A Novel Thermally Integrated CO₂-Carnot Battery (TI-PTES) Utilizing Cold Thermal Storage

The growing integration of renewable energy sources in the energy grid presents intermittency and negative pricing challenges, necessitating large-scale energy storage solutions. Pumped thermal energy storage (PTES) can address these issues by storing and delivering substantial energy whenever required. High-temperature heat pump development is crucial to deploying PTES for storing heat at sink temperatures that are well above the ambient temperature(>450 °C) to ensure a reasonable round-trip efficiency (RTE). Currently, however, it is not a technological possibility for heat pumps to achieve these temperatures even with the support of freely available heat (200 °C to 400 °C) as source temperatures. This study explores a potential layout of the TI-PTES system that exploits commercially available equipment by storing heat below the ambient temperature while still being able to utilize the freely available heat source (Solar, Waste heat, biomass, etc.) to support the overall RTE. The charging phase employs a well-established CO₂-refrigeration cycle to accumulate energy below the ambient temperature in cold thermal storage. While the discharging phase runs a trans-critical CO₂ power cycle between the freely available heat source and the cold thermal storage. Overall, offering a practically implementable model for the PTES system with market-available components. The study investigates the design of this innovative system presenting the relevance of different operating and machine parameters as well as the contribution of freely available heat sources to the overall performance. Finally, benchmarking the technology with other long-duration energy storages.