Thermo-economic performance analysis of two novel isobaric liquid carbon dioxide energy storage systems coupled with pumped hydro storage

Liquid carbon dioxide energy storage is a promising technology for stabilizing renewable power output; however, the inefficiency and diseconomy caused by non-isobaric storage are generally overlooked. In response, this study proposes two novel isobaric liquid carbon dioxide energy storage systems coupled with pumped hydro storage, the pumped hydro storage-assisted and high backpressure pumped hydro storage-assisted systems. These systems achieve isobaric storage by incorporating hydraulically designed carbon dioxide-water co-storage tanks. The study begins with a dynamic behavior analysis of the basic system, followed by a thermo-economic performance comparison, parametric analysis, and an economic uncertainty analysis based on multi-objective optimization. Results show that neglecting non-isobaric storage in the basic system leads to a 26.44 % discrepancy in total exergy efficiency, a 59.67 % relative deviation in energy storage density and an economic overestimation. By avoiding unsteady-state operation, the high backpressure pumped hydro storage-assisted system outperforms the other two, achieving a total exergy efficiency, levelized cost of storage and net present value of 52.95 %, 0.131 $/kWh and 32.24 M$, respectively, while the pumped hydro storage-assisted system achieves the highest energy storage density at 3.85 kWh/m³. To further enhance thermo-economic performance, attention can be paid to key components such as compressor, turbine, condenser and tanks. Additionally, the high backpressure pumped hydro storage-assisted system exhibits the most favorable and stable economic performance, with a levelized cost of storage of 0.154 ± 0.022 $/kWh and a net present value of 22.11 ± 9.05 M$. The system economic viability can be further improved by expanding discharge capacity and operating durations, particularly in regions with favorable electricity price structures.