Vanadium Redox Flow Battery (VRB) is an electrochemical energy storage system based on a reversible chemical reaction within a sealed electrolyte. Several models have been developed which now offer a good understanding of the VRB operating principles; this knowledge is important to evaluate its performance when applied in power systems. However, these models depend on parameters that are difficult to obtain experimentally or in data sheets. In this regard, this article presents a new VRB model based on the stack efficiency curves, usually determined by the manufacturer. This model is especially useful for computing intensive applications, such as power system dynamic studies, in order to maintain a low run-time. Finally, the simulation results obtained through the proposed model are compared with laboratory results of an experimental VRB system, showing a striking resemblance with only a little relative error arising from them. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.