A new white paper from Elestor suggests its hydrogen–iron flow battery architecture may offer a durable and cost-effective solution for grid-scale energy storage, with testing indicating operational lifetimes of up to 25 years.
The study evaluates the technology under continuous, commercially relevant conditions, examining how the system performs over extended cycling periods.
According to the company, results suggest the design can maintain stable efficiency and performance across tens of thousands of charge–discharge cycles, while avoiding many of the material supply constraints associated with other battery chemistries.
Long-duration storage challenge
Energy storage systems intended for grid applications must meet stringent requirements. They need to operate for decades, cycle frequently without major degradation, and remain economically competitive.
Many battery technologies show promising results in laboratory settings but have limited long-term data from realistic operating environments. Elestor’s research aims to address that gap by testing a large-format prototype designed around the same principles as a commercial system.
The company’s hydrogen–iron flow battery uses hydrogen gas and dissolved iron salts as the active materials in an electrochemical process that converts chemical energy into electricity and back again.
Unlike conventional batteries, which store both power and energy in the same cells, flow batteries separate those functions.
In this architecture, the power output is determined by the electrochemical stack, while the energy storage capacity depends on the size of the electrolyte tanks. That separation allows the system’s capacity to be scaled more flexibly for different storage durations.
Common materials, scalable design
A key feature of the hydrogen–iron chemistry is its reliance on relatively abundant materials. Hydrogen is used at the anode, while the cathode reaction involves a reversible redox process between ferric and ferrous iron ions in solution.
Because the electrolyte is water-based and relies on widely available elements, the company argues the design avoids many of the supply-chain risks associated with metals such as lithium, cobalt, or vanadium.
However, the study stresses that low-cost materials alone are not enough to make a storage technology commercially viable.
For long-duration applications, durability becomes one of the largest drivers of total system cost. If equipment must be replaced frequently, the economics of storage quickly deteriorate.
Testing under realistic conditions
To evaluate durability, researchers operated a large-format cell stack with an active surface area comparable to deployable commercial units.
The system includes a hydrogen-fed anode, a proton-conducting membrane, and a carbon-based cathode designed to support iron redox reactions efficiently.
The electrolyte – an acidic aqueous iron salt solution – was circulated continuously through the system. Testing took place at elevated temperatures and constant current densities, conditions intended to mirror real industrial operation.
Throughout the trial period, the battery was automatically monitored through industrial control systems that logged electrochemical and operational data.
Stable efficiency over thousands of cycles
The validation campaign involved continuous operation across tens of thousands of charge–discharge cycles. Over that period, the hydrogen–iron flow battery maintained energy efficiency levels above the minimum targets typically required for commercial deployment.
According to the report, the system achieved energy efficiency above 80% and round-trip efficiency exceeding 75% at the system level. Importantly, the electrochemical core maintained stable performance throughout the test period, with no evidence of structural degradation.
Periodic conditioning procedures were used to restore the system to its optimal performance window. These maintenance steps, which involve controlled operational adjustments rather than hardware changes, are described as routine practices compatible with industrial energy systems.
Researchers also observed that short rest periods could reduce internal resistance within the cell, suggesting the materials undergo reversible equilibration during operation.
Resilience to operational interruptions
Real-world energy infrastructure must cope with unexpected events, including shutdowns or power interruptions. During the validation programme, the system experienced several external disruptions unrelated to the battery itself.
In each case, the system was restarted without negative effects on the electrochemical components or long-term performance. The company says this resilience demonstrates the inherent chemical stability of the hydrogen–iron flow battery approach.
Projected multi-decade lifetime
Based on the observed stability during extended testing, the study projects that systems using the technology could operate for 20 to 25 years in grid-scale applications.
The lifetime estimate is derived from measured performance trends rather than assumptions about future improvements or new materials. When adjusted to typical annual cycling profiles for grid storage, the data indicate the technology could support multi-decade deployment.
Such longevity could significantly affect the economics of large-scale storage. Longer lifetimes reduce replacement costs and spread capital investment across more years of operation.
Implications for storage costs
Elestor argues that combining durable performance with low-cost materials could allow the hydrogen–iron flow battery to achieve competitive economics for long-duration energy storage.
The company estimates that the technology could reach capital expenditure levels around €15 per kilowatt-hour, with a levelised cost of storage near €0.02 per kilowatt-hour over the system lifetime.
While these figures depend on large-scale deployment and manufacturing, they highlight the potential economic advantages of the chemistry.
A contender for long-duration storage
As electricity systems integrate higher shares of renewable power, technologies capable of storing energy for many hours or even days are becoming increasingly important.
The results presented in Elestor’s white paper suggest that the hydrogen-iron flow battery could offer a durable and scalable option for long-duration storage.
If the technology performs similarly in full commercial installations, it may help provide the kind of long-lived infrastructure needed to support a low-carbon power grid.
