Vanadium redox flow batteries (VRFBs) have power rating and energy durations that are independent of one another, which make them attractive for power systems applications. This paper focuses on the energy and power response capability of the VRFBs, which has been experimentally researched based on 5 kW/10 kWh and 0.5 MW/1 MWh systems. With three experimental operating modes, three threshold values and one baseline have been obtained based on the experimental results. The maximum state of charge ("SOC"), charged by 1.4 times rated power at I time ratio ("TR"), is 47% SOC. The minimum TR, charged by times rated power at SOC = 100%, is 1.5. The maximum charge/discharge power rating is 1.35 times rated power. The reserve SOC curves are a baseline on which the VRFB can respond to equally charge/discharge energy demand. (C) 2013 Elsevier B.V. All rights reserved.