Pumped thermal energy storage systems integrated with a concentrating solar power section: conceptual design and performance evaluation

A novel Pumped Thermal Energy Storage (PTES) system thermally integrated with a Concentrating Solar Power (CSP) plant is proposed and investigated. The two sections operate with the same working fluid, share several components and can operate simultaneously or independently of each other. A Thermal Energy Storage (TES) system composed of three thermocline packed-bed tanks is included. Specific mathematical models were developed to simulate the performance of the integrated PTES-CSP plant under nominal conditions and to evaluate the thermal profiles of the TES tanks. As a case study, an integrated PTES-CSP system characterized by a nominal power of 5 MW with a nominal storage capacity of 4 equivalent hours was considered. The influence of the main design parameters, namely the pressure ratio and the operating temperatures of the TES system, on the main performance indices was investigated. The results demonstrated that the exergetic roundtrip efficiency of the integrated plant reaches a maximum for a pressure ratio of about 5.2. A sensitivity analysis on the solar receiver temperature and turbomachinery polytropic efficiency and maximum allowable temperatures was also conducted. Finally, a feasible design for the PTES-CSP system characterized by an exergetic roundtrip efficiency of about 60% was proposed.