Energy Storage Systems Inc, publicly traded as ESS Tech Inc (NYSE: GWH), is an American manufacturer of iron flow battery technology for long-duration energy storage applications. Founded in 2011 by Craig Evans and Julia Song, the company specializes in producing batteries that store energy for 4 to 12 hours using earth-abundant materials like iron, salt, and water.
Company Overview and Core Technology
Energy Storage Systems Inc operates from its headquarters in Wilsonville, Oregon, where it designs and manufactures iron flow batteries specifically engineered for commercial and utility-scale energy storage. The company's technology differs fundamentally from conventional lithium-ion batteries by separating power generation from energy storage capacity, allowing for independent scalability of each component.
The iron flow battery system works by circulating liquid electrolytes through electrodes to charge and discharge electrons. Unlike lithium-ion batteries that degrade over time, Energy Storage Systems Inc's iron flow technology maintains its full capacity throughout its 25-year design life with unlimited cycling capability. This longevity translates to significant cost advantages for utilities and commercial customers seeking reliable backup power or renewable energy integration.
As of 2024, Energy Storage Systems Inc reported annual revenues of $6.3 million, though the company has faced financial challenges common to emerging clean energy technology firms. The long-duration energy storage market itself was valued at approximately $4.84 billion in 2024 and is projected to reach $10.43 billion by 2030, growing at a compound annual growth rate of 13.6%.
Product Portfolio
Energy Storage Systems Inc offers three main product lines designed for different scales of deployment:
Energy Warehouse serves as the company's commercial and industrial solution, providing behind-the-meter energy storage for facilities requiring 4 to 12 hours of backup power. These systems typically range from 50 kW to 90 kW with capacities up to 600 kWh. The Energy Warehouse has seen deployment at various sites including the Sacramento Municipal Utility District, where six systems began operation in 2022.
Energy Center targets utility-scale applications, offering front-of-the-meter storage with flexible configurations to meet grid-scale requirements. These systems can be connected in parallel to support projects ranging from sub-megawatt to tens-of-megawatt scale. Portland General Electric received the first Energy Center systems for commissioning in 2024.
Energy Base represents the company's newest product line, introduced in late 2024 as part of a strategic pivot toward gigawatt-scale storage projects. This modular architecture enables storage duration extension from 12 to 22 hours with lower costs and improved operational flexibility, specifically targeting data centers and large-scale renewable energy operators.
Iron Flow Battery Technology Explained
The core innovation behind Energy Storage Systems Inc lies in its iron-based redox flow battery chemistry. The system employs iron chloride electrolytes in two separate tanks, with ions exchanged through a membrane while liquids circulate in their respective compartments. During charging, electrical energy converts iron from one oxidation state to another, storing the energy chemically. During discharge, the process reverses to release electricity.
This chemistry offers several practical advantages. Iron costs approximately $2 per kilogram and is abundantly available as a byproduct of steel production. The electrolyte solution is non-flammable, non-toxic, and stable at room temperature with neutral pH. Testing has demonstrated that Energy Storage Systems Inc's batteries can maintain 98.7% of maximum capacity over 1,000 consecutive charging cycles, with potential for over 20,000 cycles throughout the system's lifetime.
The technology performs reliably across temperature ranges where other battery chemistries fail. While vanadium redox flow batteries precipitate toxic compounds above 40°C, and lithium-ion batteries require active cooling systems, iron flow batteries actually benefit from higher operating temperatures without requiring thermal management infrastructure.
Market Position and Applications
Energy Storage Systems Inc competes in the rapidly expanding long-duration energy storage sector, which addresses a critical gap in renewable energy integration. Solar and wind power generation fluctuates based on weather conditions, creating supply-demand imbalances that require storage solutions capable of dispatching energy for extended periods when renewable sources aren't producing.
The company's systems serve multiple use cases. Grid operators deploy them for frequency regulation and voltage support, absorbing excess energy during low-demand periods and releasing it during peak consumption. Commercial customers use Energy Storage Systems Inc batteries for demand charge reduction, storing electricity when rates are low and discharging during expensive peak periods to lower overall energy costs by up to 33%.
Microgrid applications represent another growing segment. The U.S. Army Corps of Engineers installed an Energy Warehouse system at Fort Leonard Wood, Missouri, integrating it into a tactical microgrid designed to reduce fuel consumption at contingency bases. Similarly, Schiphol Airport in Amsterdam deployed the first iron flow battery at a major airport facility, using it to recharge electric ground power units as part of the airport's sustainability strategy.
Recent Deployments and Partnerships
Energy Storage Systems Inc has secured several significant contracts demonstrating commercial traction. The Sacramento Municipal Utility District agreement, announced in 2022, involves deployment of up to 200 megawatts and 2 gigawatt-hours of storage capacity. Once fully operational, this installation is expected to eliminate approximately 284,000 metric tons of CO2 emissions annually from SMUD's electrical system.
In Germany, utility company LEAG contracted with Energy Storage Systems Inc for a 50 MW / 500 MWh system as part of its transition away from coal power. This project, when completed, will become one of Europe's largest flow battery installations and is expected to displace 50,000 tons of coal consumption daily while eliminating 20 million tons of CO2 annually.
California utilities have been particularly active adopters. Burbank Water and Power commissioned a 75 kW / 500 kWh system paired with a 265 kW solar array in 2024, powering approximately 300 homes. The Turlock Irrigation District integrated an Energy Warehouse into Project Nexus, which combines solar panels installed over irrigation canals to simultaneously generate clean energy and reduce water evaporation.
Tampa Electric ordered multiple Energy Center systems for delivery in 2024, representing the company's first commercial shipments of its utility-scale product line to a major investor-owned utility in Florida.
Financial Performance and Challenges
Energy Storage Systems Inc went public through a SPAC merger and began trading on the New York Stock Exchange under ticker GWH. The company reported Q2 2025 revenue of $2.4 million, representing 578% year-over-year growth, though still reflecting the challenges of scaling a capital-intensive manufacturing operation.
The company has worked to reduce costs throughout its supply chain. Production costs for Energy Warehouse systems decreased by 40% during 2024, while commissioning time was cut in half through improved installation processes. Energy density improved by 25% through enhanced electrolyte chemistry, allowing more energy storage in the same physical footprint.
To fund expansion, Energy Storage Systems Inc secured financing agreements including up to $50 million from the Export-Import Bank of the United States to support manufacturing capacity growth. The company expects to draw down approximately $10 million from this facility to fund production infrastructure through 2026.
Despite technological progress, the company has faced liquidity concerns common to emerging technology companies in capital-intensive industries. Leadership implemented operational resets in 2024 and 2025, pivoting strategy toward the higher-capacity Energy Base product line while discontinuing legacy products to focus resources on larger-scale projects with better unit economics.
Competitive Landscape
Energy Storage Systems Inc operates in a market with both established players and emerging competitors. Form Energy develops iron-air batteries claiming up to 100 hours of storage duration. Eos Energy Enterprises manufactures zinc-based batteries for 3 to 12-hour applications. Traditional vanadium redox flow battery manufacturers include companies like Sumitomo Electric Industries and Invinity Energy Systems.
The competitive advantages Energy Storage Systems Inc emphasizes include its use of non-toxic, earth-abundant materials that avoid supply chain risks associated with lithium, cobalt, or vanadium. The company's American manufacturing base positions it to benefit from domestic content requirements in the Inflation Reduction Act and Foreign Entity of Concern provisions that favor U.S.-made energy storage systems.
However, Energy Storage Systems Inc faces significant competition from lithium-ion battery manufacturers that benefit from massive production scale and declining costs. While lithium-ion systems typically provide only 2 to 4 hours of storage, their lower upfront costs make them attractive for many applications where long duration isn't required.
Industry Trends and Growth Drivers
Several macroeconomic trends support demand for long-duration energy storage technologies. Global renewable energy investments reached $2 trillion in 2024 according to the International Energy Agency, with solar and wind capacity additions accelerating worldwide. This renewable growth creates increasing need for storage solutions to manage intermittency and ensure grid reliability.
Data center electricity demand is projected to increase 165% by 2030, driven largely by artificial intelligence computing workloads. These facilities require extremely reliable power with minimal downtime, creating opportunities for long-duration backup power systems. Energy Storage Systems Inc has positioned its Energy Base product line specifically to address this emerging market segment.
Decarbonization mandates are pushing utilities to retire fossil fuel peaker plants that traditionally provided grid flexibility. Storage systems capable of dispatching power for 8 to 12 hours can economically replace these natural gas facilities in many applications, particularly when paired with renewable generation assets.
North America represented the largest regional market for long-duration energy storage in 2024, valued at $1.17 billion, with strong growth projected through 2030. Government incentives, including production tax credits and investment tax credits under the Inflation Reduction Act, provide financial support for storage deployments.
Safety and Environmental Profile
Iron flow batteries offer inherent safety advantages over other electrochemical storage technologies. The electrolyte solution is water-based and operates at neutral pH, eliminating risks of thermal runaway or fire that concern lithium-ion installations. There are no toxic fumes or explosive reactions possible with iron, salt, and water chemistries.
A lifecycle analysis performed by UC Irvine comparing Energy Storage Systems Inc's technology to vanadium redox flow batteries, zinc bromine flow batteries, and lithium-ion systems found iron flow batteries had the lowest global warming potential across manufacturing, use, and end-of-life phases. Iron-based systems produced 67% less greenhouse gas emissions compared to lithium-ion equivalents.
The environmental advantages extend to raw material extraction. Iron is a byproduct of existing steel manufacturing, requiring no additional mining operations. Salt is similarly abundant and extracted through established processes with minimal environmental impact. This contrasts with lithium, cobalt, and vanadium mining, which involves more intensive extraction processes and geopolitical supply chain risks.
Frequently Asked Questions
How long can ESS batteries store energy?
Energy Storage Systems Inc's current products provide 4 to 12 hours of continuous energy discharge, with the new Energy Base line extending this to 22 hours. Duration depends on system configuration and can be scaled by increasing electrolyte tank volume without changing the power stack.
What maintenance do iron flow batteries require?
The systems require periodic maintenance of pumps, valves, and control systems, similar to other industrial equipment. The electrolyte solution may need rebalancing over time using a proton pump integrated into the system design. However, the batteries don't experience capacity degradation, eliminating the need for module replacements common with lithium-ion systems.
Where are ESS batteries manufactured?
Energy Storage Systems Inc manufactures its products in Wilsonville, Oregon, using a predominantly American supply chain. The company has invested in automated production lines capable of producing over 600 MWh annually per line, with plans for continued capacity expansion.
How do ESS batteries compare to lithium-ion on cost?
Initial capital costs per kilowatt-hour tend to be higher for iron flow systems compared to lithium-ion. However, the 25-year design life with no capacity degradation results in lower levelized cost of storage over the system lifetime. Energy Storage Systems Inc targets achieving $0.05 per kWh to meet Department of Energy cost goals by 2030.
The iron flow battery technology developed by Energy Storage Systems Inc represents one approach to solving the long-duration energy storage challenge facing the renewable energy transition. With projects deployed across the United States and expanding internationally, the company is working to prove that earth-abundant materials can provide reliable, safe energy storage at scale. The coming years will determine whether this technology achieves the commercial success necessary to become a significant player in the rapidly evolving energy storage landscape.
Key Data Sources:
ESS Tech Inc. Investor Relations and Financial Reports (2024-2025)
Long Duration Energy Storage Market Analysis, MarketsandMarkets (2024)
Wikipedia: Iron Redox Flow Battery (October 2025)
MIT Technology Review: Grid Storage Article (June 2022)
Pacific Northwest National Laboratory Research Publications (March 2024)
Energy-Storage.news Industry Coverage (2024-2025)