Analysis of Performance and Multi-Objective Optimization of a Carnot Battery Utilizing Ship Waste Heat

Abstract During berthing, ships rely on auxiliary diesel engines for power, leading to suboptimal fuel efficiency and significant carbon emissions that compromise port air quality and public health. This article proposes a Carnot battery system designed for dual utilization of ship waste heat, which collects and stores waste heat from the main engine during navigation, converts it to electricity to supply power while docked, and thereby reduces emissions while improving energy efficiency. Four models were developed for the system. Single-objective optimization was performed on five working fluids to identify the optimal one. Nondominated sorting genetic algorithm II (NSGA-II) was used to perform a multi-objective optimization targeting levelized cost of storage (LCOS) and round-trip efficiency. The optimal solution under specified operating conditions was determined via multicriteria decision-making (MCDM), accompanied by a comparative analysis of component costs and exergy characteristics. The results indicate that R1234ze(Z) is the optimal working fluid, yielding a maximum round-trip efficiency of 42.52%. The optimization further reveals that different design criteria should be applied to the compressor and expander to reconcile thermodynamic performance with economic considerations. Under the optimal solution, heat exchangers dominate exergy destruction (68.42%), while the expander and compressor constitute the highest investment costs, accounting for 41.27% and 16.27% of the total investment, respectively.