Multi-objective optimization and design of a Carnot Battery for energy storage applications

• Multi-objective optimization framework for Carnot Batteries design is proposed. • Six configurations and sixteen combinations of working fluids were tested. • Operational parameters optimized using TOPSIS method and TRADeS decision tool. • Both Heat pump and ORC with regenerators and R1233zd(E) achieve the best results. • A system RTE of 81.30 % and LCOS of 1.09 €/kWh is obtained for the design condition. This study presents a numerical design and optimization of a Heat Pump-Organic Rankine Cycle based Carnot Battery, focusing on determining the optimal nominal operating conditions for selecting key components for the construction of a small-scale test rig. Initially, the mathematical models of the six Carnot batteries are established and validated by published literature data. Afterwards, the optimization procedure is divided into a single-objective optimization and a multi-objective optimization, focusing on balancing three key performance parameters of the system: energetic, exergetic and economic. In the single-objective optimization, six distinct system configurations and sixteen combinations of four environmentally friendly working fluids were subjected to analysis. A score was assigned to each combination of working fluids and system configurations. The set with the highest score undergoes multi-objective optimization to obtain a Pareto front and determine the optimal operating condition. The use of regenerators in both heat pump and organic Rankine cycle with R1233zd(E)-R1233zd(E) as the working fluid combination achieves the optimal balance between thermodynamic and economic performance. The combinations using R1234ze(Z) in the HP cycle also yielded excellent results in all systems. The design condition of the lab-scale system achieves a roundtrip efficiency of 81.30 % and LCOS of 1.09 €/kWh.