As grids absorb more wind and solar, the storage question shifts from power to duration. Flow batteries — which store energy in liquid electrolytes held in external tanks — are emerging as the leading candidate for the hours-long stretches that lithium-ion systems handle less economically.

How a flow battery works

Rather than sealing electrodes inside a cell, a flow battery pumps liquid electrolytes from external tanks through a reactor, where chemical reactions at inert electrodes produce electricity. Capacity is set by electrolyte volume rather than cell count, which means storage can be expanded simply by adding more liquid. The cost per kilowatt-hour of stored energy falls dramatically as duration increases.

The duration economics

Flow batteries can feed power back to the grid for up to 12 hours, compared with four to six hours for typical lithium-ion systems. They are currently the cheapest way to store electricity for durations beyond eight hours, can run for tens of thousands of cycles, and their electrolyte can last far longer — in some chemistries, effectively indefinitely. The trade-off is physical: flow systems are very heavy and not portable, which suits stationary grid assets rather than mobile applications.

Vanadium's origin story

Maria Skyllas-Kazacos and colleagues pioneered the vanadium redox flow battery at the University of New South Wales in the mid-1980s. Vanadium can exist in different oxidation states within the same solution, allowing a battery to use one element instead of two. That avoids cross-contamination between half-cells and gives the electrolyte an indefinite life.

Where the technology stands today

Among flow battery types, zinc-bromine and vanadium redox systems have undergone the most testing and commercial implementation. Vanadium flow batteries are now commercially produced by companies in Japan, China and Europe, with several gigawatt-hours of capacity installed globally. China, the world's largest vanadium producer, has recently approved many large new vanadium flow battery projects.

Demand is not confined to Asia. Australia's grid is shifting toward renewables and needs longer-duration storage to eliminate fossil fuel backup generators, yet most of its grid-scale batteries remain lithium-ion. The Australian government's A$500 million national battery strategy focuses on lithium-ion manufacturing but also includes flow batteries — a signal that the chemistry has moved from laboratory curiosity to procurement line item.

This article was assisted by AI analysis. Please refer to the original source for official information.