A new Redox flow battery system, vanadium-iron hybrid redox flow system, is developed. By using V2+/3+ redox couple containing solution in anolyte and using Fe2+/3+ and V4+/5+ containing solution as catholyte, this new system combines the advantages of both Fe-V and all vanadium systems, and eliminates their major disadvantages. Advantages with this new system over the previous systems have been demonstrated. To prevent Fe2+/3+ and V2+/3+ cations cross over through membrane, mixed Fe2+/3+ and V2+/3+ solutions is used for this new system.