Energy transition requires a high penetration of reliable and flexible renewable energy. To do so, low-cost, efficient, high capacity and environmentally friendly storage technologies to manage the mismatch between energy production and demand are required. Carnot Batteries are considered as promising energy storage solutions tackling these requirements and storing electrical energy as thermal energy and releasing it whenever necessary while operating on reversible thermodynamic cycles. In Carnot Batteries, power is managed through rotating machines, such as compressors and turbines, and energy is stored as heat in thermal energy storages. In recent years, thermal cycles exploiting Carbon Dioxide (CO2) as operating fluid, in sub-critical, trans-critical and supercritical conditions, are gaining major interest, thanks to their versatility and high performance, especially for large scale applications. This paper provides an in-depth review on the state of the art of global R&D activities on the use of carbon dioxide for large scale Carnot Battery application, while providing preliminary market and technology maturity breakdown. Different studies on CO2-Carnot Batteries at industrial and academic levels are discussed in detail while highlighting the novelty and improvement methods. Detailed information on battery parameters of charging, discharging and storage have been listed and critically analysed, finally concluding with SWOT (Strength, Weakness, Opportunity, Threats) and TRL (Technology Readiness Level) analyses for future developments.
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