A new concept for large-scale redox-flow batteries (RFB) for energy-storage applications has been developed by ThyssenKrupp Industrial Solutions AG (Dortmund, Germany; www.thyssenkrupp-industrial-solutions.com). The system is based on the oxidation and reduction of vanadium ions (diagram, top) for either storing electrical energy (charging), which is produced by renewable sources (solar or wind), or utilizing this energy (discharging) during periods when power generation is interrupted (windless days or nighttime).
The all-vanadium RFB was designed in order to take advantage of economy-of-scale for large flow-through electrochemical cells, said Niels Bredemeyer, senior chemist at the company’s Process Technology business unit, during a congress session at Achema (June 15–19; Frankfurt, Germany). Conventional flow-through cells suffer from large pressure drops, flow mal distribution and a state-of-charge (SOC; remaining capacity of a battery) that depends on the cell height, explained Bredemeyer. These drawbacks are especially problematic when scaling up to large scale, he said.
To overcome these issues, a new and unique flow regime was developed, based on the company’s experience with large-scale electrolyzers for chlor-alkali and HCl production. Instead of electrolyte flowing in the xy -plane as in conventional flow-through designs, the electrolyte is first fed perpendicular to the electrodes (z -direction) through a number of channels (diagram, bottom). This feature results in a lower pressure drop and an SOC that is independent of the cell height, as well as the ability to operate at higher current densities, said Bredemeyer.
Laboratory trials have been performed since 2012 in a test rack with two one-compartment testcells (OCTs) with 0.16-m2 of active area at the Niedersachsen Energy Research Center (EFZN; Goslar, Germany). Data from the test rig have been used as the basis for scaleup to a mid-sized OCT (about 0.7-m2 area), and the company plans to commercialize the technology in 2016, targeting industrial-sized energy storage systems in the megawatt range. This size RFB (2.7-m2area, 20-MW power) is suitable for grid operators, integrated chemical plants and utility companies, said Bredemeyer.
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