Development of a combined pumped hydro and compressed air energy storage system

Renewable energy resources are of great attention by many countries. However, volatile and intermittent nature of renewable energies has made their directly connect to the grid very challenging and costly. Therefore, it is essential to couple a renewable energy resource with an energy storage technology. Among different types of energy storage systems developed so far, compressed air energy storage (CAES) is a large-scale energy storage system which has distinguished advantages over other types of energy storage systems; such as large energy storage capacity, long operation time and short response time. Currently, there are two called conventional or Diabatic CAES (D-CAES) plants in operation one of which is in Huntorf (Germany) and the other is in McIntosh (USA). However, the main drawback of these D-CAES plants is their low cycle energy efficiency primarily due to a large energy loss during the system operation. To minimise the energy loss and improve the system performance, the structure of D-CAES evolved and new classifications of the CAES system were developed. In the present thesis, a wide literature review is firstly performed to obtain a broad overview of recent developments in various classifications of CAES systems and identify the research gap in this technology. Adiabatic CAES (A-CAES) is one of the main types of CAES systems. However, one of the most challenges associated with the A-CAES is variation of the air pressure and temperature during actual cyclic operation of the system particularly through expansion when the air flows out of the storage cavern. In this research, a comprehensive thermodynamic model is developed and validated with an experimental work to study the dynamic operational behaviour of a low-temperature A-CAES system. A sensitivity analysis is then performed to investigate the system performance under various operating conditions. The obtained results from the conducted analysis show that the system cycle efficiency is quite low compared to other types of energy storage systems. Therefore, there is a strong need to propose and develop a new energy storage technology which resolves the problems associated with the CAES system. The performed study on the A-CAES system and the pumped hydro concept are employed to develop the configuration and working principles of a combined Pumped-Hydro and Compressed Air (PHCA) energy storage. A comprehensive thermodynamic and exergy model is then developed to identify key parameters of the PHCA system and investigate its performance under two extreme isothermal and isentropic air compression/expansion in the storage vessel. Key parameters of the system include the pre-set pressure, storage pressure, air compression/expansion mode in the storage vessel, and pump/hydro turbine efficiency. The system performance is also characterised by the total input/output works, energy storage level in the system, overall cycle efficiency, and exergy destruction in main components of the system. The exergy model is then applied to evaluate the performance loss due to exergy destruction at each system component and identify their inefficiency under different operating conditions. In a PHCA energy storage system, energy is stored in a storage vessel. The dynamic fluid flow and heat transfer mechanism inside the storage vessel has a determining effect on performance of the PHCA system. In this research, the dynamic flow and heat transfer is simulated and analysed in a three-dimensional cylindrical storage vessel using a multiphase Volume of Fluid (VOF) and turbulence k ‚Äöv†v¿ ˜í¬µ models. Momentum and energy equations are solved in a prescribed physical domain which is, in this study, a cylindrical storage vessel with an inner diameter of 60 cm and height of 100 cm. The numerical simulation is performed for one continuous operational cycle of the PHCA system. The results are presented for a wide range of governing parameters including the pre-set pressure, storage pressure, charging and discharging flow rates. The presented research provides a good understanding of performance of the PHCA system under different operating conditions. Also, this PhD thesis provides researchers and engineers with useful information for the primary system design and optimization based on the grid requirements and limitations. It also shows a bright view about applicability and practicality of the PHCA system in the Australia energy storage market.