Cyclic thermal characterization of a molten-salt packed-bed thermal energy storage for concentrating solar power

Molten-salt packed-bed thermocline thermal energy storage (TES) is identified to be a cost-competitive TES type for concentrating solar power (CSP). The present study reveals the system-level cyclic thermal characteristics of the molten-salt packed-bed TES with typical configurations on two levels of investigation, based on a one-dimensional enthalpy-method dispersed-concentric (D-C) model. Firstly, a three-stage operation scheme is proposed to evaluate the thermal performance of the introduced partial charge cycles and the subsequent full charge cycles, under ideal operating conditions. The 'partial charge effect' of the packed-bed TES is identified by evaluating the variations in thermocline development and energy storage/release capacity. The results show that the introduced partial charge cycles can generally lead to a thermocline degradation, and then impact the energy store/release capacity in the subsequent full charge cycles. The configurations containing encapsulated PCMs are of greater resistance and stronger recoverability to the variation in energy storage/release capacity. Then the study is extended to investigate the thermal performance of a 100 MWe CSP plant integrated with a well-sized packed-bed TES system, over a 14-day practical operation based on variable energy collections. Deviations between the designed and practical energy store/release capacity of the systems are evaluated. The results indicate that of the sensible-heat and the single-layered latent-heat packed-bed TES present significant shortages in energy storage capacity during the operation, which can lead to energy collection discards. Overall, the obtained results present a new perspective to evaluate the availability of the packed-bed TES system for CSP plants.