Dynamic Modeling of a Solid Oxide Fuel Cell Combined Heat and Power System With Thermal Storage for Commercial Building Applications

A dynamic model of an integrated solid oxide fuel cell (SOFC) combined heat and power (CHP) system has been developed. The model was developed by modifying a previously developed generic 5 kW simple-cycle SOFC system. Fuel cell model modifications include changes in methods and constants for estimating over-potentials to better simulate a modern anode-supported planar SOFC. In addition to scaling up and modifying the fuel cell model, a thermal energy storage (TES) tank, exhaust gas duct burner and hot water exhaust gas recuperator model were integrated into the system model. The fully integrated system model can effectively simulate an SOFC-CHP system and evaluate the system performance and efficiency in meeting building electricity and heating demand profiles. For the present effort, dynamic building electricity and heating data from a hotel operated in Orange County, southern California during the months of July and August 2008 were analyzed. Specifically, tradeoffs between SOFC performance and thermal energy storage have been investigated. The simulation results show that the SOFC-CHP system has the ability to follow the dynamic electrical load with appropriate system design and controls. Due to thermal power mismatch during electricity load-following operation, supplementary exhaust gas duct burner heat and/or a TES is required to independently dispatch the fuel cell power and meet the hotel heating demand. However, if the fuel cell is sufficiently sized, the system can achieve greater than 70% efficiency with only a small TES tank and without the need to fire the duct burner. The dynamic model and integrated SOFC-TES concept are shown to be useful for developing integrated CHP systems and to evaluate performance.