Flow batteries: how they work and Australia's prospects

As the world searches for safe, low-cost big batteries, an old Australian invention is getting new attention

In late September, a new power station opened in Dalian, northeastern China.

It’s a big battery – but it doesn’t look much like one that Tesla would sell you. The station is filled with tanks and pumps, moving liquids filled with vanadium throughout the facility. The only lithium to be had is in the phones of the staff operating the plant.

It’s a “flow battery”: a 40-year-old Australian invention that is receiving renewed focus as our energy grids transition.

Large white tanks, several metres high, containing flow battery electrolytes
The tanks containing electrolyte for the flow battery. Credit: DICP

How flow batteries work

Flow batteries were first developed in the 1980s, by now-Emeritus Professor Maria Skyllas-Kazacos at the University of New South Wales.

“Most of the batteries that we use are enclosed systems,” says Associate Professor Alexey Glushenkov, a chemist and research lead in battery materials at the Australian National University’s Battery Storage and Grid Integration Program.

In conventional batteries, the metals and salts that react to make electricity are all held in the one unit: the anode supplies electrons into an external circuit on one side, and the cathode accepts them on the other.

This is called a reduction-oxidation, or redox, reaction.

Flow batteries use the same chemical principle – they’re also called redox flow batteries – but their physical structure is different.

“Flow batteries have a different system that consists of two parts,” explains Glushenkov.

Diagram showing components of redox flow battery
Schematic of a redox flow battery. Credit: Weber, A.Z., Mench, M.M., Meyers, J.P. et al. Redox flow batteries: a review. J Appl Electrochem 41, 1137 (2011). https://doi.org/10.1007/s10800-011-0348-2

First there’s the reactor, hosting an anode and a cathode, where the electricity-generating reaction takes place. An anolyte and a catholyte – two liquids – are pumped through this.

“The second part of a flow battery is actually tanks of these electrolytes,” says Glushenkov.

“You pump the two liquids through the reactor, and their oxidation state changes when they’re in contact with the electrodes.”

Electrons and ions are transferred between the anolyte and the catholyte, and electricity flows. The batteries can be charged and discharged by pumping the electrolytes back and forth.

The most promising flow batteries have both their anolytes and their catholytes filled with dissolved vanadium: specifically, V2+ and V3+ ions.

Providing when lithium doesn’t (and not providing when it does)

This liquid vanadium dodges three of lithium-ion batteries’ most pressing problems: price, safety, and longevity.

The price and safety of the batteries are better simply because they don’t have lithium in them – an energy-dense, but reactive and resource-strained material.

But the longevity is thanks to the vanadium itself.

“There’s no consumption or degradation at all of that solution, because you’re either in one form of vanadium or the other,” says Vincent Algar, managing director of resources company Australian Vanadium.

“So the nature of that vanadium flow battery is that it doesn’t consume any of its reagents – you’re not going to get any reactions taking place which might destroy the cell over time.”

Person in a hard hat operating a computer panel among a wall of large batteries
System debugging on the Dalian battery. Credit: DICP

Warranties on big lithium-ion batteries are around 15-20 years. Vanadium flow batteries could, theoretically, last indefinitely.

Matt Harper, chief commercial officer at vanadium battery manufacturer Invinity, says that their batteries are expected to last at least 25-30 years, based on the tests they’ve run and batteries that are still performing after five or six years.

While he’s confident in their data, “the only way to figure out the battery’s really going to last 30 years is to run it for 30 years,” he says.

“The only way to figure out the battery’s really going to last 30 years is to run it for 30 years.”

Matt Harper

So: what’s the catch?

“They have less energy density. Therefore, to build a comparative battery you need to make it very, very large,” says Glushenkov.

Aerial shot of dalian flow battery energy storage peak-shaving power station
The Dalian vanadium flow battery station. Credit: DICP

The Dalian station boasts a current capacity of 100 MW/400 MWh, which will eventually be expanded to 200 MW/800 MWh. Australia’s biggest operating battery, lithium-ion and taking up about the same space, is 300 MW/450 MWh.

Flow batteries also can’t be superior in power – kilowatts – but they can do better in energy storage. – kilowatt-hours.

“Our fleet, our phones, our devices, are all going towards lithium-ion: that’s become a power problem,” says Algar.

“But when we talk about changing our grid, to be able to handle all the renewable energy that we’ve currently got coming into it, we need to think about energy storage.”

“When we talk about changing our grid, to be able to handle all the renewable energy that we’ve currently got coming into it, we need to think about energy storage.”

Vincent Algar

Over a longer period of time – say, a night instead of a few hours – vanadium flow batteries are cheaper grid additions.

“The crossover point is, we think, about six hours at the moment, where the economics of using vanadium is better than lithium,” says Algar.

“Lithium-ion batteries do a really good job at replacing the gas-powered generators that run for something like 500 hours a year,” says Harper.

“Whereas what we look at is using the combination of our batteries and renewable power to provide baseload power.”

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The batteries getting built

In late November, energy company North Harbour Clean Energy announced plans to develop what will be Australia’s biggest flow battery, at a modest 4 MW/16 MWh, alongside a manufacturing line in Eastern Australia.

Invinity is further along the line, currently shipping a battery half the size to Yadlamalka, north of Port Augusta in South Australia.

Originally slated to be done by the end of 2021, the project was delayed after heritage assessments on the original site for the battery found a large number of Aboriginal artefacts.

Having found a new location, the project is now expected to be operational early next year. It will be a 2 MW/8 MWh addition to the grid.

“What we look at is using the combination of our batteries and renewable power to provide baseload power.”

Matt Harper

“The project that we’re building at Yadlamalka, I think, is a perfect example of where the technology fits well,” says Harper.

It’s a place with abundant solar energy, that could do with some more overnight storage – as is evident from Port Augusta’s revived solar thermal hopes.

“Remote microgrids are perfect for flow batteries of all scales,” says Algar.

“They’re not temperature sensitive, like lithium-ion batteries, so they can operate quite comfortably in hot conditions, which is a real benefit. And, obviously, they’re non-flammable.”

While China, with nearly half the world’s vanadium, is throwing its efforts behind huge plants, Australia’s first users of vanadium might be farms, mines, and small remote communities.

“Those are all run by diesel right now, yet we’ve got so much renewable resources in those places,” says Algar.

Australia’s first users of vanadium might be farms, mines, and small remote communities.

There’s mining revenue as well as utility to be had here too: Australia has around 18% of the world’s vanadium reserves, mostly in Western Australia – hence Australian Vanadium’s interests. The element is still, mostly, used in steel, but flow batteries are going to change things.

“There’s only a handful of primary vanadium mines in the world at the moment,” says Algar.

“There is going to be a restriction of supply unless some new mines get developed.”

Invinity, conversely, has partnered with wind turbine manufacturing giant Siemens Gamesa: their heightened storage makes flow batteries a better partner for wind projects, which are often much bigger energy generators than solar farms.

“The combination of solar power and batteries together has been a huge story over the last three or four years, but we’re just starting to see the combination of batteries plus wind,” says Harper.

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