Thermodynamic and exergy analysis of a combined pumped hydro and compressed air energy storage system
Highlights•A PHCA system can be incorporated with renewable sources such as wind and solar.•A thermodynamic and exergy model was developed to study a PHCA system performance.•Key parameters affecting the system performance were investigated and evaluated.•Exergy destruction for each system component was analysed and discussed.•Pump was identified as the most important component to improve the system efficiency.AbstractThe Pumped-Hydro and Compressed-Air (PHCA) is a new energy storage system which can be coordinated with renewable energy sources such as wind and solar. In this paper, a comprehensive thermodynamic and exergy model is developed to study the thermal characteristics of a combined Pumped-Hydro and Compressed-Air (PHCA) energy storage system. The effect of key parameters, including storage pressure, pre-set pressure, air-compression mode and pump/hydroturbine efficiency on system performance is investigated. The results showed that an optimum pre-set pressure existed to maximize energy storage level for a specific storage pressure. The storage pressure also showed a large effect on the energy storage level and work output. As the storage pressure increased from 4 to 16 MPa, the energy storage level and work output increased remarkably. Furthermore, the performance of a PHCA system was largely influenced by the air compression/expansion mode in the energy storage vessel. The PHCA system stored 10% more energy through an isothermal compression process than that through an isentropic air compression process. It generated 14% more work output through an isothermal expansion process than that through an isentropic air expansion process. The exergy analyses showed that exergy destruction in pump was about 15% higher than that in hydroturbine.