Impact of operational and design variables on the thermodynamic behavior of a simulated 500 kw ng-fueled solid oxide fuel cell stack

•Exergy efficiency and power-to-heat ratio used as thermodynamic performance indices.•Operational and design variables are varied within experimental ranges.•Anode recycle gas improve substantially the exergy efficiency of an SOFC stack.•Variation of anode gas diffusivity increases the SOFC stack exergy efficiency.•Power-to-heat ratio provides key results for designing hybrid energy systems.