the production (by weight) from a corn ethanol dry mill plant is carbon dioxide. And the carbon dioxide is usually vented into the air.

However, the carbon dioxide is part of the natural carbon cycle that does not create new carbon dioxide in the atmosphere. Plants, including corn, take in carbon dioxide for photosynthesis when they grow. When the plant dies and decomposes, the carbon dioxide is released back into the atmosphere. Instead of releasing the carbon dioxide when the corn kernels decompose, it is released when the corn kernels are processed.

By contrast, emissions from the use of fossil fuels pump new carbon dioxide into the atmosphere. These emissions are from carbon that was sequestered deep in the ground in the form of crude oil, coal, natural gas, etc.

Ethanol’s Lower Energy Content

Ethanol has been criticized because there are fewer Btu in a gallon of ethanol than a gallon of gasoline. As shown in Table 6, ethanol has only two-thirds percent the Btu of gasoline.

Table 6. Energy Content of Various Fuels

However, ethanol’s combustion efficiency makes up for some of its lower energy content. Due to ethanol’s octane rating of 113-115 as compared to 87 for unleaded gasoline, high-compression engines can perform just as well on fewer Btu.

There is probably significant variation in the ethanol mileage reduction among different brands and models of cars and light trucks. For example, the 2005 Flexible Fuel Ford Taurus has a 15 percent reduction in mileage (Popular Mechanics) when operated on E85 as compared to straight gasoline. From a personal level, checking your fuel mileage with both straight gasoline and E85 is the best way to determine how much of a price discount you need for E85 to make it economically feasible.

Conclusion

All the talk about ethanol being an inefficient energy converter is wrong. Moreover, the energy balance question is largely bogus. Whether you are concerned about weaning the U.S. from foreign oil, stopping global warming, or both, ethanol is better than gasoline and getting better every day.

References

Argonne National Laboratory. United States Department of Energy Laboratory. UChicago Argonne LLC. 18 June 2007.
Rendleman, C.M., Shapouri, H. “New Technologies in Ethanol Production.” USDA Agricultural Economic Report Number 842, 2007. 18 June 2007.
Lorenz, D., Morris, D. “How Much Energy Does it Take to Make a Gallon of Ethanol”. Institute for Local-Self Reliance, 1995.
The U.S. Dry-Mill Ethanol Industry. National Biobased Products and Bioenergy Coordination Office. United States Department of Energy. 18 June 2007.
Net Energy Balance of Ethanol Production Issue Brief. Ethanol Across America. Clean Fuels Foundation, 2004. 18 June 2007.
Energy Information Administration, Official Energy Statistics for the U.S. Government.

 

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