Coordinated Load and Flow Analysis for Enhanced System Efficiency in Vanadium Redox Flow Batteries: A System-Level Modelling Study

While vanadium redox flow batteries (VRFBs) are considered a promising technology for grid-scale energy storage, the combined influence of electrical load and electrolyte flow rate on overall system performance is often simplified in existing models. A MATLAB/Simulink-based system-level model of a 1 kW vanadium redox flow battery (VRFB) was developed to investigate the influence of load variation and electrolyte flow rate on battery performance. The model accounts for the flow-dependent behavior of key electrochemical parameters, including open-circuit voltage, internal resistance, and polarization losses. State of charge (SOC) is estimated using the Coulomb counting method, and a lumped first-order thermal model is included to represent stack temperature dynamics. The impact of auxiliary pump power is also considered to provide a realistic assessment of system efficiency. Results show that increasing the electrolyte flow rate from 5 LPM to 30 LPM reduces concentration polarization and improves voltage stability, leading to an increase in stack-level electrical efficiency from approximately 85% to more than 92.5%. However, the improvement in overall system efficiency becomes less pronounced at higher flow rates because of the nonlinear increase in pump power consumption.Thermal analysis indicates that stack temperature rise is mainly influenced by electrical loading, whereas higher electrolyte flow contributes to enhanced heat removal and produces only a slight reduction in overall stack temperature. The study highlights the importance of considering both electrochemical performance and auxiliary energy consumption when evaluating VRFB systems and provides useful insights into the coordinated operation of load and electrolyte flow conditions.