Storage systems are becoming one of the most critical components in the scenario of energy, mainly due to the penetration and deployment of renewable sources. All-vanadium redox-flow batteries (RFB), in combination with a wide range of renewable energy sources, are one of the most promising technologies as an electrochemical energy storage system because of the independence of energy and power rating, fast response, room temperature operation, extremely long life, and low environmental impact. This article reviews the main features and applications of vanadium as a key element of RFB and provides a simple explanation of its properties and use as a means of energy storage.