A novel transcritical CO₂ energy storage system

To ensure grid frequency and power stability and realize bulk energy storage, a novel transcritical CO₂ energy storage system was proposed in view of the defects in the existing compressed air energy storage systems. The concept is based on taking liquid CO₂ as the storage media, thermal energy and cold energy as the main storage forms, so as to realize charging and discharging processes for wind power. Thermodynamic analysis and multi-objective optimization were performed and results showed that both round-trip efficiency and energy density increase firstly and then decline with the increase of discharging pressure at suitable charging pressure, which means that there exists an optimal discharging pressure. As charging pressure increases, round-trip efficiency declines while energy density increases. The key approach to improve the round-trip efficiency is to decrease the heat transfer temperature differences of cool storage unit, intercooler and reheater. The optimum round-trip efficiency and energy density are 50.4% and 21.7 kW·h/m³, respectively. The transcritical CO₂ energy storage system has advantages such as high energy density, high-efficiency and environment friendly, no geographical restriction, showing a promising potential for storing wind power in large scale.