Thermodynamic analysis of a novel energy storage system based on compressed CO2 fluid

Because of rapidly growing renewable power capacity, energy storage system is in urgent need to cope with the reliability and stability challenges. CO₂ has already been selected as the working fluid, including thermo‐electrical energy storage or electrothermal energy storage systems and compressed CO₂ energy storage (CCES) systems. In this paper, a CCES system based on Brayton cycle with hot water as the heat storage medium is proposed and analyzed. Thermodynamic model of the system is established for energy and exergy analysis. Sensitivity analysis is then conducted to reveal effects of different parameters on system performances and pursue optimization potential. At a typical transcritical operation condition, round trip efficiency is 60% with energy density of 2.6 kWh/m³. And for the typical supercritical operation condition, the round trip efficiency can reach 71% with energy density of 23 kWh/m³. High round trip efficiency and energy density, which is comparable with those of compressed air energy storage systems, thermo‐electrical energy storage (electrothermal energy storage) systems, and other CCES systems, lead to promising prospect of the proposed system. Copyright © 2017 John Wiley & Sons, Ltd.