 Ethanol has a promising role to play in helping to solve many of the problems associated with gasoline use. While improving fuel economy is the most cost-effective, near-term solution for reducing global warming pollution, U.S. oil dependence, and Americans’ pain at the pump, there’s no one single cure for our problems. We’ll need cleaner fuels, more efficient vehicles, and smarter growth to truly clean up the transportation sector.
What is Ethanol?
Today’s Use of Ethanol
Global Warming Benefits and Impacts
Sustainable Production
Potential for Cellulosic Ethanol Production in the U.S.
What is Ethanol?
Most of the ethyl alcohol, or ethanol, used in vehicle fuel is produced by the fermentation of a sugar solution. In the United States, most ethanol is derived from the starches in corn kernels. Other types of plant material such as grasses, wood, and agricultural wastes can also be used to make “cellulosic” ethanol (named for the long chains of sugars that are the main component of plant cell walls).
Today’s Use of Ethanol
Nearly all of the ethanol used in the U.S. is blended into conventional gasoline. Ethanol use is on the rise in the U.S. According to the Renewable Fuels Association, demand for ethanol more than tripled between 2002 and 2007, from about 2 billion gallons per year in 2002 to over 6.5 billion gallons per year in 2007. In 2007, ethanol displaced about three percent of our gasoline use.
All of today’s gasoline-burning cars and trucks can use a blend of 10 percent ethanol (known as E10) more or less without any engine modifications. However, E10 can cause an increase in smog-forming pollution relative to conventional gasoline. To ensure no backsliding in air quality, gasoline specifications must be modified to burn clean on E10. Flexible-fuel vehicles (FFVs) can run on a fuel blend of up to 85 percent ethanol (known as E85).
Global Warming Benefits and Impacts
Because a gallon of ethanol contains less energy when burned than a gallon of gasoline, ethanol yields lower fuel economy than gasoline alone. But depending on how and with what feedstock it is produced, ethanol can have lower “lifecycle”—from seed to tailpipe—global warming pollution performance compared with an energy-equivalent quantity of petroleum fuel.
Today’s lifecycle emissions estimates do not necessarily include all potential sources. For example, if land is converted from forest to cropland, there can be a significant increase in global warming pollution. This effect is challenging to model, and most lifecycle analyses assume no emissions from land conversion. Similarly, there is conflicting data on emissions from fertilizer use, and more research is needed to accurately characterize all potential sources.
Most analyses indicate that corn ethanol delivers a 10 to 20 percent reduction in global warming emissions over its full lifecycle compared with gasoline. This reduction is modest because corn production requires a significant amount of fossil fuel inputs for farm operations and fertilizer production (generally natural gas). Corn production also generates a substantial amount of nitrous oxide, a global warming pollutant, as unused fertilizer breaks down in the field. In addition, many corn ethanol production facilities operate on natural gas; if new production facilities use coal instead, the emission benefits of corn ethanol could be reduced or eliminated.
Cellulosic ethanol can reduce lifecycle global warming emissions by as much as 80 to 90 compared with gasoline. Cellulosic materials require less fertilizer to grow and require less land in order to produce an equivalent amount of fuel. Additionally, the non-fermentable parts of the plant can be used as combustible fuel in place of fossil fuels.
Sustainable Production
If done wrong, the production of biomass for biofuels like ethanol could destroy habitats, worsen water or air quality, limit food production and even jeopardize the long-term viability of the biomass resource itself. The environmental impact of biofuels is comparable to certain agricultural crops. For example, the growing of corn has similar consequences whether the corn is grown for food, animal feed, or as a biofuel feedstock. The environmental impact is particularly high when virgin forestland is cleared for monocrop farming of current generation feedstock, such as corn. Next generation feedstock, such as cellulosic, offer a lower-impact alternative, especially if grown with smart farming practices, such as no or low-till, plant diversification, and lower pesticide and fertilizer use. As we expand our biofuels production, there must be adequate safeguards in place to ensure that fuels are produced in a manner that safeguards the environment.
Potential for Cellulosic Ethanol Production in the U.S.
The long-term potential for cellulosic ethanol production is significant, but key breakthroughs are needed to improve both crop yields and production efficiency. In particular, further advances are needed in order to cost-effectively liberate cellulose from the plant material and convert it into fermentable sugars.
U.S. Environmental Protection Agency estimates that by 2012, low carbon ethanol—like cellulosic—could displace 288 million gallons of gasoline—much less than one percent of our demand for gasoline. Congress has debated legislation that would increase cellulosic ethanol use up to 21 billion gallons by 2022. However, this would represent only eight percent of our gasoline demand in 2022, if we do not also take steps to improve fuel economy and reduce travel demand. As cellulosic ethanol production increases, it will also be important to ensure that the feedstocks are grown and harvested in a sustainable manner that protects wildlife habitats along with air, water, and soil quality.
Although the large-scale and long-term potential for corn ethanol production is limited, it will be an important part of the transition to even cleaner forms of ethanol. As of the end of 2007, roughly 20 to 25 percent of our corn crop was used for making ethanol, yet this displaced less than 3 percent of the gasoline we used for our cars and trucks. Even if we used all our corn to make ethanol, with nothing left for food or animal feed, we could only displace about 12 percent of our gasoline demand. Clearly, today’s corn ethanol is not a sufficient long-term solution to our oil dependence.
In the long term, renewable fuels like cellulosic ethanol will help reduce gasoline use and global warming emissions. But, in the near term, the greatest oil and consumer savings can be realized through improving the fuel economy of new vehicles. Such fuel efficiency gains will contribute to a more cost-effective shift to a sustainable ethanol future. |
