Batteries going with the flow

Australia is one of the fastest growing energy storage markets in the world with the most mature storage technologies being pumped hydro and lithium-ion batteries[i]. But other technologies have been developing in the background - such as flow batteries - which provide opportunities in larger scale applications.

It was recently reported that Australia’s chief scientist Alan Finkel, believes that flow batteries are potentially going to be a big contributor in grid-level stationary energy storage[ii]. Batteries can be used to provide back-up electricity if there is insufficient power generation to meet demand, and ensure the stability of the grid by helping to maintain a constant frequency.

Flow batteries, in particular, offer an opportunity to make renewable storage more affordable, and could help to grow the industry - increasing the prospects for utility-scale development of solar energy storage.

Flow batteries

Lithium-ion batteries are the most common rechargeable battery, used to deliver high power quickly from everyday household devices, electric vehicles to large grid-scale batteries. But they don't scale up well to the larger sizes needed to provide backup power for cities, according to Michael Perry, associate director for electrochemical energy systems, at United Technologies Research Center in East Hartford, Connecticut. However that is where flow batteries can provide opportunities in larger scale applications.

Scaling up the batteries to store more power simply requires bigger tanks of electrolytes. Vanadium has become a popular electrolyte component because the metal charges and discharges reliably for thousands of cycles. Rongke Power, in Dalian, China, for example, is building the world's largest vanadium flow battery, which should come online in 2020. The battery will store 800 megawatt-hours of energy, enough to power thousands of homes. The market for flow batteries - led by vanadium cells and zinc-bromine, another variety - could grow to nearly $1 billion annually over the next five years, according to the market research firm MarketsandMarkets.

The key difference between conventional and flow batteries is how energy is stored: Conventional batteries store energy as the electrode material, while a flow battery stores it as the electrolyte in flow cells.

Flow batteries rely on liquid electrolytes that are stored in external tanks, separated by a membrane, and pumped through electrochemical cells[iii]. They can almost instantly recharge by replacing the electrolyte liquid, while simultaneously recovering the spent material for re-energisation. Flow batteries can cycle more often and to greater depths of discharge at 100 per cent with no negative effects on the battery’s performance life (in comparison, lead-acid batteries have around 60 per cent depth-of-discharge, and lithium-ion batteries around 80 per cent.[iv])

While the focus to date has been on extending the lifespan of lithium-ion batteries, flow batteries can store power for four hours or more and last for decades (up to 25 years) before needing replacement, making them a promising prospect for powering large utility applications, micro-grids and off-grid projects.

Developing flow

Today, manufacturers offer a variety of flow battery chemistries with different cells being developed, such as redox, hybrid and membraneless: Redox batteries store energy in the liquid at all times. Hybrid flow batteries store at least some energy in solid metal during charge. While the liquids self-separate in one tank in a membraneless flow battery[v].

Generally, and depending on the chemistry, flow batteries tend to be less reactive, easy to dispose, are not prone to overheating, and are usually recyclable (helping to address question of what to do with batteries at the end of their performance life - previously looked at here).

Australia is a prominent country in the development of flow battery technology. Brisbane-based company, Redflow, has developed the world’s smallest zinc-bromine flow battery in commercial production. According to the company, their ZBM2 and ZCell flow batteries can shift energy in large volumes, and are designed to support applications ranging from telecommunications and renewables integration to on-grid and off grid remote power, microgrids and smart grids, and transmission and distribution deferral.

While Redflow’s ZCell is designed to provide energy storage at a smaller scale, such as homes or offices, their other product offering, the ZBM2, has 10kWh sustained energy storage capacity and can use 100 per cent of its energy storage capacity daily. The ZBM2 zinc-bromine flow battery is made from recycled or reused components, and at the end of its performance life the battery’s electrolyte solution can be purified and used for new batteries.

The company has signed a collaboration agreement with Chinese zinc-bromine flow battery company ZbestPower Co. to supply a large-scale (100kwh) Redflow battery energy storage solution for a demonstration project for a key smart grid project in China. While the company’s ZBM2 zinc-bromine flow batteries are now storing solar energy to provide a reliable power supply for a remote village in mountainous northern Thailand.

With technology born out of the University of New South Wales, VSUN Energy also offers Vanadium Redox Flow Batteries, which use a circulating electrolyte solution of vanadium pentoxide to store the charge in tanks.

VSUN states that energy storage capacity is expected to grow to 185 GWh over the next few years, and Vanadium Redox Flow Batteries want to capture 30 per cent of this market particularly in the large-scale commercial and grid-scale storage markets. According to the company, their flow batteries are suitable for storing large amounts of energy (particularly renewable energy) for later use, and are not prone to the thermal runaway known to occur with Li-ion batteries. A look at the US Department of Energy’s Global Energy Storage Database shows that Vanadium Redox Flow Batteries are involved in a wide number of projects.

Further development

But while Australia is leading the way in new flow battery technologies, commercialisation and costs remain challenging.

In 2017, Harvard researchers developed a new flow battery prototype that stores energy in organic molecules dissolved in neutral pH water. By modifying the structures of molecules, and making them water soluble, the researches were able to engineer a battery that loses only one per cent of its capacity every 1000 cycles.

Harvard reported lead researchers, Michael Aziz and Roy Gordon, as saying[vi]:

“Lithium ion batteries don’t even survive 1000 complete charge/discharge cycles,” said Aziz.

“Because we were able to dissolve the electrolytes in neutral water, this is a long-lasting battery that you could put in your basement,” said Gordon. “If it spilled on the floor, it wouldn’t eat the concrete and since the medium is noncorrosive, you can use cheaper materials to build the components of the batteries, like the tanks and pumps.”

The possibility of reduced costs and a clean solution presents a game changer – as a significant cost reduction could make stored wind and solar energy more competitive with energy produced from traditional power plants. The Harvard researchers are now working with several companies to scale up the technology for industrial applications. It will be an emerging technology to watch.

Below lists some major flow battery projects in Australia. For a complete list of all flow battery projects globally, visit the US Department of Energy Database which provides up-to-date information all storage developments: https://www.energystorageexchange.org/

• Monash University, Clayton Melbourne Vandadium Redox Flow Battery 300kW/1MWh. Announced
• Ergon Energy RedFlow Zinc Bromine Flow Battery 100kW/480kWh. Contracted. Demonstration project..
• UNSW – Gildemeister CellCube 30kW/130kWh. Operational
• UTS Sydney Zinc Bromine Flow Battery 25kW. Operational.
• King Island Expansion Vanadium Redox Flow Battery. 200kW.
• Global Change Institute M120. Brisbane. Zinc Bromine Flow Battery 120kW. Operational.
• RedFlow Adelaide. Base64Zinc Bromine Flow Battery 300kW

[i] https://www.chiefscientist.gov.au/wp-content/uploads/Energy-storage-paper.pdf

[ii] “Finkel backs unheralded Aussie battery tech companies to go global”, Australian Financial Review, 4 June 2019

[iii] https://www.chiefscientist.gov.au/wp-content/uploads/Energy-storage-paper.pdf

[iv] https://www.solarquotes.com.au/flowbatteries.html

[v] https://www.solarpowerworldonline.com/2017/12/what-is-a-flow-battery/

[vi] https://www.seas.harvard.edu/news/2017/02/long-lasting-flow-battery-could-run-for-more-than-decade-with-minimum-upkeep