New Flow Battery Deploys Salt For Long Duration Energy Storage

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Back in the early 2000’s, low cost natural gas began to chase coal out of the US power generation business. Now low cost renewables are are beginning to edge gas power plants aside, with an assist from new energy storage systems. Pushing those storage costs down will help kick the energy transition into high gear, and the Dutch flow battery startup Aquabattery expects plain old table salt to do the trick.

A Salty New Flow Battery For Long Duration Energy Storage

If you’re thinking that new sodium-ion battery technology is in the mix, that’s a pretty good guess. Researchers have been eyeballing sodium to replace the lithium in Li-ion electric vehicle batteries, but that’s not the kind of energy storage system up Aquabattery’s sleeve.

Aquabattery specializes in flow battery technology, which leverages the chemical reaction that occurs when two specialized liquids are set in motion together, separated only by a thin membrane.

Talk of a flow battery electric car has come across the CleanTechnica radar now and then, but the main focus of flow battery attention is on stationary, long duration energy storage systems that could reduce the need to build new gas “peaker” plants, if not eliminate them altogether.

Flow batteries sport several advantages over conventional Li-ion battery arrays for stationary energy storage. For starters, they can deploy non-toxic, non-flammable, earth abundant materials, which drives down costs on the supply chain end.

Flow batteries are also relatively easy to scale up or down, by strategically adjusting the size of the holding tanks.

Aquabattery describes its signature technology as an “acid-base flow battery based on reversible water dissociation.”

“The battery stores electricity in the form of chemical energy in acid, base and saltwater solutions, which are kept in separate tanks,” the company explains. “Pumps circulate these fluids through a power stack with electrodes separated by membranes. The membranes allow ion exchange between electrolytes to generate electricity.”

As for scalability, Aquabattery has that covered:

“The power output depends on the surface area of the electrodes, while the storage duration depends on the electrolyte volume. This makes flow batteries easily customisable and suitable for long-duration applications and utility-scale deployment.”

The Search For The Perfect Flow Battery

The leading Norwegian energy firm Statkraft has been on the prowl for long duration energy storage solutions that fit the needs of the European energy market. Typical Li-ion arrays last for 4-6 hours. Flow batteries and other new long duration technologies provide for 8 hours and up, including days and weeks on end.

Statkraft already has a long, deep footprint long duration energy storage, through its holdings in the hydropower business. However, hydropower is limited by geography and water availability. Flow batteries would provide Statkraft with a far wider range of storage opportunities, in addition to avoiding the consequential infrastructure and geoengineering required of new hydropower systems.

If you’re wondering why not just build bigger arrays of Li-ion batteries, that’s a good question. Statkraft has assessed that Li-ion technology useful in some contexts, but not others.

“Lithium-ion batteries are first and foremost a good solution for short-term balancing in the grid, from a few seconds to an hour,” explains Matthias Holzenkamp, who is the head of commercial asset management of Statkraft’s German branch.

“The batteries are able to deliver large amounts of power in a short period of time, and are therefore very effective in dealing with short-term fluctuations in the power supply,” he adds. “Batteries may also be relevant for balancing in the course of a day, but then they often compete with other, cheaper technologies.”

Holzencamp sees a continued use for conventional batteries in regions where the availability of wind or solar energy is fairly consistent. However, the need for long duration energy storage is clear in Europe, where weather patterns are more variable.

“The European market primarily needs long-term flexibility over days and weeks,” he emphasizes. “For example, if you store power to compensate for a week without sun, you need a huge battery, and it wouldn’t be profitable because the battery is rarely used,” he says. “Batteries are very expensive and therefore need many operating hours to pay off.”

Statkraft Meets Aquabattery

Many new and different flow batteries have been emerging from the lab in recent years, including a zinc-bromine formula first explored by Exxon back in the 1970’s.

Statkraft appears to have found what it is looking for in Aquabattery. Last week the two companies announced a new partnership aimed at pilot-testing Aquabattery’s table salt flow battery at a location in the Dutch city of Delft.

If all goes according to plan, the energy transition payoff will be significant.

“Long Duration Energy Storage can be used for shifting energy from peak to low generation hours and to defer costly grid infrastructure investments. It may also alleviate grid congestion which is a problem in many countries today and hinders wind and solar plants from connecting to the grid,” Statkraft explains.

We’ll find out soon enough. The pilot test is expected to last 6-12 months and yield enough information to assess the system’s scalability and suitability for commercial application.

Statkraft anticipates that Aquabattery’s flow battery will provide for long duration energy storage at a minimum of eight hours for starters, on up to “multiple days or weeks.”

USA Catches Flow Battery Fever

Flow batteries would also be a good fit for the US market, and the US Army is already laying plans to share the flow battery love. Earlier this year the Army began testing flow batteries developed by Lockheed Martin at Fort Carson in Colorado. If they like what they see, flow batteries could be installed at Department of Defense facilities around the world as well as here in the US.

The US Department of Energy is also on the case. The agency’s Argonne National Laboratory, for example, has been assessing the behavior of flow batteries in microgrids with an eye on widespread adoption for EV charging stations.

Last July the Energy Department issued a ringing endorsement of flow battery technology in its new Findings from Storage 2030 report. “With the promise of cheaper, more reliable energy storage, flow batteries are poised to transform the way we power our homes and businesses and usher in a new era of sustainable energy,” the agency enthused.

That remains to be seen. However, the Energy Department also lists several significant new commercial flow battery deployments in the US and elsewhere, indicating that the industry is ready for prime time.

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Image: The leading Norwegian energy firm Statkraft has partnered with the Dutch startup Aquabattery to assess the performance of a flow battery based on table salt (courtesy of Aquabattery).