Exergy and economic comparison between kW-scale hybrid and stand-alone solid oxide fuel cell systems

Abstract

Abstract Although hybrid solid oxide fuel cell (SOFC) microturbine systems generate power more efficiently than stand-alone SOFC systems, hybrid systems remain in the demonstration phase. This study compares a hybrid system's exergetic and economic performance with that of a stand-alone system. Both systems meet a university building's kW-scale power demand. The hybrid system operates at 66 % exergetic efficiency, and the stand-alone system operates at 59 % exergetic efficiency. Increasing the fuel cell's operating voltage increases the systems' exergetic efficiencies, and varying the fuel cell's temperature, pressure, and fuel utilization influences the systems' exergetic performances, though to a lesser extent. This study calculates the systems' life cycle costs. We find that the systems' life cycle costs depend significantly on the systems' operation. During baseline operation, the hybrid system costs less than the stand-alone system. After optimizing the systems during cogeneration operation, the hybrid system costs slightly more than the stand-alone system. Overall, our findings support hybrid systems' continued research and development; it is recommended that future work simulate hybrid and stand-alone systems under a range of thermal-to-electric ratios to reflect different building types and operation.