Greenhouse gas balance and resource demand of biogas plants in agriculture

For ten agricultural biogas plants, a detailed balance of greenhouse gas (GHG) emissions and cumulated energy demand was calculated. Compared with the reference system based on fossil resources, electricity production in the biogas plants avoids GHG emissions of 573-910 g CO2-eq/kWh(el) (CO2-eq, carbon dioxide equivalents; kWh(el), Kilowatt hours electrical energy). Without accounting for the substitution of electricity from the reference system, GHG emissions from electricity production in the biogas plants range from -85 to 251 g CO2-eq/kWh(el). With savings of 2.31-3.16kWh(fossil)/kWh(el) (kWh(fossil), Kilowatt hours primary energy from fossil energy carriers), the cumulated energy demand of the biogas plants was also much lower than for the fossil reference system. The reduction of direct methane emissions together with the efficient utilization of the heat from cogeneration and the use of animal waste as input material can improve the GHG balance of electricity production from biogas, substantially. Currently, a reliable estimate of the GHG emissions of electricity production from biogas can only be made based on individual monitoring data. The validity of GHG balances should be enhanced by providing reliable data on nitrous oxide emissions from energy crop cultivation, methane leakage from biogas plants and emissions from uncovered storage of digested residues.