Application of zeotropic mixtures in Carnot batteries: Energy, exergy, economic and environmental (4E) analysis

The Carnot battery, an emerging large-scale energy storage technology, has garnered significant attention due to its high compatibility with renewable energy and waste heat source. At present, although there are many studies on Carnot batteries, there are still few studies on the application of zeotropic mixtures in Carnot batteries. Consequently, this study selects three types of Carnot batteries and constructs their models utilizing Aspen HYSYS. The genetic algorithm within MATLAB is used to optimize the performance of the system. The energy, exergy, economic and environmental performance of the system are analyzed to compare the performance gap between pure fluids and zeotropic mixtures in the system. The findings indicate that the PR-PTES system demonstrates superior performance, achieving a maximum round trip efficiency (η_rt) of 84% when the thermal storage temperature is maintained between 85 and 95 °C. The maximum increase of η_rt, energy storage density (ESD) and air emission reduction (AER) are 37.9%, 18.2% and 17.1%, respectively, when the PR-PTES system uses zeotropic mixtures compared with pure fluids. This enhancement is attributed to the temperature glide of the zeotropic mixtures, which facilitates improved temperature matching between the hot and cold fluids within the heat exchanger, consequently boosting the system's performance. Furthermore, the research reveals that the HP subsystem, when employing R1233zd(E)/R290 as the working fluid, exhibits optimal performance. Meanwhile, the ORC subsystem achieves its best performance with R1233zd(E)/R1234ze(E) as the working fluid. © 2026 Elsevier Ltd.