Exergy assessment and optimization of a cogeneration system based on a solid oxide fuel cell integrated with a Stirling engine

•A novel cogeneration system driven by a SOFC and Stirling engine is proposed.•Energy and exergy assessments are reported of a novel cogeneration system.•The energy efficiency of the combined system can be achieved 75.88%.•The highest exergy destruction occurs in the air heat exchanger. A cogeneration system based on a methane-fed solid oxide fuel cell (SOFC) integrated with a Stirling engine is analyzed from the viewpoints of energy and exergy. The effects on the system performance are investigated of varying four key system parameters: current density, SOFC inlet temperature, compression ratio and regenerator effectiveness. The energy efficiency of the combined system is found to be 76.32% which is about 24.61% more than that of a stand-alone SOFC plant under the same conditions. Considering exergy efficiency as the only objective function, it is found that, as the SOFC inlet temperature increases, the exergy efficiency of the cogeneration system rises to an optimal value of 56.44% and then decreases. The second law analysis also shows that the air heat exchanger has the greatest exergy destruction rate of all system components. The cooling water of the engine also can supply the heating needs for a small home.