Thermodynamic and exergoeconomic analysis and multi-objective optimization of a novel tank-free transcritical CO₂ energy storage system

A novel Tank-Free Transcritical CO₂ Energy Storage System (TF-TCCES) is proposed and analyzed from thermodynamic and exergoeconomic perspectives. Unlike traditional Compressed Gas Energy System (CGES) relying on high-pressure vessels, the proposed configuration eliminates external tanks by coupling heat storage, cold storage and discharging cycles, thereby avoiding the associated high costs and safety risks. A steady-state model was established using the SPECO method. Baseline results show a round-trip efficiency (RTE) of system is 40.89 %, the exergy round-trip efficiency (ERTE) of the system is 41.36 % and the overall cost per unit of energy produced (c_ptot) of system is 14.87 $/GJ, demonstrating competitive economic potential compared with conventional systems. Exergy analysis shows that turbine T3, compressor C2, the cooler and the heater are the main sources of irreversibility, while exergoeconomic analysis identifies the pump and turbines T1 and T3 as the main cost drivers. Sensitivity analyses show that cycle maximum pressures and compressor efficiency have the greatest impact on the system performance. A multi-objective optimization was applied to maximize ERTE and minimize c_ptot at the same time. The Pareto front demonstrates a clear trade-off between thermodynamic and economic performance, with ERTE ranging from 30 % to 55 % and c_ptot from 13.2 to 30.0 $/GJ. The optimized ERTE is 50.10 %, RTE is 49.21 % and c_ptot is 16.85 $/GJ, offering a balanced design with competitive efficiency and economic feasibility. The results show that the proposed tank-free system provides an efficient, compact, and economic alternative for large-scale energy storage.