Techno‐Economic Analysis of Hydrocarbon‐CO 2 Binary Mixtures in Heat Pump‐Based Thermal Energy Storages

The transition to renewable energy increases the demand for efficient energy storage technologies, such as Carnot batteries (CB), to balance supply and demand. This study investigates the heat pump charging of the thermal storage for a CB starting at ambient temperature and operating with CO 2 ‐containing fluid mixtures. Thermodynamic optimization of operating conditions is performed within the pressure range of commercially available compressors and hot storage temperatures of 363.15–398.15 K. Butane–CO 2 and isobutane–CO 2 mixtures containing 15%–20% CO 2 achieve an optimal coefficient of performance of approximately 4.1, corresponding to a 70 K hot‐storage temperature lift. Pentane–CO 2 and isopentane–CO 2 mixtures reach 398.15 K but operate with lower efficiency. Exergy analysis shows that while mixtures reduce heat‐exchanger irreversibility, throttling losses increase with higher CO 2 content, with relative exergy destruction in the expansion valve reaching ∼55% at 40% CO 2 . Although increasing CO 2 mitigates flammability, it penalizes performance and raises system costs. Economic evaluation indicates that butane–CO 2 and isobutane–CO 2 mixtures require specific investment costs (SIC) of 1150–1350 $ kW −1 and a levelized cost of heat (LCOH) of 0.156–0.177 $ kWh −1 at 900 operating hours per year. Both SIC and LCOH are more sensitive to mixture composition than to storage temperature.