Energy and CO 2 balance of maize and grass as energy crops for anaerobic digestion

Abstract

Energy crops can be used to feed anaerobic digesters and produce renewable energy. However, sustainability of this option requires that it contributes to a net production of renewable energy and a net reduction of fossil CO 2 emission. In this paper, the net balance of CO 2 emission and renewable energy production is assessed for maize and grass energy crops produced in several agricultural systems relevant for Southern Belgium and surrounding areas. The calculated net energy yields are 8–25 (maize) and 7.4–15.5 (grass) MWh of renewable CH 4 per MWh of fossil energy invested, depending on the agricultural option considered. After conversion to electricity, the specific CO 2 emissions range from 31 to 104 kg CO 2 MWh electricity - 1 , depending on the case considered. This corresponds to a significant reduction in CO 2 emissions compared to the current reference gas-steam turbine technology which produces 456 kg CO 2 MWh electricity - 1 .