Energiehub Zeewolde Hydrogen-Iron Flow Battery

Executive Overview

The Energiehub Zeewolde Hydrogen-Iron Flow Battery is a planned 20 MW long-duration energy storage system with a duration of 10 to 40 hours and a total capacity of 200 to 800 MWh, to be deployed in phases by Dutch storage developer Elestor at Windpark Zeewolde, a 322 MW community-owned onshore wind farm in Flevoland province, the Netherlands, described as Europe's largest onshore wind farm. Announced on 7 July 2026, the project pairs long-duration storage directly with large-scale wind generation to address the grid congestion that prevents the wind farm from exporting all available generation during peak periods. With the addition of storage, Windpark Zeewolde — owned by more than 200 local farmers, residents and entrepreneurs — will be renamed Energiehub Zeewolde as it evolves into an integrated hub combining renewable generation, storage and flexible consumption. The project is in early development.

How It Works & Differentiation

Elestor's hydrogen-iron flow battery stores energy in liquid electrolytes held in external tanks, combining a hydrogen gas circuit at the anode with an aqueous iron-based electrolyte at the cathode. During charging, electricity drives an electrochemical reaction that produces hydrogen, which reacts with the iron electrolyte; discharging reverses the reaction to deliver electricity back to the grid. Because power (stack size) and energy (electrolyte volume) are decoupled, energy capacity scales by adding low-cost electrolyte without duplicating power infrastructure — Elestor states that durations of 8 to 150 hours are achievable, well beyond the four-hour range typical of lithium-ion systems. The chemistry relies on abundant hydrogen and iron rather than lithium, cobalt or vanadium, and the company reports system-level round-trip efficiency above 75%, stable performance over tens of thousands of cycles, and a projected 20 to 25 year operating life. The battery will connect directly to the wind farm's energy infrastructure via the Vogelweg High Voltage Station, allowing generation and storage to operate as an integrated system.

Commercialization & Traction

The project marks the first large-scale commercial application of Elestor's technology and follows the company's EUR 30 million Series A round led by Equinor Ventures, with participation from Vopak Ventures, Invest-NL, Somerset Capital Partners, EIT InnoEnergy and Enfuro Ventures. Deployment is structured in phases: Elestor will first install its final pre-commercial unit at the site to demonstrate performance and market readiness in a real-world use case, followed by a commercially ready production battery, with the system scaling toward the full 800 MWh configuration as performance and the commercial case are proven. No commercial operation date has been confirmed by either partner; trade reporting indicates the full 20 MW system is targeted for 2031.

Scalability & Strategic Context

Grid congestion is a systemic constraint across the Netherlands, where renewable generation growth has outpaced transmission capacity, and the project is intended to demonstrate how long-duration storage can raise utilisation of existing grid connections rather than waiting for network reinforcement. Storing wind energy during periods of high output and dispatching it when demand rises or grid capacity becomes available directly reduces curtailment at one of Europe's largest onshore wind sites. Success at Zeewolde would provide a replicable template for pairing multi-day storage with constrained renewable assets across Europe, and would validate hydrogen-iron flow chemistry in a segment of the long-duration storage market where flow battery developers have historically struggled to reach commercial scale.