Exergy analysis and optimization of charging–discharging processes for cascaded latent heat storage system

The use of exergy analysis provides theoretical guidance for the cascaded latent heat storage system (CLHSS). However, the exergy analysis of the CLHSS charging–discharging processes is imperfect with two problems to be solved. One is the lack of exergy flow analysis, the other is the inaccurate expressions of the overall charging–discharging processes exergy efficiency. This paper aims to solve the above two problems. First, the exergy flow of the CLHSS charging–discharging processes was revealed, composed of one or more of the three exergy flow paths. Second, the overall exergy efficiency was derived by determining exergy produced and consumed. Only by satisfying the constraint that the exergy change of each PCM is equal to zero, the product of exergy efficiencies of charging and discharging processes can represent the overall exergy efficiency. On this basis, previous models that used the product of exergy efficiencies were modified by adding constraints. Compared to models without constraints, the model with constraints has more accurate and complete optimization results, which is conducive to the CLHSS stable operation. Finally, the model with constraints was adopted to guide the application of the CLHSS in the solar power tower. •Cascaded latent heat storage system (CLHSS) charge–discharge exergy flow is revealed.•The overall exergy efficiency and product of exergy efficiencies are distinguished.•The model that used product of exergy efficiencies was revised by adding constraints.•The revised model has more accurate optimization results and is recommended.•Application guidance of the CLHSS in the solar power tower system was provided.