Long-Duration Energy Storage

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Energy is stored in various forms. If it can be deployed for five hours or more, it is considered long-duration. Numerous technologies and products are under stages of development ranging from promising lab experiments to fully-realized commercial products available today. We prioritize stored energy for use in generating electricity, while recognizing that a limited number of industrial or heavy transport applications still require direct combustion.

This page is organized by type of energy storage. Within each category, we include links to company websites and related news.

Long-duration energy storage types include electrochemical, chemical, mechanical, and thermal.

Electrochemical Energy Storage


Ambri (Marlborough, MA); Liquid metal batteries: liquid calcium alloy anodes with a molten salt electrolyte and cathode made of solid antimony particles into stainless steel housing.

CellCube (Austria); Vanadium flow battery

Enlighten (Calgary, Alberta, Ca); Sodium and sulfur flow battery

ESS Inc (Wilsonville, OR); Iron flow battery

Eos Energy Storage (NJ and PA); Zinc-bromide flow battery

e-Zinc (Toronto, Ontario, Ca); Zinc-air flow battery

Form Energy (Somerville, MA); Iron-air battery

Redflow (Australia); Zinc-bromine flow battery

Zinc8 (Vancouver, British Columbia, Ca); Zinc-air flow battery

» Electrochemical Energy Storage News

» Form Energy selects West Virginia for its first iron-air battery plant
By Renewable Energy World
December 22, 2022

» Form Energy wins $450M to rust iron for multiday energy storage
The long-duration storage startup is on a fundraising tear as it validates its iron-air battery technology and scouts locations for a U.S. factory.
By Julian Spector, Canary Media
October 4, 2022

» ESS inks largest-ever US flow battery purchase with Sacramento utility
The innovative deal will supply 2 gigawatt-hours of storage over multiple years and includes provisions for workforce training in and around the California capital.
By Julian Spector, Canary Media
September 27, 2022

» ESS Inc ramps iron flow battery production capacity to 500MWh, signs 12GWh Australia deal
By Andy Colthorpe, Energy Storage News
August 12, 2022

» e-Zinc raises US$25m to begin commercial pilot production of long-duration storage
By Andy Colthorpe, Energy Storage News
April 7, 2022

» This iron and water battery could power a more renewable grid
By Jesse Nichols, Grist
February 10, 2022

» Form Energy announces partnership with Georgia Power to test 100-hour iron-air battery
By Jason Plautz, Utility Dive
February 10, 2022

» New York demonstration project to showcase potential of Zinc8’s long-duration zinc-air battery
By Jason Plautz, Utility Dive
January 26, 2022

» ROUNDUP: Long-duration energy storage news from CellCube, Malta, Gelion
By Andy Colthorpe,     Energy Storage News
December 6, 2021

» Zinc battery storage maker Eos gets US$25m deal to finance equipment
By Andy Colthorpe, Energy Storage News

By Andy Colthorpe, Energy Storage News

» Form Energy closes US$240 million funding round
By Andy Colthorpe, Energy Storage News

» Ambri gets US$144m investment and 13GWh materials deal for long-duration liquid metal batteries
By Andy Colthorpe, Energy Storage News

» Form Energy’s $20/kWh, 100-hour iron-air battery could be a ‘substantial breakthrough’
By Jason Plautz, Utility Dive
July 26, 2021

» Long-duration storage mystery revealed: Form Energy discloses details of ‘multi-day battery’ tech
By Andy Colthorpe, Energy Storage News
July 23, 2021

» Startup Claims Breakthrough in Long-Duration Batteries
Form Energy’s iron-air batteries could have big ramifications for storing electricity on the power grid
By Russell Gold, Wall Street Journal
July 22, 2021

» Why a seasoned energy executive sees a bright future in long-duration energy storage from ESS
Executive interview with Eric Dresselhuys, CEO of ESS Inc.
By Jennifer Runyon, Energy Storage World (sponsored content)
June 29, 2021

» ESS Inc’s all-iron flow battery will add long-duration storage to microgrid in Patagonia, Chile
By Andy Colthorpe, Energy Storage News
April 28, 2021

» Redflow supplying 2MWh of zinc-bromine flow batteries to California bioenergy plant
By Andy Colthorpe, Energy Storage News

» ‘All-iron’ flow battery maker ESS Inc launches ‘configurable’ megawatt-scale product
By Andy Colthorpe, Energy Storage News
February 15, 2021

» Can a Novel Zinc Battery Deliver Clean Multiday Backup Power?
California is testing Canadian startup e-Zinc’s long-duration technology to keep businesses powered through wildfires and outages.
By Julian Spector, GreenTech Media
September 18, 2020

» Iron Flow Battery Startup ESS Raises $30M From SoftBank and Breakthrough
The flow battery survivor marks the latest in a series of recent investments in unconventional long-duration storage technologies.
By Julian Spector, Green Tech Media
October 29, 2019

Chemical Energy Storage

Green hydrogen, etc. stored as compressed gas, liquid, or solid

Ceres Power (UK); Fuel cell

Plasma Kinetics (Scottsdale, AZ); Solid hydrogen storage at room temperature

» Chemical Energy Storage News

» Energy Storage Breakthrough – Solid Hydrogen Explained
Undecided with Matt Ferrell, YouTube
Nov 9, 2021

» Plasma Kinetics May Revolutionize Hydrogen Storage For EVs
By Gustavo Henrique Ruffo, Auto Evolution
August 13, 2021

Mechanical Energy Storage

Pumped hydro-power, suspended solid mass, flywheels, gas in compression or phase change, etc.

Augwind (Israel); Combination of pumped hydro and compressed air energy storage in underground tanks.

Energy Dome (Italy); CO2 phase change battery

Energy Vault (Westlake Village, CA); Suspended solid blocks

Highview Power (UK); Liquid air

Hydrostor (CA); Compressed air

Revterra (Houston, TX); Flywheel

Quidnet Energy (Houston, TX); Pressurized water in underground rock formations – variation on pumped hydro-power.

» The world’s first CO2 battery for long-duration energy storage is headed to the US
By Michelle Lewis, Electrek
November 14, 2022

» Mechanical Energy Storage News

» We Can Store Our Excess Renewable Energy In An Energy Vault
The company, Energy Vault, has commercialized the ultimate energy storage technology that will build the foundation of a clean energy future – brick by brick.
By James Conca, Forbes
January 27, 2022

» Hydrostor secures $250 million from Goldman Sachs amid rising investor interest in long-duration storage
By Jason Plautz, Utility Dive
January 12, 2022

» Korea Zinc agrees to invest US$50m in gravity storage startup Energy Vault ahead of NYSE listing
By Andy Colthorpe, Energy Storage News
January 6, 2022

» Liquid air tech assessed in China for ability to address ‘critical need’ for long-duration energy storage
By Andy Colthorpe, Energy Storage News
January 6, 2022

» Gravity Could Solve Clean Energy’s One Major Drawback
Finding green energy when the winds are calm and the skies are cloudy has been a challenge. Storing it in giant concrete blocks could be the answer.
By Matt Reynolds, Wired
January 4, 2022

» IEC inks $8 million deal with company that uses air, water to store energy
Touted as a cost-competitive, sustainable alternative to lithium batteries, Augwind’s ‘air batteries’ can power turbines when needed
By Sue Surkes, The Times of Israel
December 15, 2021

» Hydrostor plans 4 GWh long-duration storage project in Southern California
By Kavya Balaraman, Utility Dive
December 2, 2021

» ‘CO2 battery’ technology getting megawatt-scale demonstrator in Italy
By Andy Colthorpe, Energy Storage News
May 27, 2021

» Flywheels Turn Superconducting to Reinvigorate Grid Storage Potential
Energy losses defeated previous-gen flywheels as viable big batteries; so new ones levitate more efficiently
By Karen Kwon, IEEE Spectrum
April 7, 2021

» To batteries and beyond: Compressed air, liquid air and the holy grail of long-duration storage
Proponents of the technologies are looking to carve out a niche for themselves in the market. In both cases, a key draw is duration.
By Kavya Balaraman, Utility Dive
October 14, 2020

» Climate emission killer: construction begins on world’s biggest liquid air battery
By Damian Carrington, The Guardian
June 18, 2020

Thermal Energy Storage

Molten salt, etc.

Azelio (Sweden); Aluminum alloy phase change

Echogen Power (Akron, OH); Unspecified thermal storage for electricity production

Malta Inc (Cambridge, MA); Pumped thermal storage

Rondo Energy, Inc (San Francisco Bay Area, CA); High temp energy storage for industrial processes.

Stiesdal (Denmark); Pumped thermal storage with crushed rock

» Can thermal storage fire up the net-zero transition?
After almost a decade in incubation, thermal energy storage is finally coming of age to play its long-fated role in the net-zero transition.
By Oliver Gordon, Energy Monitor
August 8, 2022

» Thermal Energy Storage News

» Renewable energy heat batteries for industrial applications gain funding
Startup Rondo Energy closed a $22 million Series A funding round to decarbonize industrial processes with equipment that converts solar and wind energy into thermal energy.
By Ryan Kennedy, PV Magazine
February 8, 2022

» NREL Results Support Cheap Long Duration Energy Storage in Hot Sand
By Susan Kraemer, SolarPACES
February 8, 2022

» Long-duration energy storage startups Energy Vault, Malta Inc in 2.6GWh deployment discussions
By Andy Colthorpe, Energy Storage News

» Long-duration thermal energy storage startup Azelio wins first commercial order
By Andy Colthorpe, Energy Storage News

» Challenges of financing and low renewables still plague energy storage in emerging markets
By Molly Lempriere, Energy Storage News