Elestor claims its hydrogen-iron flow battery delivers 75%+ round-trip efficiency, a 20-25 year lifespan, and 15€/kWh capex for long-duration storage. 
Dutch long-duration energy storage (LDES) developer Elestor has partnered with Windpark Zeewolde to deploy a 20MW/200-800MWh hydrogen-iron flow battery storage system at what is described as Europe’s largest onshore wind farm.
