Megawatt Ambitions for Vanadium-Based Batteries

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"Vanadium-based liquid batteries under development as scientists strive to build an installation with a capacity of 20 MWh—enough to power roughly 2,000 households through a long winter night."

A Fraunhofer consortium is currently driving the development of large-scale energy-storage systems known as redox flow batteries. The experts' long-term goal is to build a handball-court-sized battery installation with a capacity of 20 MWh—enough energy to provide power to roughly 2,000 households through a long winter night or a cloudy day.

"The process already works reliably," notes Dr. Christian Dötsch, business unit manager for Energy Efficiency Technologies at UMSICHT, one of the participating institutes. "The challenge lies in the upscale version, the enlargement of these plants."

Redox flow batteries are large-scale, vanadium-based liquid batteries in which chemical vanadium bonds alternately pick up and emit electrons along membranes. Because these batteries use only vanadium bonds and not two different fluids at the same time as found in other systems, impurities are eliminated. Dr. Tom Smolinka, in charge of coordinating the work at the Fraunhofer Institute for Solar Energy Systems ISE, states that this exchange makes the batteries more robust.

The vanadium charges and discharges in tiny reaction chambers. One of the challenges is to insure that the vanadium fluid flows smoothly through these large membranes and past the felt-like carbon electrodes in the cells themselves. To accomplish this, Fraunhofer researchers are using flow simulations to improve cell design.

Since last year, the Fraunhofer consortium has also been working on new membrane materials and battery designs in a cooperation project funded by the German federal ministry for the environment. Another project is scheduled to begin this year and will involve industry participation. On principle, batteries with up to 80kW of storage capacity can be built in the new Fraunhofer redox flow laboratory and a 20-kW plant is scheduled to go into operation at the end of next year. The researchers hope to cross the megawatt threshold in roughly five years.

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