anadium redox flow battery (VRFB) systems complemented with dedicated power electronic interfaces are a promising technology for storing energy in smart-grid applications in which the intermittent power produced by renewable sources must face the dynamics of requests and economical parameters. In this article, we review the vanadium-based technology for redox flow batteries (RFBs) and highlight its strengths and weaknesses, outlining the research that aims to make it a commercial success. Present electric energy production exceeds 10 3 and is growing at a rate of about 3% per year [1]-[3]. For approximately four decades, scientific forecasts warned that conventional resources could not stand this increasing demand in the long term [4], [5], and, only recently, the central administrations of all industrialized countries have embedded into their development programs several policies to gradually replace carbon-based plants with environmentally friendly renewable sources. Following these programs, world wind-generating capacity