A rusting battery in Minnesota could unlock the electric grid of the future

A pilot project between Minnesota's second largest supplier of electricity, Great River Energy, and a Massachusetts start-up claims to have a breakthrough in battery technology that would allow for vast expansions of renewable energy on the power grid.

Iron pellets Form 2.jpg
Oxygen and iron are the key components of Form Energy's battery, which charges and discharges through a cycle of rusting and unrusting small iron pellets.
Contributed / Form Energy

BISMARCK — While the incoming owner of North Dakota’s largest coal-fired power plant, Coal Creek Station, is investing in an emerging fossil fuel technology to slash greenhouse gas emissions, the facility's current owner is betting on a different path to the same end: a breakthrough in battery technology that could allow for vast expansions of renewable energy on the power grid.

North of Minneapolis, Minnesota’s second largest electricity provider, Great River Energy, is looking to deploy a pilot scale battery with the capacity to cheaply store power for days at a time. It’s a prospect that could solve a fundamental problem in the country’s shift toward low carbon energy sources, providing renewably sourced power at times when the sun isn’t shining and the wind isn’t blowing.

And unlike the ingredients in today’s fleet of batteries, the key to the concept is an abundantly available element: iron. The resource could be supplied right there in Minnesota, the country’s leading producer of iron ore .

GRE’s project is a partnership with a buzzy — and, until recently, secretive — start-up called Form Energy, which claims to have achieved the coveted long duration storage prize at its lab in Cambridge, Massachusetts. The next step is to test their invention in the field, with plans to deploy a single megawatt battery into the GRE portfolio as soon as late next year. 

Form Energy mock-up.jpeg
A rendering of what Form Energy's one megawatt battery is expected to look once installed and operating in Cambridge, Minnesota.
Contributed / Form Energy

Ted Wiley, president and co-founder of Form, said the company is looking to provide a battery that can hold energy for 100 hours at a time, as much as 25 times the typical span of currently available batteries, all while driving down costs by a factor of 10 or more.


It’s an achievement that could be “a good, reliable replacement to coal and natural gas,” Wiley said. “All of the generation that’s currently provided by coal and natural gas could be provided by wind and solar augmented by batteries."

The idea represents a different pathway towards cleaning up the electric grid from the technology under the spotlight in North Dakota , carbon capture, which seeks to keep fossil fuels online. Resources like coal and natural gas provide a stable source of power generation at times when the conditions aren't right for wind and solar, a factor that was central to North Dakota's push for GRE to sell its 1,100 megawatt Coal Creek Station , in McLean County, rather than shut it down as the co-op said it would in early 2020. Now, Coal Creek's incoming owner, the Bismarck-based Rainbow Energy Center, is pursuing $1.5 billion plans to retrofit the plant for carbon capture, which would siphon greenhouse gases off the facility to make it a cleaner producer of power for the long-term.

For Wiley, a successful long-duration battery of the kind they’re developing at Form has the potential for massive adoption — reaching into the “terawatt scale,” or more than a million times the size of the company’s pilot in Minnesota.

Jon Brekke, vice president at GRE, said that in its partnership with Form the cooperative saw an opportunity to chase its climate goals and prioritize low costs for customers, all while supporting a new market for a core Minnesota resource.

“We used iron from Minnesota mines to help build the country,” he said. “Now we can use iron from Minnesota mines to help maintain reliability and cost effectiveness of a very quickly transforming power grid.”

Iron and air

Today, the batteries powering electric cars and parts of the national electric grid are made from lithium and other relatively scarce metals like nickel, cobalt and manganese. These lithium-ion units cap out after just a few hours of storage, and their inputs can be costly, even posing human rights concerns at mining sites in some parts of the world.

Iron, on the other hand, is low cost and naturally abundant.

And Form's innovation, Wiley explained, is relatively simple: its batteries take in oxygen from the air, causing small iron pellets inside to rust, releasing electrons in the process. The “magic” is in the next step, said Wiley, when the battery breathes out air again and reverses the rust back to fully metallic iron, a cycle that charges and discharges the battery.


“It's dead simple. It's extremely low cost. It's safe. And it's really effective for storing multiple days of energy,” Wiley said.

Form Energy lab.jpg
Amelie Kharey, a battery engineer at Form Energy, adjusts a battery cell in one of the start-up's labs.
Contributed / Form Energy

And though iron is too heavy for use in electric vehicles, its batteries have a longer lifespan than the current lithium-ion technology.

A lithium-ion battery may last for around seven to 10 years, while iron-based batteries can easily last for more than 20, said Massoud Amin, a professor of electrical engineering at the University of Minnesota who specializes in power grid systems. And unlike batteries in our iPhones, micro versions of the lithium-ion batteries found on the power grid, iron flow batteries don’t see their capacity degrade over time.

All of these qualities add up to much lower storage costs, so that with iron, “the equation changes,” Amin said.

Form, which began research into power grid solutions in 2017 and entered its partnership with GRE the next year, kept the specifics of its project under lock until last year.

Since announcing its one megawatt pilot in Minnesota, the small start-up has prompted big expectations in energy circles. Last August it closed out a $240 million fundraising round, and it counts Breakthrough Energy Ventures, a climate investment fund backed by Microsoft founder Bill Gates and Amazon founder Jeff Bezos, among its investors.

Still, Form is charting a course others have pursued before. Scientists with NASA and GTE first began exploring the potential of iron-air batteries in the 1960s, and the company Westinghouse Electric Corporation pushed the research further in the 1970s . But those early trailblazers eventually abandoned the technology. There just wasn’t a need for a battery with days of storage capacity at the time, especially one with iron's weight, Wiley said.

It’s a different world today, as regulators and energy providers are under mounting pressure to take bold steps to mitigate climate change, pressures that have spurred a race for technologies that eliminate greenhouse gas emissions without sacrificing the stability of the grid.


On that score, Minnesota presented Form with a “perfect problem statement” to test its battery, Wiley said: winter blasts and extreme, subzero temperatures that can affect the reliability of the grid for days.

Replacing coal?

If Form’s battery is successful, Wiley said, it could help to unleash wind in neighboring North Dakota, where turbines are prevalent but have yet to capture the extent of the state’s renewable resource.

GRE is on pace to supply half of its electricity from wind power by 2025 and more by 2030, and Brekke said finding a way to store energy from those renewable sources is central to its long-term climate ambitions. Form's one megawatt pilot could power up to 400 Minnesota homes for days, but if it works, Brekke said GRE could move to much larger installations, ranging in the hundreds of megawatts.

The co-op also plans to keep buying power from Coal Creek Station for the next 10 years, and Brekke said he’s supportive of efforts there to pursue carbon capture and storage.

Coal Creek is one of two ventures to retrofit a coal plant for carbon capture in North Dakota, alongside Minnkota Power Cooperative’s Project Tundra. In recent years coal has struggled to compete with cheap natural gas and ascendant renewable sources, leading to many plant closures around the country, but North Dakota leaders have embraced nascent carbon capture technology as the pathway to making its fossil fuel power plants cleaner and more sustainable for the long-term.

Photo: Coal Creek Station
Great River Energy's Coal Creek Station near Underwood, N.D.
Special to The Forum

Jason Laumb, director of Advanced Engineering Systems Initiatives at the University of North Dakota’s Energy and Environmental Research Center, said he sees technologies like carbon capture and batteries as equally important, and potential complements to one another on the electric grid over the next two decades.

While batteries come with enormous benefits, among them the ability to dispatch electricity almost instantaneously, they need a lot of real estate, Laumb said. Even a single megawatt of battery storage can take up several acres of land.

Wiley said he sees efforts like carbon capture as an important piece in the larger project of tackling climate change, an ambition he said is going to need “several shots on goal.” It's not clear how any of these new technologies will scale, he noted.


And though long-duration batteries could respond to a need currently filled by coal and natural gas, Wiley said there need to be partnerships between government and industry to ensure that fossil fuel communities have a place in the clean energy economy. The iron-air battery can't just work for the big cities, Wiley said, and its ramifications for North Dakota will be a litmus test of its success.

“If we can't figure out a way for this to work for North Dakota, this doesn't work,” he said.

Readers can reach Forum reporter Adam Willis, a Report for America corps member, at

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