A novel grid-scale Carnot battery energy storage system: Heat integration optimization and performance evaluation

A novel Carnot battery system has been proposed in this study, featuring a deep integration of retired coal-fired power plant and pumped thermal energy storage, with the aim of improving overall system performance and facilitating the low-carbon transition of the power grid. The system adopts a temperature-zone matching principle to couple multiple components. A compression heat pump subsystem is introduced to capture ambient low-grade thermal energy, thereby elevating the operational temperature of the charging cycle. Furthermore, by incorporating the high-pressure heater bypass operation strategy alongside the Solar salt-Hitec salt hybrid system, the system achieves substantial expansion of its heat release temperature range during discharging. These innovative design features enable a round-trip efficiency of 57.35%, which is a 3.00 % advancement over the reference system. Beyond thermal efficiency gains, the proposed system demonstrates compelling environmental and economic advantages, including an annual carbon emission reduction of approximately 8.93 × 105 t, a net present value increase of 153.18 M$, and a shortened dynamic payback period by 2.06 years. Sensitivity analysis identifies an optimal recuperator inlet temperature of 50 °C and R245fa as the preferred working fluid. The study further reveals that enhancing isentropic efficiencies of compressors and turbines can progressively improve overall performance. These findings confirm the technical and economic viability of proposed system for large-scale energy storage.