Exergoeconomic Analysis of a Gas Turbine Integrated with Supercritical CO2 Energy Storage and Cascade Heat Utilization Considering Different Operating Periods

With the increasing integration of renewable energy, large-scale energy storage systems are required to improve the flexibility of energy supply and alleviate the mismatch between power generation and demand. However, the performance evaluation of integrated energy systems combining continuous power generation and periodically operated energy storage remains challenging due to the different operating time scales of individual subsystems. In this study, a gas turbine integrated molten salt thermal energy storage and supercritical CO2 energy storage (GT-TES-CCES) system with cascade heat utilization is proposed. The proposed system recovers high-temperature exhaust heat from the gas turbine through molten salt storage, provides thermal input for CO2 expansion during discharge, and further utilizes residual heat for hot water production. A comprehensive thermodynamic and exergoeconomic model is developed, and a unified 24 h evaluation framework is introduced to consistently evaluate the continuously operated gas turbine subsystem and periodically operated charging/discharging processes. The SPECO method is employed to investigate the exergy cost formation and transfer characteristics, and multi-objective optimization is performed to identify the trade-off between exergy efficiency and product cost. At the nominal operating point, the proposed system achieves an electrical efficiency of 48.71%, an overall energy efficiency of 75.97%, and an exergy efficiency of 50.29%, with an instantaneous net power output of 40.26 MW during the discharge period and useful hot water production of 14.13 MW. After multi-objective optimization, the electrical efficiency and exergy efficiency increase to 53.99% and 54.82%, corresponding to improvements of 10.84% and 9.01%. Meanwhile, the total unit product exergy cost decreases from 14.32 to 13.55 $·GJ−1, demonstrating the economic benefit of the optimized configuration. The results indicate that the proposed multi-period exergoeconomic framework provides an effective approach for evaluating and optimizing integrated energy systems involving continuous power generation and flexible energy storage.