Potential of different Sorghum bicolor (L. moench) varieties for combined ethanol and biogas production in the Pannonian climate of Austria

The objective of this study is to estimate the energetic yields of a combined ethanol and biogas production from three different sorghum varieties, and to compare them to a similar estimate for maize in order to demonstrate the suitability of sorghum as an alternative biomass source. The sorghum varieties “SG1” (Sugargraze I) and “SG2” (Sugargraze II), which produce fermentable sugars, as well as the grain variety “C” (Chopper), which produces starch, were grown on experimental plots in eastern Austria. The harvested biomass was analysed for its contents of cellulose, hemicellulose, lignin, crude protein, crude fats, starch and sugar. For the calculation of the energy output, ethanol and biogas yields were calculated corresponding to accepted standard methods. The potential of sorghum for energy production has been demonstrated. The highest energy outputs were achieved by the SG1 and the C varieties, delivering approximately 150 GJ ha−1 and 156 GJ ha−1. Compared to data obtained from different maize varieties in the same year and under similar conditions, this means an equal or even increased energy output per hectare. The SG2 variety only yielded 121 GJ ha−1 worth of ethanol and biogas. Bioethanol and biogas production were unequally distributed between sugar and starch varieties: SG1 provided 70% of its energy output as methane and the rest as bioethanol, whereas the grain variety C yielded 46% methane and 54% bioethanol.