Carnot Battery with open-cycle ultra-high-temperature heat pump for large-scale hybrid PV and concentrating solar power plants

Serious curtailment issues in large-scale renewable energy plants which are often located in remote and harsh environments, create an urgent demand for safer, more efficient and flexible energy storage solutions. This study proposes a novel Carnot Battery system based on an open-cycle ultra-high-temperature heat pump and a tower concentrating solar power (CSP) configuration. The open-cycle air-based heat pump is integrated into CSP plant which is already equipped with molten salt thermal storage and sCO2 power block, serving to recover residual heat during discharging and enhance overall energy utilization. Thermodynamic models for charging/discharging cycles and solar plants were established for a system with 10 MW power output. Sensitivity analysis on the component performance was conducted and the influence of operation conditions on performance was also investigated. Results show that the proposed system achieves a round-trip efficiency of 56.2 % under typical operating conditions, with a potential increase to 62.5 % at lower discharging pressure ratio. In addition, the operational characteristics of the proposed system were evaluated on typical seasonal days, revealing a peak COP of 1.42 in summer. For the 10 MW system, coupling with a 60 MW photovoltaic (PV) capacity was found to be optimal, reducing average fluctuation magnitude of PV by 25–34 %. Moreover, the system can reduce the required heliostat filed area by 28.5 % or increase the power output by approximately 20 % compared with conventional PV-CSP hybrid plant. It offers a promising solution to store surplus electricity and convert it into dispatchable power efficiently in hybrid PV-CSP plants.