en.Wedoany.com Reported - The 322 MW onshore wind farm Windpark Zeewolde in the Dutch province of Flevoland, one of the largest of its kind in Europe, has partnered with Dutch energy storage developer Elestor to deploy a 20 MW hydrogen-iron flow battery system. With an energy storage capacity ranging from 200 to 800 MWh and a duration window set between 10 and 40 hours, the system is primarily designed for overnight storage and multi-day wind lulls. In contrast, most utility-scale lithium-ion batteries currently deployed operate for only 2 to 4 hours, occasionally extending to 6 or 8 hours. This project aims to address the gap in commercial large-scale application of long-duration energy storage.
Elestor's hydrogen-iron flow battery operates on a principle different from traditional lithium-ion batteries. During charging, electricity splits water to produce hydrogen, which then reacts with an iron-based electrolyte; during discharging, the reverse reaction sends electricity back to the grid. Since energy is stored in liquid electrolyte within external tanks rather than inside the battery cells, extending storage duration primarily relies on increasing tank volume rather than adding more costly battery stacks. Elestor states that the technology can achieve durations of 8 to 150 hours, and this deployment will be calibrated to the 10 to 40 hours required by Zeewolde. The system uses hydrogen, iron, and water as raw materials, which are more abundant and lower in cost compared to lithium-ion batteries reliant on lithium, nickel, cobalt, and graphite, helping to alleviate strategic concerns regarding the supply chain.
This project is also a direct response to the increasingly severe grid congestion issues in the Netherlands. In February 2026, Dutch Climate Minister Sophie Hermans mentioned in a letter to parliament that regional grid operators had over 14,000 electricity offtake requests on their waiting lists, totaling approximately 9 GW, while national grid operator TenneT had 212 requests on its waiting list, amounting to 38 GW. The phenomenon of wind-rich regions hitting transmission caps is not unique to the Netherlands, but the country is currently one of the most typical examples. By deploying energy storage, the Zeewolde wind farm can store power when it cannot be immediately exported and release it when grid connections are available, thus avoiding the lengthy wait for transmission line upgrades.
Zeewolde is co-owned by over 200 local farmers, residents, and entrepreneurs. Once the energy storage system goes online, the project plans to rename itself Energiehub Zeewolde, marking a shift in its role from pure wind power export to actively managing the timing of electricity injection into the grid. The deployment will proceed in phases: Elestor will first install a smaller pre-commercial unit to verify performance, with the full 20 MW system targeted for completion by 2031. Prior to this, Elestor completed a $34 million (€30 million) Series A funding round led by Equinor Ventures, with participation from Vopak Ventures, Invest-NL, and others, reflecting institutional investors' genuine interest in long-duration energy storage technologies beyond lithium-ion batteries.
The driving force behind this trend extends far beyond the Netherlands. According to reports, renewable energy curtailment in the U.S. regional transmission organization PJM increased nearly sixfold in 2024, with similar transmission bottlenecks existing in Texas, California, Germany, and Australia. Short-duration lithium-ion storage is suitable for hourly load shifting but is not designed to address multi-day transmission constraints. For utilities and grid operators, the key factor limiting renewable energy development is gradually shifting from how much power can be generated to how much can be effectively delivered. Projects like Windpark Zeewolde are built precisely to fill this gap, with buyers increasingly valuing system flexibility, and duration becoming a more central metric than power capacity.
