With a rapid charge/discharge feature, vanadium redox flow batteries (VRBs) are green, large-scale energy storage devices useful for power smoothing in unstable renewable power generation facilities, such as those involving solar and wind energy. This study developed a VRB model to establish a relationship between electrolyte concentration, equilibrium potential, and state of charge (SOC), to simulate the dynamic responses in charge/discharge cycles of the electrolyte concentration, terminal voltage, and SOC, and to evaluate the internal loss and battery efficiency. The proposed model not only serves as the basis of a dynamic analysis tool for future studies for designing a large-scale VRB but also reveals the time-varying electrolyte status for a long-term VRB operation.