Vanadium redox flow batteries: A technology review

By Jorge Martins and Francisco P. Brito for University of Minho

Flow batteries have unique characteristics which make them especially attractive when compared with conventional batteries, such as their ability to decouple rated maximum power from rated energy capacity, as well as their greater design flexibility.
The vanadium redox flow batteries (VRFB) seem to have several advantages among the existing types of flow batteries as they use the same material (in liquid form) in both half-cells, eliminating the risk of cross contamination and resulting in electrolytes with a potentially unlimited life. Given their low energy density (when compared with conventional batteries), VRFB are especially suited for large stationary energy storage, situations where volume and weight are not limiting factors. This includes applications such as electrical peak shaving, load leveling, UPS, and in conjunction with renewable energies (e.g. wind and solar).

The present work thoroughly reviews the VRFB technology detailing their genesis, the basic operation of the various existing designs and the current and future prospects of their application. The main original contribution of the work was the addressing of a still missing in-depth review and comparison of existing, but dispersed, peer reviewed publications on this technology, with several original and insightful comparison tables, as well as an economic analysis of an application for storing excess energy of a wind farm and sell it during peak demand. The authors have also benefited from their background in electric mobility to carry out original and insightful discussions on the present and future prospects of flow batteries in mobile (e.g. vehicle) and stationary (e.g. fast charging stations) applications related to this field, including a case study.

VRFBs are currently not suitable for most mobile applications, but they are among the technologies which may enable, when mature, the mass adoption of intermittent renewable energy sources which still struggle with stability of supply and lack of flexibility issues.

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