A new study by California researchers challenges claims that substituting ethanol for gasoline consumes more energy than it creates -- an argument that has dogged ethanol programs and their supporters for more than a decade.
However, the report also concludes that while ethanol made from corn -- the type that dominates the market today -- can sharply reduce overall petroleum use, it provides little reduction in greenhouse gas emissions compared with regular gasoline.
A string of studies on the topic have either come to contradictory conclusions or differed substantially over the amount of energy gained by using ethanol in place of other fuels. Researchers make that calculation by comparing the energy in ethanol to the amount of energy used in its production -- accounting for such things as the fuel used to harvest and process corn.
But in the new study, to be published today in the journal Science, lead author Alex Farrell and five other UC Berkeley researchers claim to have resolved the nagging "net energy" question surrounding ethanol.
The key, according to Farrell, is properly accounting for the byproducts of ethanol production, which include corn oil and animal feed. With that factored in, he said, "you gain about 20% more energy in the ethanol than you required in fossil energy to produce it."
The study's findings on which kinds of ethanol hold the most promise for reducing smog could influence California's developing plan to cut greenhouse gases. It could also damp enthusiasm for corn-based ethanol amid a nationwide move to increase the use of renewable fuels.
Farrell said the new study found that corn-based ethanol only reduces greenhouse gas emissions by 13%, but the fuel's effects on emissions varies depending on what it's made from. The study found that ethanol made from plants such as willow trees and switchgrass "offers large reductions in greenhouse gas emissions."
What that means, he added, "is that if California wants to reduce greenhouse gases by using ethanol, it's going to have to pay attention to how it's made."
The findings are of interest to the California Air Resources Board, the agency behind the state's formulas for cleaner-burning fuel and the group that will help determine how to cut greenhouse gases. In California, gasoline contains about 6% ethanol by volume and the state consumed more than 900 million gallons of ethanol in 2005 -- about a third of the nation's overall use.
"Anything that takes some of the controversy away from the benefits and dis-benefits of ethanol and what it really does will help us in our regulatory process because there would be fewer things we'd have to argue about," said Michael Scheible, deputy executive director at the air resources board.
Farrell's group reviewed six previous studies, including two produced by longtime ethanol critics David Pimentel, a professor at Cornell University, and by Tad W. Patzek, a fellow UC Berkeley professor. Pimentel and Patzek determined that making ethanol used up more energy than it produced, but Farrell said their work "incorrectly ignored co-products and used some obsolete data."
The professors "have done a very great service by asking the right question, which is, 'Can agricultural processes produce a fuel that is good for the environment?' " Farrell said. "We disagree slightly with their answer."
Patzek and Pimentel were not available for comment Thursday.