Compressed air energy storage based on variable-volume air storage: A review

Compressed Air Energy Storage (CAES) is an emerging mechanical energy storage technology with great promise in supporting renewable energy development and enhancing power grid stability and safety. Conventional CAES typically utilize constant-volume air storage, which requires throttling to release high-pressure air. That results in a significant amount of air being trapped in the storage chamber, leading to low effective air storage density and high storage costs. In contrast, using variable-volume air storage allows for the entire air release by volume displacement, improving storage space utilization and significantly reducing storage costs. Meanwhile, the air can maintain a constant pressure (isobaric) during the volume displacement process, resulting in higher roundtrip efficiency than conventional CAES. As a result, CAES based on variable-volume air storage (VS-CAES) has sparked significant interest among researchers. This work comprehensively reviews various forms of VS-CAES systems, categorizing them based on their technical features. A detailed investigation of each type of VS-CAES system is conducted, summarizing their design concepts, structural characteristics, operational processes, performance advantages, challenges, and insight into future development prospects. This paper presents a comprehensive review and summary of the various reported VS-CAES systems for the first time, providing valuable reference for the further development and application of VS-CAES technologies.