Flow Batteries: Technology Synergies Will Provide Grid Stabilization

By Lili Francklyn for Micro Grid News

Energy storage technologies appear to be following a trajectory similar to renewable generation. As prices continue to drop and innovative solutions emerge, competition is on the rise and greater efficiencies are created. It’s still early days for the battery market, and a variety of battery technologies are jostling for the leading position.

Aside from the familiar lead-acid batteries that have long dominated the renewable energy market, a few of the most popular are lithium-ion, ion-ferrous phosphate, lithium-iron, and nickel-iron batteries.

While some market-leading battery types struggle with a limited lifespan, thermal runaway (li-ion), depth of discharge (lead-acid), or declining performance (li-ion and lead-acid), the potential advantages of a relative newcomer to the battery scene is becoming more apparent: Flow batteries hold the promise of frequent, virtually unlimited cycling without degradation, which gives them a special niche in energy storage.

Invinity Energy Systems, a company formed recently by the merger of Avalon in the US and Red T in the UK, is a specialist in flow batteries, setting out to popularize flow battery technology, particularly among utility and C&I customers.

Why flow battery technology is well-adapted to utility use

Flow batteries store energy in large tanks of electrolyte fluid that is pumped through electrodes and then pumped back in the recharging process. Sometimes compared to washing machines, flow batteries are the larger, heavier, clunkier cousin of the light, energy-dense lithium-ion batteries that power our electric vehicles, laptops, and phones.

But flow batteries have interesting characteristics that make them an ideal choice for large-scale energy storage. First, the vanadium electrolyte, which is presently used in most flow batteries, can reliably charge and discharge for thousands of cycles without degrading; that’s because of the electrochemical properties of vanadium, which make it very easy to remove electrons from this element and then put them back again.

This means that the flow battery is a workhorse that can cycle for multiple short periods daily, theoretically lasting for 30 years while maintaining an even performance.

The Energy Superhub Oxford will install the UK’s first transmission-connected battery, a lithium-ion/vanadium flow battery, sited at National Grid’s Cowley Substation. | Photo: Energy Superhub Oxford

Big and heavy as they are, flow batteries appear to be a more interesting option for utilities and commercial and industrial customers that are considering extended periods of time for battery use and scrutinizing the value of longer-term investments.

In fact, according to Joe Worthington, Head of External Communications at Invinity, it used to be that the more typical use case for battery storage was one to two hours. Now, he says, “everything in California is up to four hours,” and he predicts that energy designers will soon require six to eight hours of battery use in their projects. Flow batteries do very well with this timeframe, he adds, providing two to ten hours of discharge.

Lithium-ion batteries: A powerful burst of energy

Lithium-ion batteries, on the other hand, have a higher energy density, which means they can deliver a large burst of energy very quickly. They are lighter than flow batteries and more portable, hence their value in electric vehicles and small electronic devices. But, they are volatile, with a tendency to overheat and catch fire. More importantly, lithium-ion batteries degrade as they are used, gradually losing their ability to hold a charge; they can only sustain 300-500 charging cycles or last for four to six years before they need to be replaced.

Oxford, UK: Complementary battery technologies

These two battery technologies and their synergies will come into sharp relief since they are conceived as a “hybrid battery” in a new project in Oxford in the UK, where planners are designing an energy “superhub” that will provide heat, electrify transportation, and decarbonize the grid.

The project will feature a large EV charging network that feeds directly into National Grid’s extra-high voltage transmission network, a system of ground source heat pumps, the unique synergy of flow and lithium-ion batteries, and an energy trading platform.

Invinity will supply a 2 MW flow battery that will provide 5 MWh of power. The main role of the flow battery, explains Matt Harper, Chief Commercial Officer at Invinity, is to act as a giant shock absorber between the grid and variable energy flows that will be created as people plug into the extensive EV charging network.

“What they’re trying to avoid,” says Harper, “is that if you’re going to go [to] the electric grid and inject variable resources and variable loads (such as EVs), you’re going to completely destabilize the supply and demand equation.”

For Energy Suberhub Oxford, the combined lithium-ion and vanadium flow battery technologies create synergies that enable the vanadium flow to do the hard work when providing a Fast Frequency Response service, reducing degradation on the lithium-ion. Photo: Energy Superhub Oxford

For Energy Suberhub Oxford, the combined lithium-ion and vanadium flow battery technologies create synergies that enable the vanadium flow to do the hard work when providing a Fast Frequency Response service, reducing degradation on the lithium-ion. |
Photo: Energy Superhub Oxford

The flow battery, he adds, will be “the tip of the spear” in regulating these sudden changes, so that the grid will remain stable. The flow battery will handle the first 20 minutes of big power fluctuation, but if there is a demand for several hours of power, the lithium-ion batteries will take over.

The flow battery will also be a moneymaker for the project, bidding into the “Fast Frequency Response (FFR)” market up to 15 times every hour, paid by the utility, National Grid, to produce or absorb energy – “upregulation” or “downregulation.”

One other component of the project is a contribution by Habitat Energy, which will provide optimization and trading services for battery storage assets in the UK wholesale market, as well as the Balancing Mechanism and ancillary services markets.

Up until now, that’s the sort of service that could only be supplied by fast-acting natural gas turbines. So as people charge their cars and drain electricity from the grid, the ability of the flow battery to reliably cycle dozens of times every day in response to power fluctuations will be invaluable.

Harper says that trends towards decentralized energy are boosting the prospects for flow batteries. As the need for EV charging infrastructure increases, along with the potential for disruption on distribution feeders, he thinks that the ability of flow batteries to regulate major fluctuating loads will become more valuable.

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