Monitoring of Vanadium Redox Flow Battery State-of-Charge using Color Analysis

Ensuring power grid stability in the face of intermittent renewable sources, such as solar and wind, necessitates the deployment of effective energy storage solutions. Among the available technologies, Vanadium Redox Flow Batteries (VRFBs) stand out, offering a compelling combination of scalability, inherent safety, and extended operational lifespan. However, unlocking the full potential of VRFBs is often hindered by the challenge of precise State-of-Charge (SoC) monitoring. Conventional techniques, namely Coulomb counting and open-circuit voltage (OCV) measurements, frequently fall short in terms of accuracy. To address this limitation, this work details a color-based method utilizing an RGB sensor coupled with a flow-through cuvette for real-time SoC assessment. The method's calibration was performed with 1.6 M electrolytes of known ionic compositions, followed by validation during charge-discharge cycling on a lab-scale VRFB. The results demonstrate a robust correlation between the measured RGB values and the battery's SoC, achieving an average Root-Mean-Square (RMS) error below 3% and a maximum deviation of less than 5 % when benchmarked against OCV-based estimations. Consequently, this non-invasive technique offers a reliable and cost-effective alternative to conventional monitoring methods.