The Energy Storage Report 2024

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‘Ultra-high throughput, twice daily cycling and 24/7 renewables’: Flow battery providers talk up advantages


Flow battery companies at the RE+ 2023 show in Las Vegas offered takes on how their technologies can compete in the evolving energy storage market.

ESS Inc, the US-headquartered manufacturer with a proprietary flow battery chemistry based on an iron and saltwater electrolyte, revealed during the clean energy trade event yesterday that the first units in its potential 200MW/2,000MWh partnership with Sacramento Municipal Utility District (SMUD) have been commissioned.

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Thought to represent an initial installation of around 225kW/3,000kWh across six of the company’s Energy Warehouse flow battery units, they mark a milestone in the partnership which ESS Inc first announced this time last year at RE+ 2022.

“At ESS, we’re proud to be delivering the long-duration energy storage solutions that our customers need to achieve their clean energy goals,” CEO Eric Dresselhuys told

SMUD is among the more progressive utilities in the US when it comes to decarbonisation, targeting emissions-free electricity supply to all its customers by 2030. ESS Inc senior VP of sales and business development Hugh McDermott had said last year that the partnership enabled SMUD to “de-risk” some of that journey.

While that initial deployment is small relative to the total pipeline ESS Inc and SMUD could eventually work on, the idea behind that is that the technology provider and the utility will explore that scale-up together.

“The commissioning of our first systems delivered to SMUD is a significant milestone in that partnership and we look forward to working with them to support their ambitious 2030 Clean Energy Vision,” Dresselhuys told yesterday.

Partnerships between long-duration energy storage (LDES) providers and forward-thinking utility customers help “push the momentum and bring the reality of what’s truly needed,” in the energy transition, Julia Souder, CEO of the Long Duration Energy Storage Council (LDES Council) trade group told at the show.

“Being able to demonstrate that they’re de-risking the transition by bringing LDES in is, I think, a huge success,” Souder said, particularly because of that scope to scale up projects in number and size, while the flow battery provider has also committed to helping train and educate SMUD workers in how to work with flow batteries and related tech.  

‘Near 24/7 renewables’

Meanwhile, representatives from two other flow battery manufacturers, Redflow and Invinity, offered their thoughts on how competitive flow batteries are today, and what needs to happen for them to become a mainstream option in planning for the low carbon grid of the future.

Speaking in a session hosted by LDES Council, Jan Petrenko, Invinity Energy Systems sales manager for North America spoke about some of the vanadium redox flow battery (VRFB) provider’s recent and ongoing projects.

One is Chappice Lake Solar + Storage, in Alberta, Canada, at which a 21MWp ground mount solar PV array is being paired with a 2.8MW/8.4MWh VRFB for developer Elemental Energy.

Supported by funding from provincial agency Emissions Reduction Alberta, the flow battery system will “turn standard solar PV” into a 24/7 dispatchable asset, while participating in Alberta’s operating reserve market and its wholesale electricity market, which is somewhat similar to Texas’ ERCOT, Petrenko said.

The battery system, which is now onsite and readying for commissioning, will cycle twice daily, for four hours at a time. The system also needs to stand up to Alberta’s cold weather challenge, with average January temperatures ranging between -2°C (35.6°F) and -11°C. Invinity’s V3 model VRFB’s ambient operating temperature range is between -5°C and 45°C, capable of coping with those conditions, the representative claimed.

The project will be an opportunity to demonstrate the operational advantages of the technology, from its safety profile – the batteries do not go into thermal runaway under abuse conditions – to the use of sustainable and abundant materials, to a longer lifetime with up to 25 years of “constant cycling” possible.

The higher upfront costs of flow batteries versus lithium-ion are more than offset by the lifetime economics that manufacturers like Invinity claim are much better.

VRFBs’ capability of performing “unlimited cycling” and an “ultra-high throughput” over their lifetime mean that the levelised cost of storage (LCOS) can be lower than a lithium battery energy storage system (BESS) performing similar applications, Jan Petrenko claimed.

Redflow’s Mark Higgins spoke about the company’s two megawatt-hour scale California projects, one already completed over a year ago at 2MWh and one now under construction which will be 20MWh when completed.

The 20MWh project, about which interviewed Redflow CEO Tim Harris a few months ago, will also bring the customer, California’s Paskenta Tribe, to operate a community microgrid at “very close to 24/7 renewable energy,” Higgins, president and chief commercial officer for North America at Redflow said.

Building up scale, bridging the market gap

Redflow again has a different battery chemistry to ESS Inc and Redflow, using zinc bromine electrolyte in its systems. However, what all three have in common is that each has gradually scaled up the size of projects that it works on in recent years.

Redflow is headquartered in Queensland, Australia, and in its home country began with large residential systems, many of which were off-grid in rural areas, as well as other distributed and remote applications like telecoms towers in Australia and elsewhere. However, in North America, Redflow is targeting only megawatt-hour scale projects, Higgins said.

Similarly, Anglo-American VRFB provider Invinity started out small, but as Invinity VP of business development Matthew Walz mentioned in an interview with earlier this year, has graduated up to discussions about projects in the range of 30MWh – 50MWh and is targeting “triple-digit MWh” projects from 2025 onwards.

Each of the two companies’ larger projects have required a degree of funding support, largely from government bodies, but their awards from authorities show that the technology is capable of them.

At the same time, Redflow’s Mark Higgins praised the California Energy Commission – which has financially supported projects including its 20MWh installation as well as flow batteries and other long-duration tech from other providers – for stepping in to incentivise projects that otherwise couldn’t make revenues in market structures that aren’t yet ready to incorporate long-duration storage.

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