Carnot battery with thermochemical energy storage and supercritical CO2 power cycle: Thermodynamic and techno-economic characteristics

The global transition toward decarbonized energy systems necessitates efficient long-duration energy storage solutions to address renewable intermittency. Conventional technologies face limitations in scalability, safety and geography, highlighting the promise of Carnot batteries. This study proposes a novel Carnot battery system integrating calcium hydroxide/calcium oxide thermochemical energy storage, supercritical CO2 Brayton heat pump and power cycles, and industrial waste heat recovery. Through multi-objective optimization using the NSGA-II algorithm and HEATSEP framework, the system achieved a round-trip efficiency of 67.95% and a LCOE of 1.200 RMB/kWh at 50 MW scale—placing it at a high level among current Carnot battery systems. Sensitivity analyses confirm robust scalability: when scaling from 10 MW to 50 MW, the LCOE decreases by 46.3% and the IRR increases from 6.79% to 13.64%. Furthermore, increasing the annual operating hours to 2560 h significantly reduces the LCOE while substantially raising the IRR. For high-cost materials, extending cycle life can yield 21.47% reduction in LCOE. Critically, system profitability is governed by discharge revenue. In markets with modest price differentials, economic feasibility therefore depends on additional reductions in capital cost, such as implementing deep integration with existing coal-fired assets. This integrated system and optimization directions provide a practical, generalizable blueprint for near-term, cost-competitive Carnot batteries.