Redox Flow Batteries: For Grid Level Storage

by Chad Redman

Current energy storage technologies are often overlooked in favor of the next promising development that will be commercialized sometime in the future, but economical large scale energy storage is already possible with current equipment. Redox flow batteries (RFBs) are a type of large battery that utilizes reduction and oxidation reactions to charge and discharge liquid electrolyte solutions. The advantage of RFBs over other battery types is realized in scale; RFBs can easily expand and store more energy by using larger storage tanks for the electrolyte solutions. However, the power that can be produced by an RFB is determined by the architecture of cells within the RFB. Unlike a standard Li-ion or lead-acid battery, only a small percentage of the energy within an RFB is accessible as power at any given moment.

RFB development has produced three separate flow battery technologies in recent years. The first of these is the Iron-Chromium (ICB) flow battery. This battery type employs iron and chromium as electrolyte fluids, and has the advantage of being reliable relative to other RFBs. However, ICBs come up short on the power density front, making them less promising in the long-run. Interestingly, the Electric Power Research Institute supported ICB technology in 2010, showcasing its safe, reliable, and cost-effective nature.

Two other RFB types are under development, each boasting much higher energy densities than ICBs, but each being less reliable, less safe, and more expensive to operate. Both vanadium redox flow batteries and zinc-bromine flow batteries are capable of being charged to such a power-dense state that the cells and membranes within the batteries deteriorate and fail. As these technologies improve, they will replace ICBs as a more effective form of RFB.

“Redox Flow Batteries.” EnergyStorage.org. N.p., n.d. Web. 09 Feb. 2015.

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