Multi-objective exergy-based optimization of a Carnot battery under different charging/discharging durations

This study aims to apply an exergy, economic, and exergoeconomic analysis, as well as a multi-objective optimization, of a Carnot battery energy storage system consisting of an organic Rankine cycle and a vapor-compression heat pump. The innovation of research is evaluating the effect of the charging and discharging durations on the characteristics of the Carnot battery. The following charging/discharging durations are included in the multi-objective optimization: 6/6 (the so-called balanced option, commonly applied in many studies and used to validate the model), 8/4 and 12/6 (double), and 12/4 (triple). It is found that the charging/discharging time rates play a significant role in the thermodynamic and economic characteristics of a Carnot battery. The highest value of the round-trip efficiency, 42.2% (exergetic efficiency of 22.5%), was obtained for the 6/6 optimal case, while the cost of the discharged electricity, $ 219.54/GJ, is the highest. The lowest cost of electricity is observed for the 12/4 optimal case (89.29 $/GJ, i.e., 40% of the 6/6 optimal case). However, the round-trip efficiency is 39.2% (a 7% drop), and the exergetic efficiency is 11.5% (a nearly 50% drop). The optimization results indicate that it is feasible to achieve improvements in thermodynamic and economic performances through parametric optimization; for example, the highest exergetic performance of the system and the lowest costs of the generated electricity are observed for the temperature at the inlet of the turbine at around 100 ° C for all charging/discharging durations under the considered operation conditions. • State of the art of exergy-based evaluations of Carnot batteries is discussed • Sensitivity analysis for the Carnot batteries under different operation conditions is reported • Multi-criteria optimization of the Carnot batteries under different operations conditions is conducted • The influence of charging/discharging durations on results is highlighted