The paper "Carbon dioxide energy storage systems: Current researches and perspectives" by Florent Dewevre, Clément Lacroix, Khaled Loubat, and Sébastien Poncet reviews the current state and future prospects of Carbon Dioxide Energy Storage (CCES) systems. CCES, similar to Compressed Air Energy Storage (CAES), uses CO₂ as the working fluid but operates under non-extreme temperature conditions, allowing for liquid storage. The authors classify CCES systems based on external heat use and storage location (underground or aboveground) and discuss their thermodynamic, economic, and experimental aspects. Key points include: - **Thermodynamic Performance**: CCES systems can achieve high exergy efficiencies (60-70%) and energy densities (up to 36 kWh/m³). Systems with low-pressure storage at ambient temperature or gaseous storage at low pressure generally have higher efficiency and energy density. - **Economic Analysis**: The Levelized Cost of Storage (LCOS) is a critical factor, influenced by capital expenditures, operational costs, and external heat costs. Hybrid systems, such as CCES combined with renewable energy sources, show potential for cost-effectiveness. - **Experimental Studies**: Limited experimental studies have been conducted, primarily focusing on subcritical cycles with gaseous CO₂ storage. The development of high-pressure CO₂ components is crucial for further advancements. - **Future Research**: The paper highlights the need for more dynamic models, experimental validation, and research on turbomachinery and thermal storage components to improve the performance and reliability of CCES systems. Overall, the paper provides a comprehensive overview of CCES, emphasizing its potential as a large-scale, cost-effective, and environmentally friendly energy storage solution.The paper "Carbon dioxide energy storage systems: Current researches and perspectives" by Florent Dewevre, Clément Lacroix, Khaled Loubat, and Sébastien Poncet reviews the current state and future prospects of Carbon Dioxide Energy Storage (CCES) systems. CCES, similar to Compressed Air Energy Storage (CAES), uses CO₂ as the working fluid but operates under non-extreme temperature conditions, allowing for liquid storage. The authors classify CCES systems based on external heat use and storage location (underground or aboveground) and discuss their thermodynamic, economic, and experimental aspects. Key points include: - **Thermodynamic Performance**: CCES systems can achieve high exergy efficiencies (60-70%) and energy densities (up to 36 kWh/m³). Systems with low-pressure storage at ambient temperature or gaseous storage at low pressure generally have higher efficiency and energy density. - **Economic Analysis**: The Levelized Cost of Storage (LCOS) is a critical factor, influenced by capital expenditures, operational costs, and external heat costs. Hybrid systems, such as CCES combined with renewable energy sources, show potential for cost-effectiveness. - **Experimental Studies**: Limited experimental studies have been conducted, primarily focusing on subcritical cycles with gaseous CO₂ storage. The development of high-pressure CO₂ components is crucial for further advancements. - **Future Research**: The paper highlights the need for more dynamic models, experimental validation, and research on turbomachinery and thermal storage components to improve the performance and reliability of CCES systems. Overall, the paper provides a comprehensive overview of CCES, emphasizing its potential as a large-scale, cost-effective, and environmentally friendly energy storage solution.