Vanadium Redox Flow Battery (VRFB) For Solar Storage

Categories: Solar Battery Storage.

Vanadium Redox Flow Battery (VRFB) In Context

The Vanadium Redox Flow Battery is a type of rechargeable battery for solar storage.


Vanadium Redox Flow Battery technology is moving towards residential applications so read on about how good it works commercially.


In 2017, the weighted average electricity costs from renewables (bioenergy for power, hydropower, geothermal, wind and solar PV) all fell within the range of fossil fuel-fired electricity and competed head-to-head with fossil-fuels without financial support. (IRENA).


Renewables were often the cheapest source of new generation production. Solar PV module costs have fallen by about four-fifths in ten years, making residential solar PV systems around two-thirds cheaper than in 2010.


For the integration of the more variable renewable sources, such as solar and wind energy into the power grid, better energy storage capabilities within the grid are going to become crucial. VRFB technology works effectively for grid scale power storage.


Battery storage technologies for distributed renewable energy outputs are already cost-competitive for remote island and mining applications. The market for battery storage systems linked with rooftop solar panels is ready for growing rapidly.

Vanadium Redox Flow Battery

What Is A Vanadium Redox Flow Battery (VRFB)?

Redox stands for "reduction and oxidation" meaning the chemical process of these batteries. An oxidation-reduction reaction is a chemical reaction where the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron.  The battery uses vanadium ions in several oxidation conditions for storing potential energy.


The battery stores direct current from solar PV collectors. This use exploits the capability of vanadium ions to exist in solution in four (4) oxidation states. An amazing feature of this flow battery is that it's made as an electrical storage device with a single electroactive liquid component. Currently vanadium batteries are bulky, so are massive in size. Most vanadium redox flow battery sets are used for energy storage solutions at large scale solar power stations.


The sun is an abundant source of free power. Everyone has access to its unlimited solar energy. Energy is available to capture when there is sunlight and the large solar generation schemes need large storage regimes to hold the captured energy. There is work being done to improve solar batteries within the VRFB arena.


The Vanadium Redox Flow Battery initiated in the early 1930s by Pisoort. Pellegri, Speziante and NASA developed it during the mid 1970s, but none of them emerged with a proven commercial technology. The first successful demonstration of the vanadium redox flow battery for solar storage was in the early 1980s. That demonstration was by Maria Skyllas-Kazacos at the University of South Wales, Australia.

How Does A Vanadium Redox Flow Battery Work

VRFB technologies have showcased their capability to supplement large scale solar energy storage. VRFB get used for applications like the remote area power supply (RAPS). They work for back-up power storage, power quality optimization and distributed power generation.


Most of these applications get measured at the kilowatt power measurement range. They also apply for Megawatt and Gigawatt size storage measurements. VRFB give the possibility to contribute to:

  • Enhanced energy flexibility and efficiency of the national electricity grids.
  • Saving solar power into its storage to help peak load levelling.
  • Grid stabilization of power obtained from renewable energy based sources.

The basics of load leveling is the use of solar energy storage instead of using coal base generation. The conventional combustion or thermal based spinning reserve is still available. This large storage method enhances the capability of renewables in times of high generation and low demand. It lessens the need for peaking power turbines using natural gas.


An often quoted downside of renewables is grid instability when contribution levels reach 30 percent. This is because photovoltaic and wind power sources contribute an irregular energy flow supply. Energy from the environment like solar energy is not laminar. Using VRFB technology provides solar energy grid stability in geographically limited areas. The VRFB serves as a permanent backup during intermittent weather conditions.

How Vanadium Redox Flow Battery Works?

A VRFB comprise power cells in which a proton exchange membrane separates electrolyte chambers. Vanadium is the electrolyte on both sides. VO2+ and VO2+ ions exist in the electrolyte in the positive half cell. V3+ and V2+ ions exist in the negative half cells. A vanadium pentoxide (V2O5) solution forms electrolytically by dissolving it in sulfuric acid. This means the solution is highly acidic.


In vanadium redox flow batteries, both half cells are linked to pumps and storage tanks. The huge volume of electrolytes can circulate into and out of the half cells. The operation needs circulation of huge liquid electrolytes volumes. That prevents the vanadium flow redox batteries being workable in mobile applications. Moving acid liquids is awkward, meaning VRFB get used more in huge stationary installations.


The VO2+ ions in the positive cells translate across to VO2+ ions during the charging process. Electrons move away from the positive terminal of the battery. In the same way, electrons in the negative half-cells translate the V3+ ions into V2+. The process reverses in use giving a traditional open circuit voltage of 1.41 volts at temperature 25 degrees centigrade.

Vanadium Redox Flow Battery

Where Does Vanadium Redox Flow Battery Work?

VRFB is a new type of rechargeable battery for solar. The advantage of the VRFB is that it can hold an unlimited capacity of energy. To add storage capacities simply increase the electrolyte storage tank size. VRFB can remain discharged for a long time without adverse effects. If the electrolytes mix, the battery isn't affected.


The state of charge between a pair of electrolytes affects the capacity degradation. It is different with a single cell in non-flow batteries. In VRFB, the electrolyte is aqueous, non-flammable and safe. The newer generation VRFB uses a mixed solution of acid and so operates over a broader range of temperature. This fact allows self-cooling of the VRFB.

Vanadium Redox Flow Battery

Vanadium Redox Flow Batteries Pros & Cons

Pros include:

  • Their power and energy rating is decoupled using a variable tank size
  • The battery is suited for larger capacities
  • There are low energy related costs ($/kWh)
  • The VRFB can use a larger part of its gross (battery) capacity
  • VRFB perform more than 10,000 cycles without significant capacity deterioration 
  • VRFB technology is resistant against deep discharge

Cons include:

  • A significantly lower efficiency
  • Higher power related costs ($/kW) 

When Are Vanadium Redox Flow Batteries Used?

The environmental impact of Vanadium Redox Flow battery technology is beneficial. This is true with vanadium solution having a long life. Vanadium is a reusable and recyclable material. The VRFB technology is improving so these batteries are available for residential solar storage.


Compared against enclosed batteries VRFB have fewer options for use. Vanadium Redox Flow Batteries viability increases with scale. Above a minimal benchmark capacity of energy storage they start to become effective.


It is likely that battery makers will address the issue of cost with greater volume in the market. That may also address comments about electrolyte feedstock materials price fluctuation in the manufacturing process. It would mean the cost per stored watt falls in the long term and cost-efficiency improves when the VRFB becomes widely used.


Vanadium based batteries are effective technologies for solar storage. As the technology refines to becomes efficient VRFB will become a common solar storage option. Global consumption of energy grows so it’s critical to use existing energy resources effectively.


There will be growing levels of political and financial support for renewables like solar power. Even unpopular energy sources, like nuclear power, opposed on environmental reasons, will find favor if reliable options for power supply start to falter.

Vanadium Redox Flow Battery

Conclusion & Future Of Vanadium Redox Flow Battery

Battery innovations often lead to improvements during battery commercialization. As momentum builds, future work in durability, efficiency, and operational cost-effectiveness of the improved technology becomes viable.


German researchers, Martin Uhriga, Sebastian Koeniga, Michael R. Suriyaha, and Thomas Leibfrieda, who presented a paper to the 10th International Renewable Energy Storage Conference in March 2016, concluded that in general, VRFB home storage systems are still not economically viable to use with today's system prices.


Enhancement of renewable solar energy storage technologies comes with the use of VRFB. Storage becomes a consideration for keeping our distributed electricity grid supply stable. Large scale battery storage needs to be part of utility planning for those electrical grid networks.


Large-scale commercial solar facilities could prove VRFB for solar storage. The outcome could showcase the viability for renewables getting used for base load electricity supply. As such they might mitigate the requirement for a thermal-based spinning reserve.


I hope that you learnt something from this article. If you want a more in-depth discussion on Vanadium Redox Flow Batteries, check out this book on Amazon.


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References:

INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Research (wileyonlinelibrary.com). DOI: 10.1002/er.1863

https://www.sciencedirect.com/science/article/pii/S0960148117307462

http://www.createdigital.org.au/new-tech-sustainable-batteries/

https://www.researchgate.net/publication/311002656_Lithium-based_vs_Vanadium_Redox_Flow_Batteries_-_A_Comparison_for_Home_Storage_Systems

http://www.irena.org/-/media/Files/IRENA/Agency/Publication/2018/Jan/IRENA_2017_Power_Costs_2018.pdf

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