Energy balance of switchgrass grown for cellulosic ethanol in the Northern Plains, USA

Switchgrass (Panicum virgatum L.) is a potential, herbaceous feedstock for cellulosic ethanol in the USA. Estimates on switchgrass energy inputs and ethanol energy yields are highly variable and are largely based on small-plot research. A five-year, field-scale trial was completed on 10 farms in the Northern Great Plains to evaluate the energy balance for switchgrass grown for cellulosic ethanol. Energy balances were calculated using the energy and resources group biofuel analysis meta-model (EBAMM) model based on known farm inputs. Nitrogen fertilizer, diesel fuel, and herbicides accounted for 62, 17, and 10%, respectively, of average agricultural energy inputs. Net energy values averaged 21.6 MJ L^-1 with a range of 16.9 to 23.7 MJ L^-1 for the ten farms. The EBAMM model showed that switchgrass on average produced an estimated 13.5 MJ of ethanol for one MJ input of petroleum.