LAUSR

Abstract Hybrid power plants which combine a micro gas turbine with solid oxide fuel cells, are projected to reach very high electric efficiencies. Powered by biogas, they have the potential to become an important pillar for a future CO2-neutral energy mix. However, to compensate the fluctuating energy yield of wind turbines and photovoltaic power plants, they should also provide a wide operating range. While previous numerical studies show that this is the case for natural gas powered hybrid power plants, the impact of biogas utilization on the operating range is still unknown. In the present study, a detailed numeric model of the hybrid power plant demonstrator being constructed at the DLR is presented. The model is used for an in-depth investigation of the operating limits using biogases with various methane contents. The influence of fuel cell operating limits, like the stack temperature, minimal cell voltage and maximal fuel utilization ratio, on the hybrid power plant operating range are discussed. While the results show a strong correlation between methane content and operating range, a power output reduction of 33% is still feasible for methane contents as low as 60 vol%. Furthermore, knowing the operating range of the hybrid power plant is crucial for the design of the plant components. Therefore, in a final step, the operating conditions for the fuel cell off-gas combustor are derived for the respective operating ranges.