Exergetic-cost analysis of pumped thermal energy storage (PTES) systems using s-CO2 mixtures as a working fluid

This study provides a comprehensive exergy-cost analysis of pumped thermal energy storage (PTES) systems utilizing supercritical CO 2 (s-CO 2 ) mixtures. It specifically examines CO 2 /Kr and CO 2 /Xe as working fluids, comparing their performance to that of pure s-CO 2 . PTES technology, based on the Brayton cycle, efficiently stores electrical energy as thermal energy, which can later be reconverted into electricity. System optimization is achieved through the use of multi-objective genetic algorithms, such as the Non-dominated Sorting Genetic Algorithm II (NSGA-II), which balances thermodynamic performance with economic feasibility. By fine-tuning key parameters, such as compressor and turbine inlet pressures and efficiencies, this study investigates the relationship between round-trip efficiency and the levelized cost of storage (LCOS). The results indicate that s-CO 2 mixtures outperform pure s-CO 2 by achieving higher round-trip efficiency and lower LCOS values. The findings of this study show that the CO 2 /Xe mixture, with a molar fraction of 0.80/0.20, delivers the best performance, achieving an LCOS of 104.25 $/MWh and a round-trip efficiency of 66 % for a net power of 100 MW. This mixture demonstrates a significant advantage over pure s-CO 2 , which under similar conditions results in an LCOS of 116.44 $/MWh. These results highlight the potential of such systems to facilitate the integration of renewable energy. Further advancements are expected through the exploration of alternative working fluid mixtures and system topologies.