by Julian Spector
March 14, 2019

Editor's note: This column serves as a companion to the earlier roundup of extant flow battery vendors. To complete the picture, we're turning this week to the non-flow technologies staking a claim on the grid storage market.

Lithium-ion owns the grid storage market now, but that might not always be the case.

The most numerous type of challenger to the mass-produced battery technology is the flow battery, which we profiled in January. But they're not the only ones taking on the quixotic quest to beat the most widely available, cost-effective product on the market.

This week, we'll check in on the rest of the challengers, which we might categorize as exotic or unconventional technologies, because they take such varied approaches to the task of storing electricity for long periods of time. This cohort includes gravity-based, compressed air, super-cooled gas and zinc-air storage. 

Crucially, they all have avoided bankruptcy, as peers like Aquion, LightSail and Alevo fell by the wayside. And if you're looking for thermal energy storage or flywheels, don't worry: we're just saving them for technology-specific coverage in the coming weeks.

Longer durations are coming

Why should we care about these iconoclasts, when lithium-ion just ended Q4 with 99.2 percent of the U.S. market, according to the Energy Storage Monitor?

Just as with energy storage more broadly, the current state of affairs matters far less than where things are going. One clear trend: The market keeps moving toward longer durations.

"Four years ago, we weren't even talking about 4-hour duration," said Mitalee Gupta, energy storage analyst at Wood Mackenzie Power & Renewables.

Now 4-hour systems are increasingly common, and forward-looking procurements are broaching longer discharge capacities. This trend is likely to continue, especially in regions with high penetrations of renewables, which are already facing curtailments during peak production times. But lithium-ion becomes less cost-effective at longer durations, which tends to be where the alternative technologies shine.

Lithium-ion's stunning cost reductions have proved the bane of companies pegging their success to beating that price point. Lithium-ion will continue to fall down the cost curve, but more slowly than in previous years, according to Gupta's analysis of battery supply chains. That means that unconventional storage companies shouldn't be caught off-guard the way some were in recent years.

As price becomes less of an obstacle, customers also may spend more time thinking about safety, in which nonflammable chemistries offer an advantage.

This won't be easy. The biggest hurdle is breaking past the pilot and securing the first large commercial order. Many of the companies on this list are still working on that. 

Some of them anticipate such large plants, once they reach scale, that even winning a few deals could propel them into positive cash flow.

"In 10 years, lithium is going to hold up its share, but we’ll start to see the other technologies come in," Gupta predicted. "Nothing beyond lithium-ion is making strong strides yet. But there is definitely room for other technologies to get in."

Here are the names that still stand a chance of success. We'll update the list as more arise.

Energy Vault

Headquarters: Lugano, Switzerland

Product: The Evie, which uses six smart cranes to raise and lower 35-ton blocks to charge and discharge electricity. The standard configuration delivers 4 megawatts/35 megawatt-hours of storage capacity.

Funding status: Raised two rounds. The amount remains undisclosed, but CEO Robert Piconi told GTM it was enough to cover initial customer deployments. 

Systems deployed: A one-seventh-scale pilot system in Switzerland. First full-scale deployment is slated for 2019, for Tata Power Company in India.


Headquarters: Edison, New Jersey

Product: The Aurora, which uses proprietary zinc hybrid cathode technology for four hours of energy storage. The company touts 100 percent depth of discharge and a nonflammable electrolyte. The website projects a 15-year product life (previously advertised as 30 years), but offers a one-year warranty.

Funding status: Global equipment supplier Holtec bought “a significant equity stake” in September 2018. Prior to that, Eos raised $23 million in October 2016, and the same amount in May 2015, after netting $27 million in two earlier rounds.

Systems deployed: Early prototypes for testing with various industrial partners. First commercial installation was a 250-kilowatt/1-megawatt-hour system for PSE&G in 2017; it serves a solar-powered microgrid at a wastewater treatment plant.

Highview Power

Headquarters: London, with U.S. base at the Urban Future Lab in Brooklyn

Product: Cryogenic/liquid air energy storage plants, using equipment from the conventional power and gas industries.

Funding status: Won £8 million grant from the U.K. government to fund the Manchester project (described below). The company had raised £17 million as of 2014.

Systems deployed: A 350-kilowatt/ 2.5-megawatt-hour pilot, followed by a 5-megawatt/15-megawatt-hour demonstration project in the Manchester area completed in 2018.


Headquarters: Toronto, Canada

Product: Hydrostatically compensated compressed air storage, that is, pumping air into a cavern with water in it to help maintain a constant pressure. Optimized for large capacity and long durations, but still operating at smaller scales.

Funding status: Raised about $25 million in equity, supplemented by government grants and revenue from the Ontario project.

Systems deployed: A small test facility in Toronto; commercial 2-megawatt unit plugged into Ontario's Independent Electricity System Operator. Next project, 5 megawatts, is slated for an abandoned mine in South Australia; expected online by mid-2020.

MGX Minerals

Headquarters: Vancouver, Canada

Product: Zinc-air batteries for long-duration storage. Formerly developed by ZincNyx Energy Solutions prior to acquisition in December 2017.

Funding status: Subsidiary MGX Renewables raised almost CAD $15 million to commercialize its technology, the company says.

Systems deployed: As of late 2018, the company was “ready to start commercialization.”


Headquarters: Scottsdale, Arizona

Product: Zinc-air batteries (formerly developed and sold by Fluidic). 

Funding status: $220 million raised before billionaire Patrick Soon-Shiong acquired the company. They don’t need to raise outside capital anymore.

Systems deployed: More than 3,000 zinc-air systems in nine countries, mostly in remote island or energy access markets like Indonesia and Latin America. Total installed capacity is close to 55 megawatt-hours.