Australia needs better ways of storing renewable electricity for later. That’s where ‘flow batteries’ can help

As more and more solar and wind energy enters Australia’s grid, we will need ways to store it for later.

We can store electricity in several different ways, from pumped hydroelectric systems to large lithium-ion battery systems. We can also use flow batteries. These are a lesser-known cross between a conventional battery and a fuel cell.

Flow batteries can feed energy back to the grid for up to 12 hours – much longer than lithium-ion batteries which only last four to six hours.

I was one of the inventors of one of the main types of flow battery in the 1980s. It has taken decades to bring batteries like these to commercial viability. But they are, finally, arriving in earnest.

This year, the Australian government launched a national battery strategy to expand domestic manufacturing of batteries. This A$500 million strategy will focus on the well-known lithium-ion batteries which power phones and cars. But it will also include flow batteries.

Batteries are becoming more and more important. They can now power cars, houses and even cities. Huge amounts are being spent on commercialising new battery chemistries to electrify transport and make it possible to green the power grid.

To date, most of Australia’s grid-scale batteries use chemistries such as lithium-ion. But as our grid shifts to renewables, we’ll need longer duration storage to eliminate the need for fossil fuel backup generators. That’s a task well suited to flow batteries.

What makes flow batteries different?

Conventional batteries such as lithium-ion batteries store power in their electrodes, commonly a metal.

Flow batteries store power in their liquid electrolytes. Electrolyte solutions are stored in external tanks and pumped through a reactor where chemical reactions take place at inert electrodes to produce energy.

Flow batteries can be altered to suit requirements of a task. You can change how much power you generate (in kilowatts) and how much storage (in kilowatt-hours). If you want more storage, you increase the volume of electrolytes in the tanks.

As you increase storage capacity, the cost per kWh of stored energy decreases dramatically. This is because you only have to add more liquid electrolytes rather than adding entirely new battery packs, as in conventional batteries.

This means flow batteries are currently the cheapest way to store electricity for longer durations (over 8 hours). Unlike lithium-ion batteries, flow batteries can run for tens of thousands of cycles and the electrolyte can last much longer – or even indefinitely. One downside is their weight – these batteries are very heavy and are not portable.

To date, zinc bromine and vanadium redox batteries have undergone the most testing and commercial implementation.

Vanadium flow

In the mid-1980s, my colleagues and I pioneered vanadium redox flow batteries at the University of New South Wales. Vanadium is an unusual metal. It can exist in different states of oxidation in the same solution. That means you can run a battery using just one element, instead of two, as in other chemistries. Doing so lets you avoid cross-contamination and gives the electrolyte solution an indefinite life.

After decades of development, vanadium flow batteries are now being commercially produced by companies in Japan, China and Europe, with several gigawatt hours worth of capacity now installed globally.

China, the world’s largest vanadium producer, has recently approved many large new vanadium flow battery projects. In December, the world’s largest came online in Dalian, China, with 175MW capacity and 700 mWH of storage.