Proponents of the metal vanadium believe it will improve the economics of wind and solar power enough to make them cost-competitive with fossil fuels. Batteries using vanadium have the right combination of scaleability, power and discharge/recharge characteristics to store wind and solar power until it can used during peak demands when prices are highest.
These proponents include promoters, such as the companies developing them for commercial markets, and scientists, including those at the U.S. Department of Energy (DoE).
- The promoters proclaim vanadium is “the next big thing” in energy storage.
- The scientists are more cautious but optimistic: With just a little more work, the vanadium battery “could potentially increase the use of wind, solar and other renewable power sources across the electric grid."
Traditionally, pumped hydro systems and compressed air systems have been considered the best candidates for storing wind and solar power.
- Pumped hydro has been used for non-renewable energy storage for many years, but requires specific topography and huge, expensive tracts of land.
- Only one project in the U.S. uses compressed air energy storage (CAES) and a small handful of others are being developed, but CAES requires specific and rare geologic formations as well as major capital investment. (E•BOOM CAPITAL recently analyzed CAES and listed major players here.)
In the past couple of years, technology known as flow batteries have taken center stage as the best hope for batteries to meet the requirements of renewable storage. And the best of the flow battery technologies is vanadium redox flow batteries (VRFB), according to the various DoE analyses which describes them as “the most promising” and the “best performing” with “enormous potential”.
Vanadium is being compared with lithium for its unique characteristics. Small and high-powered batteries based on lithium are a critical enabling component of smart phones and laptop computers and may be -- if the cost can be reduced -- the key to battery-powered vehicles. Now vanadium is proclaimed as bringing critical enabling performance to wind and solar power storage.
A conventional battery is an electrochemical system that converts chemical energy to electrical energy. Unlike conventional batteries that store their reactive materials within the cells, a flow battery stores electrolytes in tanks, one for positive reactions and another for negative. When energy is needed, pumps flow the electrolyte over opposite sides of a thin membrane where a chemical reaction produces electricity.
In the VRFB, the electrolyte is vanadium in both the positive (vanadium ion V5+) and negative (vanadium ion V2+) tanks, which prevents cross contamination by diffusion of ions across the membrane. The term “redox” comes from the capacity of the vanadium electrolyte to change its oxidation state (Oxidation is an increase in oxidation, while reduction is a decrease in oxidation).
To charge the battery, electricity is sent to the VRFB’s stack. This causes a reaction that restores the original charge of vanadium ions. The electrolytes with their respective ions are pumped back into to their tanks, where they wait until electricity is needed and the cycle is started again.
According to scientists at the DoE’s Pacific Northwest National Laboratory at Richland, Washington, the VRFB has been limited by its inability to work well in wide range of temperatures and by its high cost. However, these scientists say that modifying the VRFB’s electrolyte solution “significantly improves its performance”.
The scientists found that adding hydrochloric acid to the sulfuric acid typically used in vanadium batteries increased the batteries' energy storage capacity by 70 percent and expanded the temperature range in which they operate.
"Our small adjustments greatly improve the vanadium redox battery," said lead author and chemist Liyu Li. "And with just a little more work, the battery could potentially increase the use of wind, solar and other renewable power sources across the electric grid."
The DoE lab’s latest work is detailed in a paper published in the March 2011 edition of the journal Advanced Energy Materials.
Tomorrow: No Utilityl-Scale VRFB Projects in Sight
Photo credit: Pacific Northwest National Lab
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