It is worth mentioning that several optical sensors have already been developed for vanadium flow batteries, predominantly single-channel designs . These sensors typically detect colour changes using a photodiode and are valued for their low cost and high simplicity. However, their limited spectral information poses significant challenges. Specifically, they are unable to address calibration drifts due to variations of the total concentration C that are critical for maintaining long-term measurement robustness. These limitations are particularly pronounced in the posolyte due to its non-linear spectral response.