Comparison of energy and greenhouse gas balances of biogas with other transport biofuel options based on domestic agricultural biomass in Finland

Abstract

Biofuels have been promoted as a way to reduce greenhouse gas (GHG) emissions, but it is questionable whether they indeed do so. The study compared energy and GHG balances of transport biofuels produced in Finnish conditions. Energy and GHG balances were calculated from a life cycle perspective for biogas when timothy-clover and reed canary grass silages and green manure of an organic farm were used as a raw material. The results were compared with published data on barley-based ethanol, rape methyl ester (biodiesel) and biowaste-based biogas. The energy input for biogas was 22-37% of the output depending on the raw material. The GHG emissions from field-based biogas were 21-36% of emissions from fossil-based fuels. The largest energy input was used in the processing of the biofuels while most of the greenhouse gases were emitted during farming. The GHG emissions of the field-based biogas were emitted mainly from fuels of farming machinery, nitrous oxide (N2O) emissions of the soil and the production of ensiling additives. The energy efficiency was most sensitive to the methane yield, and GHG emissions to the N2O emissions. Biogas had clearly lower energy input and GHG emissions per unit energy output than domestic barley-based ethanol and biodiesel. © Agricultural and Food Science.