Hi-CAES: High Performance Compressed Air Energy Storage Elevated through High-Temperature Thermal Storage

Compressed Air Energy Storage (CAES) uses compressors to produce pressurised air while excessive power is available; the pressurised air is then stored in air reservoirs and will be released via a turbine to generate electricity when needed. Compared with other energy storage technologies, CAES has some highly attractive features including large scale, long duration, and low cost. However, its low round trip energy efficiency (the best CAES plant currently in operation has a 60.2% round trip efficiency) and low energy density cause major concerns for commercial deployment. The conversion of electricity to heat and storing the heat via thermal storage is a relatively mature and a highly efficient technology; but the conversion of the stored thermal energy back to electricity has a low energy efficiency (less than 40%) through (conventional and organic) Rankine cycles, thermoelectric generators, and recently proposed thermophotovoltaics.

The project aims to develop a Hi-CAES technology, which integrates the CAES with high-temperature thermal energy storage (HTES) to achieve high energy conversion efficiency, high energy and power density, and operation flexibility. The technology uses HTES to elevate CAES power rate and also convert high-temperature thermal energy to electricity using compressed air - a natural working fluid. The proposed technology is expected to increase CAES's electricity-to-electricity efficiency to over 70% and overall energy efficiency to over 90% with additional energy supply for heating and cooling. The proposed Hi-CAES will also increase the storage energy density and system power rate significantly. Meanwhile, the technology can convert the stored thermal energy into electrical power with a much higher energy conversion efficiency and lower system cost than current thermoelectrical energy storage technologies.

With the integration of HTES with CAES, the system dynamic characteristics and operation flexibility can be much improved in terms of charging and discharging processes. This will place Hi-CAES in a better financial position as it can generate revenue through certain high market value fast response grid balance service.

The goal of the project is to improve both the CAES efficiency and energy density considerably through the integration with a HTES system. The research will address the technical and scientifically challenges for realisation of the Hi-CAES system and societal challenges of deep power system decarbonisation.