Studies on long-term and buffer modes of operations of a thermal energy storage system using coupled metal hydrides

Abstract

Metal hydride based thermal energy storage systems have attracted great attention due to their compactness and wide operational range. In long-term mode of operation, thermal energy is stored for long durations, whereas in buffer mode the heat storage is for immediate consumption, usually to cater for load fluctuations. This paper investigates a thermal energy storage system consisting of Mg2Ni-LaNi5 pair of metal hydrides in long-term and buffer modes of operation. Two inter-connected cylindrical reactors are simulated for multiple operating cycles using COMSOL Multiphysics®. The variations in porosity and density of hydride beds with hydrogen concentration during charging and discharging processes are considered. The effects of heat source temperature and the hydrogen storage bed temperature on the thermal performance of the system are investigated. The influence of hydrogen storage bed temperature is more significant in buffer operation than in long-term mode operation. With the heat source at 300 °C, the system achieved a storage density of 532.64 MJ m−3 with 67.8% and 430.28 MJ m−3 with 91.2% in long-term and buffer modes, respectively.