Performance Evaluation of sCO2–Hydrocarbon Mixtures in SBC-PTES Systems: A Parametric Thermo-Economic Study

The development of efficient and economically viable energy storage technologies is key to the integration of renewable energies. This study evaluates the thermo-economic performance of hydrocarbons as working fluids in PTES systems based on a simple Brayton cycle (SBC). Different hydrocarbon mixtures are analyzed to determine their impact on efficiency and costs, identifying optimal operating conditions and combinations that improve system performance and viability. The objective is to identify the optimal candidate and operating conditions for enhanced cost-effectiveness. A multivariable optimization was performed using a validated thermodynamic model, integrated with an economic evaluation framework. Key decision variables included pressure ratios, turbine inlet temperatures, and heat exchanger performance parameters, while several sCO2–hydrocarbon mixtures were evaluated as working fluids. Energy and exergy analyses were coupled with component-level cost correlations to determine round-trip efficiency, specific investment cost, and levelized cost of storage. The findings indicate that the CO2/C2H6 (60/40) mixture provides the best overall performance, achieving a round-trip efficiency of 54.38% and a levelized cost of storage of 137.1 $/MWh, outperforming pure CO2. Fluid selection exerts a substantial influence on both thermodynamic and economic indicators, with performance exhibiting a pronounced dependency on critical temperature, molecular complexity, and operating pressure levels. Sensitivity analyses indicate that improvements in heat exchanger effectiveness and turbomachinery efficiency yield substantial reductions in total system cost. The findings indicate that the appropriate alignment of hydrocarbon properties with system design parameters can significantly enhance the feasibility of PTES, offering a technically viable and economically competitive pathway for large-scale energy storage applications.