Iron Batteries That Store Power for 100 Hours Could Feed AI's Hunger
AI's appetite for electricity is colliding with the push to ditch fossil fuels. Data centers are delaying coal plant closures, prompting new natural gas builds, and raising consumer power bills. Form Energy thinks the fix is rust — specifically, iron-air batteries that store energy for 100 hours. The company is now ramping production and signing commercial deals that could reshape how grids handle the AI boom.
Why 100-Hour Storage Changes the Grid Math
Solar and wind are now cheaper than fossil fuels in most places, but their output swings with weather, seasons, and time of day. Lithium-ion batteries — the fastest-growing storage option — typically store only four to six hours of energy and rely on pricey metals that are costly to scale. Form Energy's iron-air batteries, by contrast, use cheap, abundant iron and a process the company calls "reversible rusting": oxygen turns iron into rust during discharge, and current converts it back during charging. That allows multiday storage, covering supply gaps during heat waves, deep freezes, or long stretches of low sun and wind — exactly the imbalances that keep natural gas plants running.
The Commercial Deals Taking Shape
Form has started producing batteries at its West Virginia factory for its first commercial deployment: a 150 megawatt-hour system for Minnesota electricity provider Great River Energy, set to come online in 2027. The largest deal so far is with Xcel Energy, another Minnesota utility, where wind and solar backed by 30 gigawatt-hours of Form's batteries will power a new Google data center, coming online in phases between 2028 and 2031. Form says its cost target is $20 per kilowatt-hour, which would make the systems competitive with natural gas alternatives. The company declined to share current pricing.
Scaling Is the Hard Part
Form's existing production capacity is 2 gigawatt-hours per year — a fraction of the 80 gigawatt-hours promised through commercial agreements. The company is outfitting its factory with new equipment and raised additional financing in August, bringing total funds raised, plus West Virginia state and US federal grants, to more than $2 billion. Physical footprint is another open question: the shipping-container-sized enclosures require an acre for every two to three megawatts, meaning the Google installation alone would span at least 75 football fields. Form also faces competition from pumped hydropower, compressed gas, fuel cells, gravitational devices, and flow batteries. Multiday storage economics remain tricky — large capital costs, frequently idle assets — so proving reliable delivery at scale is the real test.
Key Takeaways
- Form Energy's iron-air batteries store energy for 100 hours using a "reversible rusting" process with cheap, abundant iron.
- The company's first commercial project is a 150 MWh system for Great River Energy, due online in 2027.
- A 30 GWh deal with Xcel Energy will back a Google data center, phasing in between 2028 and 2031.
- Form's current capacity of 2 GWh per year falls far short of the 80 GWh promised in commercial agreements.
- Cheap long-duration storage could help renewables meet AI-driven electricity demand without new fossil fuel plants.
Source: MIT Tech Review • 🇺🇸 San Francisco
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