Innovative design and behavior investigation of the Carnot battery energy storage system: A pathway towards efficient utilization of renewable energy

To address the electricity supply–demand imbalance caused by the inherent volatility and intermittency of renewable energy sources, a supercritical Brayton cycle is coupled with a CO₂ heat pump for energy storage and power generation. This configuration represents an innovative exploration of Carnot battery technology. An in-depth study on working fluid selection and parameter optimization to maximize the energy utilization efficiency and minimize the investment cost for the combined system was conducted. The results indicate that the CO₂-Xe/CO₂ system outperforms the CO₂-Kr/CO₂ and CO₂/CO₂ systems, achieving a round-trip efficiency of 65.8 % and a payback period of 9.23 years under design conditions. The system also demonstrates an improvement in round-trip efficiency and a reduction in investment cost when compared to the energy storage systems documented in the existing literature. System performance declines under off-design conditions but can be enhanced by adjusting operating parameters. The system demonstrates effective operation within partial load (80 %-100 %) and partial input power (80 %-105 %) ranges, with round-trip efficiency experiencing minor variations between 65.8 %-62.85 % and 65.8 %-63.87 %, respectively. The findings indicate the feasibility of the proposed combined energy storage and power generation system.