How an iron-air battery works
Form Energy and Great River Energy, Cambridge MN: 1.5 MW · 150 MWh · up to 100 hours
Rusting iron makes electricity; un-rusting it stores electricity. Built for the multi-day stretches when wind and sun both go quiet. Fill it on a windy day, then carry the grid through four days of calm. Every number comes from one model.
Sources: Form Energy and Great River Energy, Cambridge Energy Storage Project (groundbreaking Aug 15, 2024; 1.5 MW / 150 MWh, up to 100 hours; expected online late 2025); POWER Engineering (chemistry; Xcel Becker 10 MW / 1,000 MWh; Georgia Power 15 MW / 1,500 MWh); Wikipedia, Form Energy (washing-machine-sized modules of 10–20 cells; cost claim under a tenth of lithium-ion). Form hasn't published round-trip efficiency; charging rate, enclosure count, weather and timing are illustrative.