In January, USDA researchers completed a five-year evaluation of another biofuel feedstock with the potential to make a serious dent in US petroleum usage. In the largest study to date, switchgrass has been shown to produce 540% more energy than was used to grow, harvest, and process it into cellulosic ethanol, while reducing greenhouse-gas (GHG) emissions by 94% when compared to gasoline.
USDA geneticist Ken Vogel commented that the study demonstrates switchgrass’s potential to be a major renewable biofuel that reduces GHGs and could “potentially displace 30 percent of current U.S. petroleum consumption.”
Key points from the study include:
- Researchers don’t expect switchgrass to replace corn fields, but see crop development occurring on marginal, highly-erodible lands.
- Ethanol yields on marginal land averaged 300 gallons per acre (corn-grain ethanol produces 350 gallons per acre).
- Biomass left over after converting switchgrass into cellulosic ethanol could be used to provide energy for the distilling and biorefinery processes, further adding to the fuel’s net energy balance. Comparatively, corn-grain ethanol typically uses natural gas or other power sources for processing.
- Experimental switchgrass strains currently undergoing testing could potentially produce 50% higher yields than those found in this study.
- Six cellulosic ethanol refineries are currently being constructed in the US, with partial funding from the DOE.
For comparison: soybean-based biodiesel offers about a 320% energy return, and grain-based ethanol produces about 125% more energy than it uses. Neither of these have the potential to displace more than a small fraction of US petroleum usage.
The study was conducted by researchers at the University of Nebraska-Lincoln and took place in North and South Dakota, and Nebraska.