Changes in greenhouse gas balance and resource demand of biogas plants in southern Germany after a period of three years

For five agricultural biogas plants with a high share of energy crops in the input material a detailed balance of greenhouse gas emissions (GHG) and cumulated energy demand (CED) was calculated for the years 2007 and 2010. The results vary considerably between plants and over time. In 2010 compared with 2007 all of the five biogas plants reduced their impact on climate change and four of them also reduced their consumption of fossil energy. The strongest influence was from the enhanced utilization of surplus heat energy whereas variations of environmental impact due to direct emissions from the biogas plants were less distinctive. Compared with a reference system based on fossil resources electricity production in the biogas plants avoided GHG emissions of 603 g to 940 g carbon dioxide equivalents (CO2-eq)center dot kilowatt hours electrical energy (kWh(el)(-1)) and saved 2.48 to 3.23 kilowatt hours primary energy from fossil energy carriers (kWh(fossil))center dot kWh(el)(-1) CED (results for 2010).