Technical benchmarking and challenges of kilowatt scale vanadium redox flow battery

Unique features of vanadium redox flow battery (VRFB), such as easy scalability and long durability, qualifies it as one of the prominent renewable energy storage technologies. Attracted by its features, scientific and commercial community around the globe have now begun to test prototypes/demonstrations of VRFB for a wide array of applications that deal at a scale of kW‐MW. A few scientific groups have discussed the design and performance of kW‐scale (up to 10 kW) VRFB in literature. It is interesting to note that the discussed designs have been developed with a diverse approach and have achieved different results. In this review, we critically examine and discuss those contributions at kW‐scale VRFB by analyzing the materials associated with their design, understanding the development of the flow engineering aspects in order to tackle the pressure and shunt current losses and the overall electrochemical performance. Till date, kW‐scale VRFB system has achieved an energy efficiency of ~80% at current densities of 100 mA⋅cm−2. Though the choice for majority of VRFB components is fixed, the right choice for its separator/membrane still needs to be standardized. With these aspects in picture, this review article will help to lay a background for researchers and engineers to know the present state‐of‐art and engineering issues at kW‐scale VRFB, which is a building block for scaling up.