Google has agreed to back a large-scale iron-air battery system to supply power for a data center in Minnesota, a deal that routes an unusual energy storage technology into one of the most electricity-hungry sectors of the American economy. The arrangement, which involves utility giant Xcel Energy and battery maker Form Energy, ties a chemistry based on the rusting and de-rusting of iron to the steady, round-the-clock demand of cloud computing infrastructure. If the system performs as designed, it could reshape how tech companies think about bridging gaps in renewable power.
How Rusting Iron Stores Electricity
The core technology behind this project is deceptively simple. Iron-air batteries generate electricity by exposing iron to oxygen, allowing the metal to oxidize and release energy in the process. Charging the battery reverses that reaction, stripping oxygen away and restoring the iron to its original metallic state. A technical overview from Sandia researchers through the U.S. Department of Energy describes this cycle as “reversible rusting” and frames the technology as capable of multi-day energy storage duration.
That multi-day capability is the feature that separates iron-air batteries from the lithium-ion packs now standard in grid storage and electric vehicles. Lithium-ion systems typically discharge over a window of two to four hours, which is useful for smoothing short spikes in demand but inadequate for covering extended periods when wind turbines sit idle or clouds block solar panels. Iron-air cells, by contrast, are engineered to discharge steadily across far longer stretches, making them better suited to fill the kind of prolonged gaps that renewable-heavy grids routinely face.
The tradeoff is energy density. Iron-air batteries are physically large relative to the power they deliver, and their round-trip efficiency (the share of input energy recovered on discharge) trails lithium-ion by a meaningful margin. For a fixed site like a data center, though, physical footprint matters less than it does for a vehicle or a portable device. What matters more is cost per unit of stored energy and the ability to keep power flowing when the grid cannot.
Why Data Centers Need Multi-Day Storage
Data centers are not like factories that can throttle output when electricity prices spike. They run continuously, and even brief interruptions can cascade into service outages affecting millions of users. As artificial intelligence workloads have driven sharp increases in computing demand, the electricity appetite of these facilities has grown in step. That growth has collided with corporate climate pledges, creating pressure to find clean alternatives to the natural gas peaker plants and diesel generators that traditionally serve as backup power.
Google’s interest in iron-air storage reflects a specific operational problem. The company has committed to running its operations on carbon-free energy around the clock, not just on an annual net basis. Meeting that standard in a northern climate like Minnesota, where solar generation drops significantly in winter and wind output can be inconsistent for days at a time, requires storage that can ride through extended lulls. A battery that lasts hours is not enough. A battery that lasts days changes the math.
Form Energy, the company manufacturing the iron-air cells, has positioned its product squarely at this use case. The company’s pitch centers on the low cost of iron as a raw material compared to lithium, cobalt, and nickel, the metals that dominate conventional battery supply chains. Iron is abundant, domestically sourced, and not subject to the same geopolitical supply risks that have complicated lithium-ion procurement. For a buyer like Google, which needs to plan infrastructure investments years in advance, supply chain stability carries real strategic weight.
The Regulatory Path Through Minnesota
Deploying a new battery technology at utility scale is not simply a matter of buying hardware. In Minnesota, the deal between Google and Xcel Energy requires an Electric Service Agreement that must be filed with the Minnesota Public Utilities Commission. The Commission’s regulatory docket portal serves as the authoritative public record for such filings, including any tariff or rider arrangements that allow the utility to recover costs associated with the battery installation.
This regulatory step is where the project’s economics become visible. Under a Clean Energy Adjustment Clause, or CEAC, Xcel Energy can seek approval to pass certain costs of clean energy investments through to ratepayers. The Commission must review the filed agreement, any associated tariff proposals, and public comments before issuing an order. That process determines not just whether the project moves forward, but how its costs are distributed between Google, the utility, and ordinary electricity customers in the service territory.
For Minnesota ratepayers, the question is whether the cost recovery structure insulates them from bearing disproportionate risk on an unproven technology. Iron-air batteries have not yet operated at commercial scale for extended periods, and the performance data available in public technical literature comes largely from laboratory and pilot settings. The Commission’s review of the Electric Service Agreement and any supporting technical filings will be the primary checkpoint where those risks are weighed against the potential grid benefits.
What Iron-Air Gets Right and Wrong
Much of the coverage around iron-air batteries has treated the technology as a straightforward win: cheap materials, long duration, domestic supply. That framing skips over real limitations. The round-trip efficiency gap means that more energy is lost in each charge-discharge cycle compared to lithium-ion, which raises the effective cost of every kilowatt-hour delivered. The physical size of the battery modules requires significant land area, and the technology’s degradation profile over thousands of cycles has not been validated at commercial scale in public, peer-reviewed data.
There is also a timing question. Form Energy has announced plans for domestic manufacturing, but large-scale production timelines for new battery chemistries have historically slipped. If the Minnesota installation depends on modules from a factory that is still ramping up, the project’s operational date carries uncertainty that neither Google nor Xcel Energy has fully addressed in public statements. Delays would not just push back the start of service. They would also postpone the learning that regulators and other utilities are looking for.
Still, the strategic logic is sound. No other commercially available storage technology offers multi-day duration at a cost point that makes economic sense for grid-scale deployment. Pumped hydro storage can match the duration, but it requires specific geography and years of construction permitting. Compressed air storage faces similar siting constraints and often depends on underground caverns. Iron-air occupies a niche that, if the manufacturing and performance challenges are resolved, has no direct competitor at the price point Form Energy has targeted.
Broader Implications for Grid-Scale Storage
The Minnesota project is more than a one-off experiment for a single data center. If it works, it will provide a template for how utilities and large corporate customers can jointly finance and regulate long-duration storage. The structure of the Electric Service Agreement, the allocation of risk between the parties, and the way the Commission treats cost recovery under the CEAC will all be closely watched by regulators and utilities in other states.
For the tech industry, success would validate a path toward 24/7 carbon-free electricity that does not rely solely on buying renewable energy credits or signing contracts for distant wind farms. It would demonstrate that on-site or near-site storage can shoulder a larger share of reliability needs, reducing dependence on fossil-fueled peaker plants. That, in turn, could ease local opposition to new data centers by showing that their growth can be aligned with regional decarbonization goals.
For the broader grid, iron-air batteries could become one piece of a more diversified storage stack. Lithium-ion systems would continue to handle short-duration balancing and fast response. Long-duration technologies like iron-air would cover multi-day weather events and seasonal mismatches. Together, they could allow higher penetrations of wind and solar without a corresponding expansion of gas-fired backup.
None of this is guaranteed. The Minnesota installation must prove that iron-air batteries can perform reliably outside the lab, that maintenance costs remain manageable, and that communities are comfortable hosting large battery sites. It must also show that regulators can thread the needle between encouraging innovation and protecting ratepayers. But by pairing a demanding customer, a major utility, and a novel technology under the scrutiny of a state commission, the project offers a rare, concrete test of whether long-duration storage is ready to move from promise to practice.
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*This article was researched with the help of AI, with human editors creating the final content.
