Flow battery manufacturers typically pursue utility scale storage projects but German start-up VoltStorage is targeting the household market.

Vanadium redox flow batteries are big business, as the $70 million merger which formed Invinity illustrated.

Munich-based residential vanadium redox flow battery start-up VoltStorage has secured another $7 million from investors including the Bayern Kapital subsidiary of the development bank of Bavaria; family investment house Korys; the EU-backed EIT Innoenergy, New Jersey-based venture capital fund and seed investor SOSV and Zurich power company Energie 360.

The firm claims its flow battery system can complete more than 10,000 charge cycles without any effect on capacity and says its electrolyte is a recyclable, non-flammable vanadium solution. VoltStorage’s modular unit reportedly offers a continuous power rating of 1.5 kW and nominal energy of 6.2 kWh. The unit comes with a ten-year warranty.

More than 20 flow battery chemistries, including zinc-bromine, zinc-iron, zinc-cerium and magnesium-vanadium have been studied with vanadium redox the closest to wide commercialization. Vanadium, the dominant cost in the electrolyte, is a metal mined in Russia, China and South Africa although there are reserves in the U.S. and Canada. It is used predominantly as a steel additive. Flow battery manufacturers include Washington-based UET, Montana’s Vizn, California-based Primus, Japan’s Sumitomo, Anglo-Canadian Invinity Energy Systems – formed after the recent merger of California’s Avalon and U.K.-based redT – and Form Energy

Flow batteries circulate a liquid electrolyte through stacks of electrochemical cells and have long held the promise of 10-hour duration, tens of thousands of cycles, minimal degradation and no limitation on depth of discharge. That performance promise has lured venture capital investment and R&D but, thus far, the support has yielded few competitive commercial flow batteries.

Vanadium flow battery manufacturers have aimed for mass-commercialization of their longer-duration systems for 20 years but have never been able to reach volumes of scale. The steep fall in the price of lithium ion batteries has not helped market penetration for rival technologies. Bermuda-based asset manager Lazard has calculated, however, the levelized cost of storing electricity in some redox flow projects now overlaps that of lithium-ion batteries. Lazard said sales of vanadium flow batteries have grown from double digits to just over 200 MWh of installed storage capacity. That figure is still meager, though, alongside the volume of lithium ion storage deployed.

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