Comparative Thermodynamic and Economic Analysis of Closed and Semi-Open Compressed Carbon Dioxide Energy Storage Systems

Long-duration energy storage (ES) has aroused widespread concern by virtue of its potential in renewable energy consumption and the achievement of carbon neutrality goals. Compressed Carbon Dioxide Energy Storage (CCES) works as one of the most attractive technologies for long-duration ES. However, efficient and economical CCES systems are still lacking. In the present study, two novel CCES systems have been proposed, namely Closed-CCES and Semi-open-CCES. Under typical design conditions, the Closed-CCES system achieves a cycle efficiency of 62.25%, whereas the Semi-open-CCES system, featuring simultaneous cooling, heating, and power outputs, attains a superior energy storage density (ESD) of 7.38 × 107 J·m−3. Compared with comparable energy storage systems, the two proposed systems exhibit distinct advantages in cycle efficiency and energy storage density, respectively. As noted by exergy analysis, the key loss source of Closed-CCES is the heat exchanger HE2, while the loss of Semi-open-CCES is mainly concentrated in the thermal storage device HFT1. Sensitivity analysis shows that ambient temperature and thermal storage pressure slightly affect the performance of both systems, while heat exchanger efficiency impacts the performance of Closed-CCES more significantly. Economic assessments reveal that both systems outperform conventional technologies in levelized cost of electricity (LCOE). The Closed-CCES system demonstrates superior economic viability with a lower LCOE of 0.0808 $/kW·h versus 0.0985 $/kW·h for the Semi-open system, with the advantage persisting in various operational scenarios. Research results provide a basis for the practical engineering implementation of CCES technology, contributing to the broader pursuit of long-duration energy storage solutions for carbon neutrality.