tri-generation (Base SS-b) and purification and upgrading biogas to biomethane coupled with small-scale CHP unit (Base LS-B(U)), respectively. These are underlined by the technical viability of
CHP (Base SS-b) compared to Stirling engines (Base SS-d) which can only be deployed in small modular units rated at 30e200 kW (Pöschl et al., 2010). The results indicated that biogas utilization with fuel cell technology (Base LS-D(U)) may be viable both with respect to energy balance (Pöschl et al., 2010) and to mitigation of environmental emissions (Fig. 5). However, fuel cell technology considered is still at experimental stage and the accurate potential will be clearer after commercialization (Poeschl et al., 2010).