Techno-economic assessment of a hybrid gas tank hot water combined heat and power system

Combined heat and power (CHP) systems with an integrated solid oxide fuel cell (SOFC) is a promising technology to increase overall efficiency of traditional residential combustion systems. One potential system is gas tank hot water heaters where partial oxidation of the fuel serves as a means of fuel reforming for SOFCs while producing thermal energy for heating water. In this study, a residential hybrid gas tank hot water heater with an integrated SOFC model was developed and a thorough techno-economic analysis was performed. Fuel-rich combustion characterization was performed at equivalence ratios 1.1 to 1.6 to assess synthesis gas production for the SOFC. The effect of fuel utilization and operating voltage of the model SOFC stack were analyzed to provide an in-depth characterization of the potential of the system. CHP and electrical efficiencies over >90% and >16% were achieved, respectively. The techno-economic analysis considers the four major census regions of the United States to evaluate regional savings based on respective utility costs and hot water demand. The results show the hybrid system is economically feasible for replacement of an electrical water heater with the longest payback period being approximately six years.