Corn ethanol directly emits an average of 51% less greenhouse gas (GHG) 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 (UNL) 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% 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 coproduct use, says 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 coproduct 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 says. "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% of total ethanol production and will account for 75% by the end of 2009, Cassman adds. 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 coproduct 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% 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 48-59% lower in direct-effect lifecycle GHG 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 says. 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.
Even more striking is the corn ethanol's potential to replace oil. This new study estimates that 10-19 gal. of ethanol are produced for every gallon of petroleum used in the entire corn-ethanol production life cycle. The range in the ethanol-oil replacement value, as well as the ranges measured for net energy efficiency and GHG emissions reduction, are due to differences in crop-management practices and ethanol plant performance.
The findings are key to corn ethanol's long-term viability, Cassman says, because the industry has been justified, in part, by the assumption that GHG emissions would be reduced as ethanol replaces petroleum-derived gasoline.
The research is a component of a regional, multi-university research initiative known as NC506, to assess the economic and environmental sustainability of the rapidly expanding Midwestern corn ethanol industry. This project is funded by the USDA and the North Central Bioeconomy Consortium. Other sources of funding include the Western Governors Association, Environmental Defense, the Agricultural Research Division at UNL and the Nebraska Center for Energy Sciences Research.
Researchers used the UNL-developed Biofuel Energy Systems Simulator, or BESS, to make their calculations. This software is available for download at http://www.bess.unl.edu. BESS analyzes energy yield and efficiency, GHG emissions and resource requirements for individual biofuel production systems. This "seed-to-fuel" tool quantifies lifecycle carbon savings and environmental impact of individual biofuel systems. It factors in energy use and GHGs from crop production, ethanol conversion, coproduct use and transportation.
The study did not take into account indirect land use change, because there is not yet a scientific consensus about how to estimate the magnitude of these effects as a component of the GHG intensity of biofuels.