Energy Storage: Vanadium Redox Flow Batteries

The challenge of using renewable energy sources such as solar power and wind power as a potential means of supplying electricity is overcoming the intermittent nature of the source. Solar power cannot be produced at night and wind power requires a sufficient level of wind to be blowing before electricity can be generated.

Even when there is sufficient wind or sunlight available, the unreliability of the flow is still an issue. Wind gusts will cause unexpected surges in the production of electricity which is fed into the grid which must be regulated in some way.

A means of energy storage and subsequent modulation is required that is large enough and cost effective enough to ensure the power grid remains adequately fed. It needs to be efficient, resilient and reliable. Energy storage is also becoming a government requirement as can be seen by a recent decision by California.

One of the ways in which renewable energy performance is going to be improved is through the development of storage methods such as vanadium redox flow batteries. These batteries have been proven to work in smaller scales and have been stacked to operate just as effectively in larger systems. In fact, the scalability of these systems is one of the advantages of using them and due their cost effectiveness, it is possible that their use will continue to expand, particularly with the improvements that are ongoing.

What Are Vanadium Redox Flow Batteries?

These batteries are rechargeable flow batteries that use vanadium ions in different oxidation states to store energy. They consist of power cell assemblies containing electrolytes separated by a proton exchange membrane. Chemical energy is converted to electrical energy, a process which can also be reversed if required.

The word redox is derived from the process of reduction oxidation which is the process of electron uptake / electron release that occurs in the flow cell. Energy storage takes place in electrolyte solutions contained in tanks.

It is the electrolytes that are vanadium based with one side containing positive vanadium ions and the other containing negative vanadium ions. The half cells are connected to storage tanks and pumps to allow the electrolytes to be circulated through the cell.

Vanadium Redox Flow Battery DiagramThe capacity of the vanadium redox flow battery is that it can be almost unlimited in its capacity. By simply making larger and larger storage tanks the capacity can be increased.

Where this type of battery can fall short is in its poor energy-to-volume ratio, however there has been continued improvement in how they are being built and the composition of the electrolytes that are used in the half-cells.

What Are the Benefits of Using Vanadium Redox Flow Batteries?

  • Energy density is increased by more than 70% due to increased vanadium ion concentrations
  • Allows for operation at increased current densities
  • Increases the operating temperature window by more than 83%, reducing air conditioning costs and increasing energy output
  • Could potentially store megawatts/ megawatt-hours of power and energy in simple designs
  • Allows the flexibility to design power and energy capacities separately
  • They can be customized to suit a range of different storage situations
  • Can discharge power for up to 12 hours at a time
  • Can be quickly brought up to full power when needed (i.e., in subseconds)
  • Offers a long cycle life (>5,000 deep cycles) due to excellent electrochemical reversibility
  • Offers high energy efficiencies
  • Does not present a fire hazard and uses no highly reactive or toxic substances, minimizing safety and environmental issues
  • They can sit idle for long periods of time without losing storage capacity

How Are Vanadium Redox Flow Batteries Being Improved?

VRBs usually require expensive polymer membranes due to the highly acidic and oxidative environment, which lead to high system costs. The low energy densities and small operating temperature window, along with high capital cost, make it difficult for the current VRBs to meet the performance and economic requirements for broad market penetration.

A new electrolyte solution is currently being developed by researchers at Pacific Northwest National Laboratory consisting of a mixture of sulfate and chloride. This solution can hold more than 70% more vanadium ions than the pure sulfuric acid which is typically used. This new solution also increases the operating temperature window by 83%.

New Japanese Installation Proposed

There has been a recent announcement in Japan that a new vanadium redux flow battery is going to be built in Hokkaido. Not only is it going to be a storage system to smooth out the production of renewable energy but it is going to be the largest battery storage system in the world.

The project is a joint development between Sumitomo Electric Industries Ltd and Hokkaido Electric Power Co. Hokkaido Electric will build the battery system that has been produced by Sumitomo at a substation in the town of Abira.

Funding for the project is being provided by Japan’s Ministry of Economy, Trade and Industry to the tune of ¥20 billion which will be provided to cover all development and manufacturing costs.

To date electricity generated from renewable sources accounts for only 1.6 per cent of the nation’s total. It is the belief of the ministry that by using these types of batteries utilities will be able to buy 10 per cent more electricity from renewable energy sources.

Further Reading

Follow the links provided below to find out more about Vanadium Redox Flow Batteries.

Science Daily – Breakthrough in electricity storage

Pacific Northwest National Laboratories – Upgrading the vanadium redox flow battery

Project In New York Will Put Vanadium Flow Batteries to the Test

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