Performance evaluation and optimisation of a multistage wave-driven compressed air energy storage system

The abundant yet intermittent nature of ocean wave energy necessitates efficient storage to ensure a reliable power supply. Wave-driven compressed air energy storage (W-CAES) is a promising solution; however, conventional single-stage W-CAES designs exhibit limited energy capture and low efficiency. To address these limitations, this study proposes a multistage W-CAES system and develops an integrated model for comprehensive performance evaluation. Thermodynamic and energy flow analyses are systematically conducted to optimize the design. Additionally, a comparative evaluation is performed to examine the influence of key parameters, such as storage pressure and number of stages, on overall performance. Results indicate that increasing the number of compression stages significantly improves both capture factor and round-trip efficiency under equivalent storage conditions. In particular, a three-stage W-CAES achieves a capture factor of 9.1 % (versus 1.46 % for a single-stage) and a round-trip efficiency of 70.01 % (up from 64.53 %) at the same wave condition and storage pressure, demonstrating the benefits of the multistage approach. A Tasmanian case study demonstrates feasibility: 500 two-stage units could offset up to 20 % of Tasmania's imported energy, depending on seasons. These findings highlight the enhanced performance of multistage W-CAES and its potential to make significant contributions to renewable energy integration.