Google is pairing its next U.S. data center with one of the most ambitious clean power packages on record, striking a 1.9-gigawatt deal that includes a 300-megawatt iron-air battery capable of discharging for 100 hours. The project, developed with Xcel Energy for a new facility in Pine Island, Minnesota, aims to push beyond daily solar smoothing and attack the harder problem of multi-day clean power reliability.
Inside the 100-Hour Battery Bet on Iron-Air Storage
The long-duration system comes from Form Energy, a U.S. startup commercializing iron-air batteries that store energy by rusting and then reversing that process. Unlike lithium-ion cells, which are designed for high efficiency and shorter-duration output, iron-air technology trades efficiency for ultra-low cost and multi-day endurance. Form has publicly targeted storage costs near $20 per kilowatt-hour—at least 3x cheaper than typical lithium-ion benchmarks—while accepting round-trip efficiencies in the 50% to 70% range compared with ~90% for lithium-ion.
At 300 megawatts sustained for 100 hours, the battery’s energy capacity reaches 30 gigawatt-hours. By energy, that would rank among the largest storage assets ever attempted and is designed to ride through wind lulls and cloudy stretches that can last days, not hours. For scale, 30 GWh is roughly enough electricity to power around 1 million average U.S. homes for a day, assuming typical residential consumption.
Wind, Solar, and Storage Built for 24/7 Operations
Under the agreement, Xcel Energy will add approximately 1.4 GW of wind and 200 MW of solar to feed the data center and charge Form’s battery, completing the 1.9-GW package when the battery’s rated power is included. The buildout reflects a shift from “annual matching” of clean energy to hourly—an approach sometimes called 24/7 carbon-free energy—where the goal is to meet demand with clean resources every hour of the year, not just on average.
Lithium-ion batteries dominate grid storage today, but their sweet spot is firming the evening peak for 2 to 8 hours. A 100-hour system is a different class of reliability tool. It addresses rare yet impactful weather patterns known as Dunkelflaute—extended periods of low wind and sun—allowing clean power to shoulder through instead of falling back to fossil peakers. Analysts at the National Renewable Energy Laboratory have long underscored the value of such long-duration assets as renewable shares rise.
A New Tariff Model to De-Risk Clean Tech
The deal also pioneers a utility tariff structure designed to bring emerging technologies onto the grid without shifting risk to general ratepayers. Building on a model Google first advanced with an enhanced geothermal purchase from Fervo, the “clean transition tariff”—also known as a clean energy accelerator charge—lets Xcel procure innovative projects that might face regulatory pushback, while Google pays a premium to cover the incremental cost and risk.
This alignment is notable because utility regulators are obligated to protect customers from uneconomic bets. The tariff structure gives utilities a path to scale promising technologies faster, with a creditworthy buyer absorbing the early-mover premium. If replicated, it could become a template for bringing next-wave clean resources—geothermal, long-duration storage, advanced nuclear—into rate-regulated markets.
Why It Matters for Data Centers and the Grid
Data centers are devouring ever more electricity as AI and cloud workloads expand. The International Energy Agency estimates data centers already account for roughly 1% to 2% of global electricity demand, and U.S. utilities from PJM to TVA have flagged unprecedented load growth ahead. The question is not just how to add clean megawatts, but how to ensure those megawatts are dependable during the hardest hours.
Long-duration storage directly addresses this reliability gap. The U.S. Department of Energy has identified multi-day storage as a keystone technology for high-renewable grids, enabling wind- and solar-heavy systems to maintain service during prolonged disturbances. For hyperscale buyers, it also reduces reliance on fossil backup and can materially lower carbon intensity in regions where renewable output swings widely week to week.
Form Energy’s Progress and Early Proof Points
Form is already installing an iron-air pilot in Minnesota with Great River Energy rated at 1.5 MW with 150 MWh of storage—enough to run full-tilt for 100 hours. The company manufactures in West Virginia and has raised about $1.4 billion, according to PitchBook, reflecting confidence that ultra-cheap, abundant iron can unlock a different cost curve than lithium, which is tied to more volatile global supply chains.
Critics point to the technology’s lower efficiency and physical bulk. But for resilience applications, energy cost per kWh and duration often matter more than efficiency alone. If a system is inexpensive enough to massively oversize and can sit for days waiting for rare events, it becomes an insurance policy for clean grids—paid for upfront and deployed only when the weather demands it.
For Google and Xcel, the payoff is a blueprint: blend high-capacity wind, complementary solar, and a multi-day battery under a purpose-built tariff, and you can run a power-hungry data center with cleaner, steadier electricity. If it performs as designed, expect other utilities and hyperscalers to copy the playbook.
