Thermo-Economic Optimization of an Electric-Heater-Assisted Reversible HP–ORC Carnot Battery System Considering Charging Mode and Working Fluid Selection

Carnot batteries are promising sustainable energy storage technologies for renewable electricity utilization and grid peak shaving. For broader applicability and flexible configurations, an electric-heater-assisted reversible heat pump–organic Rankine cycle Carnot battery was investigated under two charging modes using six working fluids. A thermo-economic model was developed, comprising segmented ε-NTU heat exchangers, a pressure-ratio off-design, and levelized cost of storage. Latin hypercube sampling, Gaussian process regression, global sensitivity analysis, NSGA-II, and entropy-weight TOPSIS were used for variable identification, Pareto optimization, and decision-making. The rated pressure ratio dominates round-trip efficiency under the electric-heater-first mode, whereas the evaporation temperature of the organic Rankine cycle dominates both objectives under the heat-pump-first mode. The heat-pump-first mode achieves higher round-trip efficiency and a lower levelized cost of storage for six working fluids. The R1234yf-electric-heater-first configuration is usually suitable for applications prioritizing high-temperature heat supply. However, considering environmental friendliness and sustainability, R1233zd(E)-heat-pump-first is recommended for the system, achieving 15.709% and 0.36562 $/kWh, respectively. Admittedly, the potential transient-response advantage was not quantified by the present steady-state model, which can be further investigated in the future.