Redox flow batteries for energy storage

We assess the companies and projects in the flow battery market: from vanadium redox battery technology to zinc bromide, iron chromium, zinc iron and beyond. Photo credit: Sumitomo Electric
We assess the companies and projects in the flow battery market: from vanadium redox battery technology to zinc bromide, iron chromium, zinc iron and beyond. Photo credit: Sumitomo Electric
Flow batteries: the market, companies and projects, from vanadium redox battery technology to zinc bromide, iron chromium, zinc iron and beyond. Photo credit: Sumitomo Electric

Flow batteries: the market, companies and projects, from vanadium redox battery technology to zinc bromide, iron chromium, zinc iron and beyond. Photo: Sumitomo Electric

The quest continues for reliable grid-scale energy storage that does not involve huge civil engineering projects.

Current bets are on shipping containers full of lithium-ion batteries (courtesy, no doubt, of the gigafactories predicted to be springing up all over the US in the next few years) as last year’s excitement over compressed air energy storage has now, well, deflated.

There is another technology that shows some promise, however. Redox flow batteries may not yet be ubiquitous, but they are making a global impact, are attracting investment and do seem to work.

So let’s start with a brief roundup of some of the larger projects currently in operation.

Current large-scale energy storage

Japan has the two biggest installations. Tomamae wind farm on Hokkaido Island, whose 4MW of storage is used to smooth out wind-generated energy peaks and troughs, is the first.

The second is something of a showcase, being at manufacturer Sumitomo’s head office in Osaka, which provides 3MW peak shaving. Another 1MW installation at Yokahama Works stores renewable generated electricity.

All three of these projects are by Sumitomo. In China, the Zhangbei National Wind and Solar Energy Storage and Transmission Demonstration Project has a 2MW vanadium redox flow battery provided by Prudent Energy.

The company also supplies an additional 500kW of flow storage to help ensure grid stability. Plus Prudent provides the current largest flow battery project in the US.

Its Vanadium Redox Battery Energy Storage System provides 600kW at Gills Onions, California, storing energy produced from the methane generated from bio-waste.

Here, flow battery energy storage helps save money through avoiding peak-hours grid energy charges.

The Indonesian island of Sumba’s population is now overcoming the idiosyncrasies of the grid thanks to yet another Prudent Energy installation, this time weighing in at 400kW.

Changing trends?

To date, the largest flow battery projects around the world are notable for three things. The chemistry is dominated by vanadium. In fact, all the projects above involve vanadium redox flow batteries.

Secondly, Prudent Energy dominates the field for larger projects. And lastly, even the bigger projects are, well, not that big, with the largest currently a mere 4MW. Is this picture likely to change? Taking the aspect of capacity first, there’s no reason why not.

Although they require a larger footprint than lithium-ion batteries overall, flow batteries tend to be more scalable, in essence simply requiring bigger or more tanks to contain a greater volume of electrolyte.

Bigger and better redox flow batteries

Taking a look at projects now in the pipeline, it does indeed look like flow battery projects are getting more ambitious. And it seems some of the action, at least, is moving west.

A 28MW project has been announced for Modesto in California, while Primus Power is providing 25MW to the same site for a project currently under construction to deal with the intermittency of the area’s wind and solar energy resources.

Meanwhile, back on the Japanese island of Hokkaido, the Minami Hayakita substation is planning 15MW more of Sumitomo storage.

Alternatives to vanadium

Besides scale, and manufacturer, the first two of these projects also mark a change of chemistry, as neither are vanadium redox flow systems. The first is zinc bromide, the second a zinc-chlorine redox flow battery.

Developing technologies that are not vanadium dependent appears to be a smart move, as it is far from plentiful or cheap.

This is not a problem for CellCube redox flow battery manufacturer and distributor, American Vanadium, which owns a very big vanadium mine, the only one in North America, in fact.

Irrespective of whether or not the company decided to get into the flow battery industry to find a use for its vast mineral assets, the CellCube is certainly being taken seriously.

Deployments include a two-year trial in the New York City Metropolitan Transportation Authority headquarters in Manhattan.

But if you don’t have a requisite hole in the ground and you are not in the business of using vanadium recovered from abandoned oil wells and mine tailings, as Imergy Power Systems claims to do, you might want to look for alternative chemistries.

Zinc-bromide flow batteries

In fact zinc-bromide redox flow batteries are already fairly prevalent across smaller-scale projects globally. RedFlow has over 100 projects, mainly in Australia but also in New Zealand and the US, delivering building-level energy storage.

The Brisbane-based company recently made the news by attracting a USD$2.2m cash injection from investor Simon Hackett.

Perhaps better known, ZBB Energy Corporation has a whole slew of installations from US naval base microgrids to data centre UPS systems, principally in the USA.

Iron-chromium redox flow batteries

Another chemistry to recently make the headlines is the iron-chromium redox flow battery, from EnerVault.

The company’s first-of-its-kind facility is on an almond farm in California, where the 250kW battery will store solar energy from a nearby array and drive a large irrigation pump.

This is, strictly speaking, a demonstration project and was made possible partly through funding from a US Department of Energy American Recovery and Reinvestment Act grant.

It is hoped the project will show that this form of energy storage can live in harmony with a solar energy source as part of a real-life commercial application.

EnerVault chief executive Jack Pape also likes to think it will prove you don’t need a $5bn gigafactory to make energy storage a massive success.

His business model involves largely off-the-shelf components such as tanks, pumps and controls, and illustrates the relative simplicity and modular scalability of flow battery technology.

Zinc-iron redox flow batteries

Another company betting on an alternative to vanadium is ViZn Energy, formerly Zinc Air, Inc. The company has developed its own zinc-iron redox flow battery technology, aimed at a wide field of applications, including the microgrid market.

It has raised capital from a group of wealthy backers, currently has no debt and has very recently won the 2014 Intersolar Europe Electrical Energy Storage Award for its Z20 energy storage system. These products are currently shipping and being deployed.

For more exotic species of flow battery, you need to take a peak inside the lab.

MIT organic flow battery

Last year, for example, Massachusetts Institute of Technology (MIT) announced it had developed a battery that used laminar flow to keep its electrolytes separate, thus avoiding the need for a membrane, which is often the most costly part of a redox flow system.

The MIT membrane-less battery has at least one disadvantage, however: its use of hydrogen bromine, which although plentiful and inexpensive is highly corrosive, and the reason the team attempted to do without the membrane in the first place.

Another research project, this time from Harvard, uses inexpensive organic molecules called quinones to dispense with metal ions and expensive catalysts altogether.

It’s innovations such as these that could drive down the costs further, while the natural advantages of low-cost scalability and off-the-shelf engineering may mean that, one day, grid-scale energy storage will truly go with the flow.

Written by Mike Stone

2 Comments on "Redox flow batteries for energy storage"

  1. A good summary. Many of these projects (and a few new developments) will be discussed at next month’s International Flow Battery Forum, in Hamburg, Germany.

    • Keith Bithell | March 15, 2015 at 11:26 pm | Reply

      Great summary, I believe that whilst Prudent Energy dominate large scale applications they are actually using Sumitomo technology under an agreement.

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