A novel solar hydrogen production system integrating high temperature electrolysis with ammonia based thermochemical energy storage

Abstract

In this paper, a novel solar hydrogen production system integrating high temperature electrolysis (using solid oxide electrolyzer cell) with ammonia based thermochemical energy storage is proposed for the first time. Without a significantly high concentration ratio, the thermochemical energy storage can upgrade relatively low-temperature solar energy to high-temperature reaction heat for high temperature electrolysis (HTE). Furthermore, thermal coupling of ammonia based thermochemical energy storage system, sCO2 Brayton cycle and HTE will result in substantially higher fuel production efficiency as compared to conventional low-temperature water electrolysis. A system model, including ammonia based thermochemical energy storage, sCO2 Brayton cycle and solid oxide electrolyzer cell (SOEC) system, has been developed using the Aspen Plus software implemented with user-defined Fortran subroutines. The models including reactors, sCO2 Brayton cycle and SOEC have been validated by comparing the model-generated results with the data from references. The effects of the endothermic reactor inlet temperature T2, charging loop ammonia mass flow rate ṁc, turbine inlet temperature T11 and current density J on the system performance have been investigated parametrically. The results show that the solar to hydrogen efficiency ηSTH increases with T2, T11 and J increasing. In addition, there is an optimum ηSTH by varying ṁc. Further, a maximum ηSTH = 26% has been obtained by optimizing the parameters in predefined ranges, which is 7% higher than the state-of-the-art of the solar HTE with TES. Based on a preliminary techno-economic analysis, the capital cost of the proposed system is estimated to be 9.28 $/kg H2, which is 18.9% lower than a typical photovoltaic based electrolyzer system. Therefore, the proposed system is economically feasible.