Multi-functional three-phase sorption solar thermal energy storage cycles for cooling, heating, and heat transformer

Abstract Thermal energy storage based on sorption method is attractive in view of energy storage density, storage period, and flexibility. Three-phase sorption thermal energy storage is advantageous from high energy storage density, but its temperature lift is low. Besides, further energy storage density enhancement is needed to make the storage system more compact. In this paper, multi-functional three-phase sorption thermal energy storage cycles are proposed to achieve a higher temperature lift and energy storage density simultaneously, in which different applications can be evident including interseasonal heating, combined cooling and heating in summer, and heat transformer in summer and winter. The performance of the proposed cycles for three operating modes is evaluated analytically with a working pair of LiCl/H2O, due to its high absorption and crystallization enthalpy. Results showed that the multi-functional three-phase sorption thermal energy storage cycles obtained a temperature lift of 65°C and an energy storage density up to 1307 Wh/kg, which cannot be realized with a conventional three-phase cycle. Moreover, a combined cold and heat storages at 15°C and 60°C, respectively, and discharging temperature more than 100°C are achieved. With these proposed cycles, a wider range of applications could be expected for three-phase sorption thermal energy storage.