Justification of CO₂ as the working fluid for a compressed gas energy storage system: A thermodynamic and economic study

The compressed carbon dioxide (CO₂) energy storage (CCES) system has been attracting more and more attentions in recent years. The CCES system leads the way of green solutions to accommodating the intermittency of renewable power generation systems in a large-scale energy storage pattern. Particularly, the usage of CO₂ as the working medium for CCES successfully offers a green solution to massive carbon capture and storage. This paper aims to further analyze the applicability and feasibility of a novel CCES system with the merit of efficiently and economically utilizing pressure energy and thermal energy. Thermodynamic and cost evaluation on the energy conversion cycle were carried out. Genetic algorithm was employed to perform multi-objective optimization on the novel energy conversion cycle with thermal energy storage towards maximizing exergy efficiency and economic profits. Results reveal that the net output power monotonously increases with turbine inlet temperature, but the unit product cost monotonously decreases with turbine inlet temperature. The multi-objective optimization recommends a 60.5% for the overall exergy efficiency and 0.23 $/kWh for the unit product cost. Moreover, scattered distribution of decision variables suggests always a higher outlet pressure for compressor.