Greenhouse gas balance and resource demand of biogas plants For ten agricultural biogas plants, a detailed balance of greenhouse gas emissions (GHG) and cumulated energy demand (CED) was calculated. Compared to the reference system based on fossil resources, electricity production in the biogas plants avoids GHG emissions of 573 to 910 g CO 2-eq •kWh el-1. Without accounting for the substitution of electricity from the reference system, GHG emissions range from-85 g to 251 g CO 2-eq •kWh el-1.
... CO 2-eq •kWh el-1. With savings of 2.31 to 3.16 kWh fossil •kWh el-1 , the CED of the biogas plants was also much lower compared to the fossil reference system. Abstract Landtechnik 65 (2010), no. 3, pp. 208-212, 5 fi gures, 1 table, 7 references ■ The primary objective of producing energy from biogas is the reduction of the use of fossil energy carriers and associated emissions of greenhouse gases. On this background, actual greenhouse gas balances and cumulated energy demand of ten biogas plants with different designs were determined, also to check whether there is room for improvement. Modeling of real-world biogas plants Using the software umberto ® , a computer-based model for calculating material and energy fl ows for biogas plants and upstream agricultural production processes was developed. The goal of this model is to determine greenhouse gas and energy balances for individual biogas plants in reality. The model covers all processes that are relevant for energy production from biogas and their associated material and energy fl ows. To do this, the process of biogas production and utilization was subdivided into the following sections: Production, transport and ensilage of energy crops and ■ transport of animal manure, operation of biogas plant, ■ treatment of digested residue, ■ construction of biogas plant and ■ upstream processes (supply of electricity, fuel and mine-■ ral fertilizer). To determine overall greenhouse gas emissions, all relevant emissions that leave the balance envelope were added up. The cumulated energy demand includes the primary energy content of all fossil energy carriers that are supplied from outside of the balance envelope [1; 2]. The main product of the biogas plants that were analyzed is electrical energy. Therefore, all material and energy fl ows were specifi ed per one kilowatt hour of electrical energy fed into the grid. Beside electrical energy, thermal energy and fertilizer are produced. In the material balance, these products were treated