Great River Energy, a Minnesota electric cooperative, and Form Energy, a Massachusetts battery company, are building an iron-air battery in Cambridge, Minnesota. MIT Technology Review reported on October 6, 2026, that it is set to come online in 2027.
The project at a glance
| Item | Reported detail | Source |
|---|---|---|
| Cambridge project | 1.5 MW, 150 MWh, up to 100 hours (about four days) at full power; groundbreaking August 2024 | Power Engineering |
| Expected start | 2027 (earlier plans said late 2025) | MIT Technology Review; Great River Energy |
| Xcel Energy and Google project | 30 GWh, 300 MW, Pine Island, MN; phases 2028 to 2031 | Facilities Dive; MIT Technology Review |
| Weirton factory | $760 million; 750 jobs targeted by 2028; about 450 staff in 2026 | Capito release coverage; Boston Globe |
Rust, on purpose
Form’s battery uses iron, air and water. On discharge, iron reacts with oxygen and rusts, releasing electricity. On charge, electricity turns the rust back into iron. Iron is cheap and widely available.
The price is efficiency. Facilities Dive reports round-trip efficiency of about 40% to 50% for iron-air systems, well below lithium-ion, and the systems take up a lot of room: Technology Review says about an acre per 2 to 3 MW.
So nobody is pitching this against lithium-ion for daily cycling. The job is covering stretches when wind and solar output stay low for days. Cambridge is the first commercial deployment of the technology, and Great River Energy plans a multi-year study of how it performs once it’s built, according to Power Engineering.
Why It Matters to You
- If you’re a Great River Energy member, the battery is meant to help the co-op’s grid ride out multi-day gaps in wind and solar. It isn’t running yet; 2027 is the expected start.
- It is a grid system, not a home product, so it won’t power individual buildings.
- No source shows lower electric bills yet. The first commercial project is mainly a test of whether the technology works and what it costs.
What isn’t settled
The battery is not running. Great River Energy’s project page still said end of 2025, but Technology Review now says 2027, so 2027 is the date to go by. No source we opened says how many homes the system could power, and power use per home varies too much to convert reliably. Form’s goal is $20 per kilowatt-hour, which it says would be competitive with natural gas, but Form declined to share current costs and Facilities Dive notes the target dates from about five years ago. A third-party estimate for the Google project is about $33 per kWh, and a Penn State professor said iron-air would be competitive at about $50 per kWh. Production is about 2 GWh a year, far below the 80 GWh promised in commercial agreements, per Technology Review. At Weirton, a 2024 release covered by Senator Capito’s office cited 380 workers at the start and a target of 750 full-time jobs by 2028; in August 2026 the Boston Globe put headcount at about 450.
Quick answers
Is it really made of rust? The battery stores energy by reversibly rusting iron. Form describes it as using iron, air and water, so “iron-air” is the usual name.
Can it power a house for four days? It is a grid system at 1.5 MW, not a home product. It serves the cooperative’s grid, not individual buildings.
Will it lower electric bills? No source shows that yet. Economics are uncertain because multi-day batteries cost a lot to build and may sit idle often.
Who else is buying this technology? Xcel Energy plans 30 GWh of Form batteries with wind and solar for a Google data center in Minnesota, in phases between 2028 and 2031.
Sources
- MIT Technology Review: 2026 Climate Tech Companies to Watch: Form Energy and its iron batteries (Oct 6, 2026)
- Facilities Dive: Facilities betting big on low-cost 100-hour iron-air batteries (Aug 26, 2026)
- Power Engineering: Minnesota co-op breaks ground on multi-day energy storage project (Aug 21, 2024)
- Great River Energy: Cambridge Energy Storage Project (accessed Oct 13, 2026)
- Sen. Capito: Weirton-made Form batteries heading to Maine for new project (Aug 9, 2024)
- Boston Globe: Form Energy raises $750 million (Aug 12, 2026)