flow batteries

Flow batteries are rechargeable batteries in which liquid electrolytes flow through one or more chemical cells from one or more tanks. The electrolytes are redox pairs, that is, chemical compounds that can reversibly undergo reduction and oxidation reactions. The most common redox electrolytes include elements like vanadium, chromium, iron, zinc, and bromine. Flow batteries can provide large amounts of both electrical power and stored energy based on the size of the electrolyte tanks. As a result, they can be scaled up far more readily than other battery technologies.

Flow batteries are safe, stable, long-lasting, and their electrolytes can easily be refilled. They have significant potential for use in utility-scale storage for renewable energy systems.

Researchers at Northwestern University have developed a redox flow battery based on an organic industrial-scale waste product. The material – triphenylphosphine oxide or TPPO – is produced in the thousands of tons each year. It is byproduct of producing a variety of substances including some vitamins, pharmaceuticals, agrochemicals, and other bulk chemicals. For the most part, TPPO is of little use and must be carefully discarded.

The current market for redox flow batteries is very small but is expected to grow over time as the need for utility-scale energy storage continues to expand. A battery technology based on a waste material that is already produced in high volume and that must otherwise be disposed of with caution would have significant advantages.

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Green battery discovery turns trash into treasure

Photo, posted January 12, 2015, courtesy of California Energy Commission via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Lithium-ion batteries power computers, cell phones, and increasingly, automobiles. They started out being rather expensive but have become dramatically cheaper over the last decade, with prices dropping about 90%. Batteries are needed to store clean power from wind and solar generation and lithium-ion batteries are increasingly being used for that purpose as well.

Utility-scale energy storage requires substantial battery installations and battery cost is still very much an inhibiting factor in the widespread adoption of the technology. Lithium-ion battery costs continue to drop but because they require expensive materials like lithium and cobalt, there are limits to how low their prices are likely to get.

As a result, researchers have continued to seek ways to produce batteries made out of cheaper materials. Among the more promising technologies are flow batteries, which are rechargeable batteries in which electrolyte flows through electrochemical cells from tanks.

Flow batteries are much larger than lithium-ion batteries and include physical pumps to move electrolytes. They typically are sold inside shipping containers. Clearly, such batteries are not suitable for use in vehicles, much less in consumer electronics. Nevertheless, they represent a practical option for grid storage.

A company called ESS has developed an iron flow battery suitable for utility energy storage. Clean energy firm CSB Energy plans to install iron flow batteries at several solar projects across the U.S. that will store enough energy to provide power 50,000 homes for a day. According to ESS, the iron-based batteries should sell for about half the price of lithium-ion batteries by 2025 and be able to store energy for longer periods.

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New Iron-Based Batteries Offer an Alternative to Lithium

Photo, posted March 21, 2021, courtesy of Nenad Stojkovic via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A green battery from industrial waste

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Iron Flow Batteries | Earth Wise

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