Performance analysis of a two-stage thermal energy storage system using concrete and steam accumulator

This paper presents a thermal analysis of a two-stage thermal energy storage system, in which concrete is used in the high-temperature heat storage stage and steam accumulator is used in the low-temperature stage. To analyze the thermal characteristics of the whole system, a numerical simulation model for the two-stage thermal storage system was developed, based on the conservation principle of mass and energy. The results show that the performance of the high-temperature concrete storage unit depends greatly on the concrete conductivity and the distance between the neighboring steel tubes. Also, the steam discharging speed of steam accumulator directly affects the heat behavior inside the concrete block. The founded simultaneous decline in the energy quality level for the steam accumulator and the concrete system may benefit cascade utilization of thermal energy. Results of the investigation will assist in the optimum design of the thermal energy storage system used for solar thermal power plant.