Techno-economic evaluation of a Rankine Carnot battery coupling air-source energy and salt hydrate thermochemical heat transformer

The urgent need for geographically flexible, large-scale, and long-duration energy storage solutions to support renewable energy integration highlights critical limitations in conventional thermal storage systems. To achieve high energy density and heat quality upgrading, this article introduces a novel air-source energy-driven Rankine-Carnot battery system employing cascaded salt hydrate-TCES modules to enhance energy density, round-trip efficiency, and economic viability. Comprehensive modeling and techno-economic evaluations are performed for the systems based on two storage configurations: pressurization-assisted thermochemical energy storage and pressurization-assisted cascade thermochemical energy storage with condensation heat recovery. Results reveal that the latter possesses a better thermodynamic performance, yielding a significant round-trip efficiency of 67.73 %, an exergy efficiency of 71.89 %, and a heat storage density of 136.38 kWh/m³. Furthermore, the system demonstrates a competitive levelized cost of storage of 0.214 $/kWh. In both proposed Carnot batteries, heat pump condensers cause the greatest exergy destructions of 1734.24 kW and 1005.19 kW, occupying 27.7 % and 29.6 % of the total; the compressor and expander are the most expensive components, the sum of which accounts for over 50 % of the total investment. Additionally, the cost of storage modules and thermochemical materials occupy noticeable ratios in the two systems. Parametric analyses highlight the impact of storage temperature, discharging temperature, ambient temperature, isentropic efficiencies of the compressor and expander, daily charging time, and pinch point temperature difference on system performance. Notably, the pressurization-assisted cascade thermochemical storage with condensation heat recovery module-based Carnot battery maintains a superior levelized cost of storage across diverse operating conditions, making it a promising candidate for a geographically independent and economically viable energy storage strategy.