Form Energy scales iron batteries for multiday grid storage

Form Energy is developing iron-based batteries designed to store electricity for 100 hours, positioning the technology as a cheaper alternative to lithium-ion systems for long-duration grid storage. The batteries rely on “reversible rusting”: oxygen converts iron to rust during discharge, releasing electrons, while charging turns the rust back into iron metal.

Commercial momentum has accelerated over the past two years. Form has started producing batteries at its West Virginia factory for a 150 megawatt-hour system with Minnesota electricity provider Great River Energy, scheduled to come online in 2027. Its largest announced deal is with Xcel Energy, where wind and solar power supported by 30 gigawatt-hours of Form batteries will power a new Google data center in Minnesota, with deployment expected in phases between 2028 and 2031.

The technology could help utilities rely less on fossil fuel plants during heat waves, deep freezes, or periods with little wind or sun. It may also help address rising electricity demand from AI data centers, which has delayed coal plant closures, spurred new natural gas plants, and increased consumer prices.

Scaling remains the central challenge. Form’s current production capacity is 2 gigawatt-hours of battery storage per year, far below the 80 gigawatt-hours promised through commercial agreements. The footprint is also large, with batteries requiring an acre for every two to three megawatts and the Google installation expected to occupy the equivalent of at least 75 football fields.