Treibhausgas-Emissionen in der deutschen Landwirtschaft

Abstract

This monograph is concerned with different aspects of green house gas (GHG) emissions in agriculture. The first part summarizes the total amount of GHG emissions and analyses them regarding their composition. A differentiation is made between the emissions which are already linked to agriculture (source group agriculture: digestion , manure-management and agricultural soils ) within the National Report on GHG Emissions and those which can be counted primarily in addition to agriculture ( energy and land use and land use change ). Depending on which database is used, agriculture is participating in emitting green house gases with 6.3% or 11.1% of total German GHG emissions in 2004. This means that agriculture is an important polluter. The development of GHG emissions in agriculture compared to the year 1990 is -18.5% for the source group agriculture. This means that the source group has reduced more emissions than the average (-17.5%) over all domains published within the National Report. Regarding the sources energy and land use and land use change in addition emission reduction is -16.4% in the same period and thus worse than the average. Moreover, realized emission reductions are predominantly based on structural changes, less on systematical measures. This fact raises the question how agriculture can make a contribution to the reduction of GHG emissions in future particularly with regard to higher aims in climate politics.For this reason the second part of the monograph identifies capacities for the reduction of GHG emissions by using available agricultural biomass for energetic purposes. Due to the heterogeneity of biomass and the variety of its possible products, a lot of technical processes concerning the conversion of biomass into energy exist in practice. Since all of them have different emission factors the derivation of realistic reduction capacities is a nontrivial problem. This work restricts the problem by combining existing biomass with those technologies which provide largest benefit concerning the reduction of GHG emissions. Thereby it is possible to evaluate the maximum contribution of GHG reductions from biomass usage in agriculture in Germany, which aggregates up to 50,341 Gg CO2-equivalent. This means that 78.3% of the emissions from the source group agriculture in 2004 could be compensated if biomass was used within those technologies which produce the largest benefit. In this regards the subsidy of energy crops in biogas plants based on the Erneuerbare Energien Gesetz (renewable energy law) in Germany should be reviewed because there they do not produce the largest benefit. Energy crops should be applied to replace solid fuels instead. Since in practice several biogas plants are already using energy crops as input material without having an option for alternatives, the question raises how this fact can be improved for the future regarding climate protection.Therefore the third part of this monograph analyses the possible emission reductions of different technologies for converting biogas into energy. Objects of investigation are existing technologies like block heat and power plants or direct gas feeding into public gas distribution system as well as future technologies like the application of biogas in different types of fuel cells. Although direct gas feeding has a better ratio concerning the conversion of primary to secondary energy the GHG reduction capacity is much less compared to technologies of cogeneration. The reason for this is that the production of electricity has much more effect on GHG emissions than the production of heat. This is to be seen when comparing the emission factors of certain reference systems used in this part like condensing boilers running with natural gas (253 gCO2/kWhheat), gas steam power plants (432 gCO2/kWhel) and the average emissions factor of German power production (653 gCO2/kWhel). The more electricity is produced by a conversion technology based on biogas, the higher is its GHG reduction capacity. Direct gas feeding is not the most efficient way of using biogas in matters of climate protection considering that only 13% of the natural gas in Germany is used for electric purposes and considering that replacing natural gas by biogas means that the part of fossil fuels with lowest emissions is replaced. Direct gas feeding is not even then the most efficient way of using biogas if there is a consumer at the other end of the public gas distribution system who theoretically uses the injected biogas for running cogeneration systems. The conditioning of biogas in order to feed public distribution combined with additional heat source for running the fermenter of the biogas plant is worse for efficiency. Considering ecological standpoints local heat and power production next to the fermenter is the most efficient way of using biogas in matters of climate protection. This can only be improved by using more efficient systems like fuel cells instead of existing block heat and power plants.