by Julian Spector
January 25, 2019

It’s a tough and thankless job, trying to replace the undisputed energy storage market leader.

Yet that’s what dozens of companies have dedicated themselves to by developing flow batteries, the most numerous of the newfangled electrochemical storage alternatives to lithium-ion batteries.

Flow batteries circulate liquid electrolytes to store and discharge electricity (see Eric Wesoff's thorough explanation for Squared readers here). They promise longer lifetimes and heavier cycling capabilities than lithium-ion. Yet lithium-ion, boosted by electric-vehicle manufacturing supply chains, has surged to a U.S. market share greater than 90 percent for the last several years.

"Every flow battery company has been talking about how flow batteries are great for long-duration solutions and can beat lithium-ion," said Brett Simon, energy storage analyst for Wood Mackenzie Power & Renewables. "They're still trying to put a stake in the ground."

After years, and in some cases decades, flow batteries have barely established a foothold in the grid storage market, but at least some of them refuse to die. In this week’s Storage Plus, we’ve compiled a comprehensive guide to the U.S. flow battery vendor landscape, which will be updated as new entrants come to our attention.

Use this as a reference when you’re trying to remember which companies haven’t gone bankrupt yet, who loves vanadium and who trash-talks it, and where any installed units are operating. It turns out that last one is harder to track down than you might expect.


Headquarters: Wilsonville, Ore. 

Product: The Energy Warehouse, a containerized iron flow battery that can be shipped dry and filled with water onsite.

Funding status: Raised $13 million Series B in December 2017 led by chemical conglomerate BASF. The funding was targeted for manufacturing upgrades to achieve an annual production capacity of 900 megawatt-hours.

Systems deployed: Two 30-kilowatt/110-kilowatt-hour systems installed at Fort Leonard Wood in a military microgrid test site. A 50 kilowatt/ 400 kilowatt-hour system at the UCSD microgrid and at the DNV GL/Group NIRE Wind Facility in Lubbock, Texas. 10 kilowatt/ 65 kilowatt-hour system at Stone Edge Farm Microgrid. Two orders to BASF in Germany; one contract for a Pacto Energy subsidiary in Brazil.

EnSync (formerly known as ZBB)

Headquarters: Menomonee Falls, Wisc.

Product: Agile Flow Battery, a modular zinc-bromide system built for commercial and industrial use with 55 kilowatt-hours of energy capacity.

Funding status: Publicly traded on the New York Stock Exchange, for now, as ESNC. Peaked shortly after IPO in 2007 at nearly $30 per share. Has since fallen to 20 cents per share, prompting the NYSE to send a “deficiency letter.” EnSync must show improvement by July 7 or face delisting.

Systems deployed: The company confirmed it had installed multiple Agile systems in its Hawaii projects, but did not provide further details in time for publication.

Lockheed Martin Energy

Headquarters: Grand Prairie, Texas

Product: GridStar flow battery system, which uses “proprietary battery chemistry comprising metal ligand coordination compounds.” Lockheed acquired MIT spinoff Sun Catalytix in 2014, and has developed its technology into a commercial product in the years since.

Funding status: Part of a publicly traded defense and aerospace contractor with market cap north of $80 billion.

Systems deployed: Prototypes operating at a facility in Massachusetts. An executive told Reuters in April 2018 that the product would come in a “little more than a year.”

Primus Power

Headquarters: Hayward, California

Product: Energy Pod 2, featuring zinc bromide in a single tank with titanium electrodes and no membrane needed. Modular units contain 25 kilowatts/125 kilowatt-hours.

Funding status: Raised $32 million round in 2017, bringing total equity funding to $94 million.

Systems deployed: At Beijing campus of Goldwind’s microgrid subsidiary, Puget Sound Energy, Marine Corps Air Station Miramar, and elsewhere. As of last fall, Primus was working through a “firm order book” of roughly 7 megawatts.

Storion (spun out from ITN)

Headquarters: Littleton, Colo.

Product: Vanadium flow battery

Funding status: Raised “more than $40 million in research and development through 20 years of innovation,” including grants from ARPA-E. Strategy is to find local partner with big balance sheet in new markets, to overcome bankability challenge.

Systems deployed: The first commercial installation is underway in Germany through a joint venture, should be online by the end of February to perform two cycles a day of renewables shifting. Another is headed for an Xcel Energy test site near Denver.


Headquarters: Mukilteo, Wash.

Product: ReFlex, an “advanced vanadium flow battery,” based on an electrolyte licensed from the Department of Energy's Pacific Northwest National Laboratory. 

Funding status: Raised $25 million Series B in late 2015.

Systems deployed: Installed a 100-kilowatt/400-kilowatt-hour system as part of a smart grid pilot in Chattanooga, Tenn. Demo project at Natural Energy Laboratory of Hawaii Authority technology park. Demo at hospital in the Bronx aimed at grid resilience.

Vionx Energy

Headquarters: Woburn, Mass.

Product: Vanadium flow based on stack design developed by United Technologies Corporation,

Funding status: Raised $26 million in 2018, adding to previous venture capital financing of at least $79 million. Enhanced bankability by creating a performance insurance policy backed by New Energy Risk.

Systems deployed: Ft. Devens microgrid demo. Two projects with National Grid, both 500 kilowatts/3 megawatt-hours, demonstrating wind integration and solar integration. Helpfully listed on company website.

ViZn Energy

Headquarters: Columbia Falls, Mont.

Product: Containerized zinc-iron flow batteries in a range of sizes.

Funding status: Temporarily halted operations in 2018 after a funder pulled out. Secured $15 million round in June to resume operations. Recently finalized a deal to supply flow batteries to an industrial consortium in the China market.

Systems deployed: Pilot system runs at Idaho National Laboratory and a commercial system is operational at a resort microgrid in Nicaragua. Expected to ship pilot systems to partners in Europe and China and launch commercial units later in 2019.