Energy and exergy analysis of a novel pumped hydro compressed air energy storage system

Abstract

Many pumped hydro compressed air energy storage systems suffer from defects owing to large head variations in the hydraulic machinery. To solve this problem, this study proposes a novel pumped hydro compressed air energy storage system and analyzes its operational, energy, and exergy performances. First, the composition and operating principles of the system are analyzed, and energy and exergy models are developed for each module. Second, the operational characteristics of each module during the charging and discharging processes are analyzed. Finally, the energy and exergy performances of the system in single- and multi-cycle charging and discharging processes are revealed. The results show that the water pressure potential energy transfer module (module 2) effectively converts the pressure variation of nearly 1.6 MPa in the air storage tank to a head variation of 58.5 m during pumping and 48.2 m during power generation of the pumped storage unit. The electrical energy waste and exergy losses in module 1 are the highest, reaching 39.0% and 53.3%, respectively. After a single cycle, the efficiency, exergy efficiency, and energy storage density of the proposed system reach 59.0%, 70.1%, and 0.255 kW h/m3, respectively. After multiple cycles, the average efficiency increases to 62.5%.