Long time coming

First developed by NASA, flow batteries are a potential answer to storing solar – and wind – for eight to 10 hours, far beyond what is commonly achieved today with lithium-ion. In the first of a two-part special report, Andy Colthorpe learns what the flow battery industry faces in the fight for commercialisation.

Solar is easy to explain. Sunlight hits panels, electricity hits grid. Then come the inevitable questions about using power when the sun doesn’t hit the panels, about batteries and the well-rehearsed explanation comes that yes, while it would be great to use solar power 24/7, we’re just not there yet with the cost of technologies as they are, for the most part.

So the more complex explanation follows that lithium batteries are being deployed at large-scale to store energy for short periods of time, to deliver frequency regulation, or to remove specific hours of a peak demand period. A market need for long-duration storage remains elusive outside of specific circumstances such as remote grids where batteries and PV are replacing expensive diesel. Providers of flow batteries would beg to differ.

While acknowledging that lithium’s head start from a mass production perspective and other factors contribute to a higher capex overall for flow, flow energy storage providers are quick to point out the long lifetimes of their machines, the low cost of their raw materials, the comparative lack of fire hazard and associated balance-of-system costs and sheer ability to store huge amounts of energy, rather than power, mean flow could be the cost-effective long-duration choice of the renewables industry.

“People used to ask us what we needed the fifth hour for and now they ask if we can go to 10 hours,” Jorg Heinemann, chief commercial officer at Primus Power says.

Heinemann joined zinc bromine stationary energy storage maker Primus Power after eight years developing utility-scale PV with SunPower, believing long-duration storage to be the natural next step for renewable energy. Customers that have large amounts of solar PV are now approaching Primus with the intent to use solar-plus-storage as peaker replacements and to use behind-the-meter battery assets to offset transmission and distribution (T&D) investment costs.

“That’s beyond four hours [of storage], that means putting in a request for five, six or even eight hours, to take renewable power and add it to the storage and you’ve eliminated the need for a peaker. That last wave of use cases, T&D deferral, gas peaker replacement, heavy duty renewable extension,those are new, at least new to us. People have talked about them in theory, we’re now getting those active requests.

In California, where Primus is headquartered, lithium batteries have now been deployed to provide capacity in the wake of natural gas plant retirements and questions over security of supply following the Aliso Canyon gas leak, marking a milestone for batteries to be used on the grid for more than short-term balancing services. The state’s main investor-owned utilities now also have to include consideration of four-hour duration energy storage in their Resource Adequacy Plans. Other parts of the world are moving there faster, with various dispatchable solar projects announced in recent months.

Flow energy storage, which can use a variety of chemistries including vanadium, zinc bromine and in one instance, iron for the electrolyte, puts a central battery stack between electrolyte in tanks. As Navigant Research analyst Ian McClenny points out, the levelised cost of energy decreases as discharge duration increases. In other words: scale up the tank size, scale up the project’s energy need (as opposed to power), bring down the cost.

“The cost over the lifetime of the storage asset is heavily dependent on what type of applications the device will be serving,” McClenny adds, and although the capex required for flow might be higher than lithium, flow battery makers would argue that that initial cost is outweighed in the long run by the other benefits of ruggedness and long lifetime that they claim.

Navigant also sees flow energy storage as a four-hour+ duration storage device and the firm has identified flow batteries as one of the clean and distributed energy technologies expected to grow fastest in the next 10 years in terms of market share.

McClenny says at present the majority of advanced energy storage being deployed around the world is still providing services that require less than four hours’ duration.

“Consequently, Li-ion batteries can provide the same services that flow can at a lower capex,” within the context of most current global markets, McClenny says.

However, as Primus Power’s Jorg Heinemann argues, the planet is “heading toward close to free power during daylight hours” and the “base case that will eventually run the planet is to take renewable electricity, store it with long duration storage and dispatch it in the evening, night-time and early morning hours when the sun is not shining”.

Prices are falling and many utility-scale PV plants that are 10 years old today will be producing power almost for free in another 20 years, Heinemann cites as an indicator. “Now the typical solar developer or independent power producer is recognising energy storage as a very doable and economic thing, and a good value proposition.”

Jim Stover, business development VP at Pu Neng, soon to be rebranded VRB Energy in markets outside China, points out that that country’s renewable energy sector is about to put wheels in motion that could make flow unstoppable. Pu Neng, now US- and Canada-headquartered VRB’s subsidiary, is among the vanadium flow battery makers to be in the running for projects in China that will provide multiple hundreds of megawatt-hours of storage to local grids. China’s government set out its official stance on energy storage for the first time ever in October 2017 when it issued “Guiding Opinions on Promoting Energy Storage Technology and Industry Development”, the policy which informed the mammoth decision.

Already awarded is a contract for Rongke Power, which has a well-known subsidiary in the US, UniEnergy Technologies (UET), to install a 200MW/800MWh flow battery system in Dalian Province, with the company itself having emerged from the Dalian Institute of Chemical Physics originally.

The China National Energy Administration approved that project and is considering developers for a further 100MW / 500MWh system – for which Pu Neng is installing a 3MW / 12MWh demonstration project – and two further, reportedly 1GWh projects paired with wind energy and a nuclear plant. This would massively skew megawatt-hour deployment figures worldwide in flow’s favour, although the projects themselves are unlikely to be connected for at least another 10 years.

“The Chinese government I think in particular is happy to incentivise or call out vanadium like this. They want to push a number of technologies, but there is an awful lot of vanadium resources in China, both from mine sites and from steel slag recovery,” Jim Stover says.

“They’re trying to seize that as a good and natural fit, they don’t have a lot of lithium. They have a lot of lithium manufacturers but not a lot of lithium itself, or cobalt, or nickel even. That’s one of the dynamics in China.”

Big batteries, long durations, and (mostly) huge amounts of renewables enabled; the signs seem positive. Nonetheless, we have seen the likes of VIZN and Imergy hit the scene with numerous deployments and promising low cost storage, only to succumb to bankruptcy and layoffs. As Navigant’s Ian McClenny says, despite flow being his team’s forecasted “fastest growing electrochemical energy storage device over the next 10 years”, there are still “short term hurdles”.