Low-cost optical multi-wavelength sensor for accurate real-time state-of-charge monitoring in vanadium flow batteries

We present a novel, low-cost optical sensor for accurate real-time monitoring of the state of charge (SoC) and total vanadium concentration in vanadium flow batteries. Using only six discrete wavelengths, the sensor achieves precision comparable to full-spectrum methods while significantly reducing equipment costs and complexity. A general deconvolution method is used to measure the SoC and the total vanadium concentration in both the negolyte and posolyte, with calibration covering concentrations from 1.21 to 1.82 mol/L. We achieve root mean square error (RMSE) values of 1.2% and 3.2% for the SoC, and 54 mmol/L and 97 mmol/L for the total vanadium concentration in the negolyte and posolyte, respectively, demonstrating excellent agreement with reference ultraviolet visible (UV-vis) data. In addition, a wavelength optimization study is proposed to determine the optimal number and placement of spectral channels, providing a basis for the design of tailored optical sensors for vanadium electrolytes.