Background: The German energy transition strategy calls for a reform of the German energy sector. As a result, the Germany Renewable Energy Sources Act (EEG) was passed in 2000 and is widely regarded as successful legislation for promoting bioenergy development. More than 1,000 biogas plants were constructed in Central Germany (CG) between 2000 and 2014. Despite this, few studies have been conducted for this period that systematically investigate how environmental, social and economic factors, as well as various EEG amendments have impacted biogas production and what the environmental consequence of biogas production development in CG have been.
Methods: The impacts of environmental, social and economic factors and different EEG amendments on biogas production decisions in CG were quantified using multivariate linear regression model and the event study econometric technique. A GIS-based spatial analysis was also conducted to provide insight into the changes to agricultural land use that resulted from the development of biogas plants during the EEG period.
Results: The main finding was that the income diversification effect resulting from biogas production was the most important factor in a farmer’s decision to adopt biogas production. In addition, all of the EEG amendments had a significant influence on the adoption of biogas production, however EEG III and IV, which tried to promote small-scale plants, were unable to reduce the average size of the plants constructed in these two amendment periods. From a landscape perspective, there was a striking increase in the cultivation of silage maize in CG from 2000 to 2014. Silage maize was intensively cultivated in regions with a high installed biogas plant capacity. Since the first EEG amendment, permanent grassland area slightly increased while arable land area declined in CG.
Conclusions: The adoption of biogas production in CG was strongly driven by economic incentives for the farmers, more precisely, by the incentive to diversify their income sources. In addition to increase the subsidy, future EEG amendments should find new measures to encourage the adoption of small-scale biogas plants, which had been unsuccessful in EEG amendments III and IV.