Thermodynamic and techno-economic analysis of a novel solar-driven liquid CO₂ energy storage system

Efficient and flexible energy storage technologies are essential to accommodate the growing share of renewable energy in power systems. To address the limitations of conventional storage systems in terms of energy density and structural complexity, this study proposes a novel liquid carbon dioxide energy storage system that integrates self-evaporation and ejector-assisted condensation. Three configurations, including the basic system, the solar-assisted system, and the system integrated with an Organic Rankine Cycle (ORC), are comparatively analyzed to evaluate their thermodynamic and economic performance. The results indicate that the ORC integrated system achieves the best overall performance, with a round-trip efficiency of 105.61%, an exergy efficiency of 68.13%, a solar energy conversion efficiency of 22.33%, and the lowest levelized cost of electricity of 0.23 $/kWh. Parametric analyses reveal that optimizing inlet pressure enhances vapor generation during self-evaporation, while ejector performance depends strongly on primary flow rate, back pressure, and low-pressure tank conditions. Increasing the operating pressure and solar collector temperature further improves system efficiency and cost-effectiveness. Overall, the proposed system demonstrates strong potential for achieving high-efficiency and economically viable large-scale energy storage through the synergistic utilization of solar and waste heat resources.