A Novel Thermally Integrated CO2-Carnot Battery Utilizing Cold Thermal Storage

Abstract The growing integration of renewable energy sources in the energy grid presents challenges related to intermittency and negative pricing, necessitating large-scale energy storage solutions. Pumped Thermal Energy Storage (PTES) is an innovative system designed to address these issues by storing and delivering substantial energy in the form of heat using thermal heat pump and power cycles respectively. High temperature heat pump development is crucial to the deployment of PTES as it needs to store heat at 450°C above the ambient temperature to ensure a reasonable round trip efficiency (RTE). Currently however, it is not a technological possibility for heat pump machinery to achieve these temperatures even with integration of freely available heat sources (200°C to 400°C) which can support the heat pump cycle from a RTE standpoint. This study explores a potential layout of TI-PTES system that exploits commercially available equipment by storing heat below the ambient temperature while still being able utilize the freely available heat source (Solar, Waste heat, biomass etc.) to support the overall RTE, in the power cycle instead. The charging phase employs a well-established CO2-refrigeration cycle to accumulate energy below the ambient temperature in a 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 design of this innovative system presenting the relevance of different operating and machine parameters as well as the contribution of freely available heat source in the overall performance. Finally benchmarking the technology with other long duration energy storages.