Corn ethanol directly emits an average of 51 percent less greenhouse gas than gasoline, as much as three times the reduction reported in earlier research, thanks to recent improvements in efficiency throughout the production process, University of Nebraska-Lincoln research shows.
A Journal of Industrial Ecology article (available online at
http://dx.doi.org/10.1111/j.1530-9290.2008.00105.x) outlines the research, conducted by an interdisciplinary team of UNL researchers, which evaluated dry-mill ethanol plants that use natural gas. Such plants account for nearly 90 percent of current production capacity.
This research is the first to quantify the impact of recent improvements throughout the corn-ethanol production process, including crop production, biorefinery operations and co-product use, said Ken Cassman, UNL agronomist who was part of the research team. Previous studies, which found ethanol to have a much smaller edge over gasoline in GHG emissions, relied on estimates based on corn production, ethanol plant performance and co-product use as they were seven years ago.
“Critics claim that corn ethanol has only a small net energy yield and little potential for direct reductions in GHG emissions compared to use of gasoline,” Cassman said. “This is the first peer-reviewed study to document that these claims are not correct.”
More recently built — and more efficient — plants now represent about 60 percent of total ethanol production and will account for 75 percent by the end of 2009, Cassman added. These newer biorefineries have increased energy efficiency and reduced GHG emissions through the use of improved technologies. Also, many are located near cattle feeding or dairy operations, which allows efficient use of the co-product distillers grains as cattle feed. For example, the distillers grains don’t have to be dried to facilitate long-distance travel; drying uses up to 30 percent of total energy use in the ethanol plant.
Also contributing to corn ethanol’s GHG performance are improvements in how the crop is grown, including improved crop and soil management, and better hybrids that help farmers achieve a steady increase in corn yields without having to increase fertilizer or energy inputs.
The result of these improvements: The ethanol industry currently is producing a fuel that is 48 to 59 percent lower in direct-effect lifecycle greenhouse gas emissions than gasoline. That’s two to three times the reduction reported in earlier studies that did not take into account recent advances in corn-ethanol production.
The net energy ratio, which averaged 1.2 to 1 in earlier studies, is 1.5-1.8 to 1 in the recent research, Cassman said. That means that for every unit of energy it takes to make ethanol, 1.5 to 1.8 units of energy are produced as ethanol.