Abstract: State of charge (SOC) indicates the ratio of the schedulable capacity to that of available maximum W·h capacity in an energy storage system, which is necessary parameter for energy storage applications. This study clarified SOC concept framework for all vanadium redox flow battery from both theory and applications, proposed two approaches to determine the maximum W·h capacity. The measured method has high accuracy, containing information relative to vanadium ions transport and water diffusion through membranes, hydrogen emission and oxidization in the negative electrolyte by side-reaction, having promising potential for use in the characterization of the state of charge in practical system. We also elaborated the relationship of the maximum W·h capacity, electrochemical W·h capacity and theoretical W·h capacity. It can be expected that this method can be used to determine the state of charge in vanadium redox flow battery R&D process.

Key words: flow battery, state of charge, maximum W·h capacity, measurement