A Field Validated Modeling and Estimation of Capacity Fade and Its Recovery for Vanadium Redox Flow Battery

This paper presents the modelling and estimation of capacity fade in vanadium redox flow battery (VRFB) storage with an objective to study its impact on the field performance of a kW-scale VRFB system. The dynamic behavior of electrolyte volume and reactant concentrations has been considered in estimating VRFB capacity fading model, in MATLAB/Simulink environment. The proposed model demonstrates that electrolyte rebalancing can improve VRFB capacity recovery by up to 36%. Over 1000 charge/discharge cycles, VRFB capacity fade has been reduced from 81.8% to 45.8% which is a significant improvement. The long-term estimations using the proposed model indicate a viable VRFB cycle life of 16,000 cycles, with a capacity fade of 83.42% after 20,000 cycles. A practical case study on a solar-VRFB microgrid indicates that systematic electrolyte rebalancing of VRFB can significantly satisfy peak load delivery over a long period of around 10000 cycle life. The proposed capacity fade model and recovery strategy for VRFB is a generalized solution and suitable for long-term analysis in large-scale VRFB storage deployments.