‘Rusty’ batteries could hold key to Minnesota's carbon-free power future

Iron-air battery system is seen
An artist’s rendering of a 56-megawatt iron-air battery system, developed by Boston-based Form Energy. Great River Energy plans to install a much smaller, 1.5-megawatt iron-air battery pilot project next to its natural gas peaking plant in Cambridge, Minn., next year. Xcel Energy is planning to install a 10-megawatt battery system in Becker, Minn. where it’s building a large solar project.
Courtesy of Form Energy

Updated 8:30 a.m.

In central Minnesota, a first-of-its kind pilot project will test whether new battery storage technology that uses a common process — iron rusting — could play a key role in the nation's transition to cleaner energy.

Great River Energy plans to install a 1.5 megawatt iron-air battery system next to its natural gas peaking plant in Cambridge, about 45 miles north of the Twin Cities, sometime next year.

“What's exciting about doing this pilot — leading the charge — is we're going to get to learn about what capabilities these batteries really hold,” said Aaron Hanson, energy program specialist for leadership and education at the University of Minnesota's Institute on the Environment.

Capturing excess energy for later use

Interest in battery storage is surging as electric utilities retire baseload power plants that burn coal or gas, and add more wind and solar.

This week, Minnesota Gov. Tim Walz signed a bill setting a 2040 deadline for electric utilities to transition to carbon-free sources of power.

Energy storage will be critical, Hanson said, as Minnesota and the U.S. shift away from burning fossil fuels to generate electricity to renewable sources that don't contribute to climate change, but don't always produce energy consistently.

“We can capture excess energy when it's being produced, and save it and then use it for when the wind isn't blowing, or the sun isn't shining,” Hanson said.

Great River Energy's will be the first iron-air battery project in Minnesota. It will be followed closely by Xcel Energy, which plans to install a 10-megawatt system next to its coal-fired power plant in Becker. Xcel plans to retire the Sherco coal plant by 2030 and build a massive solar project on the site.

“For us, this is really an important test to figure out how energy storage can complement a great deal of renewables on our system, and to help us with the clean energy transition,” said Chris Clark, president of Xcel in Minnesota, North and South Dakota.

Sherco is visible across a farm field
The Sherburne County Generating Station, or Sherco, is visible across a farm field outside of Becker, Minn. The Minnesota Public Utilities Commission recently approved site and route permits for a 460-megawatt solar project on land next to the coal plant that will utilize the existing electrical infrastructure.
Kirsti Marohn | MPR News

Key problem

Both utilities are using technology developed by Boston-based Form Energy. Mateo Jaramillo, the company's co-founder and CEO, formerly worked on battery storage at Tesla.

Jaramillo set out to solve a key problem with more variable energy sources: How to store up enough power not just for a few hours like a lithium battery, but multiple days at time, such as during a heat wave or extreme cold snap?

“Think about covering a polar vortex,” Jaramillo said. “That's probably the easiest way to sort of wrap your mind around what kind of battery you need to really drive that deep decarbonization of the electric system.”

Form Energy's battery can store electricity for 100 hours, compared to about four hours for a lithium battery. And it's made of iron, an element that's abundant around the world, including on Minnesota’s Iron Range.

It uses an electro-chemical process called oxidation, or rusting. 

The battery takes in oxygen from the air and converts the iron to rust. Applying an electrical current converts the rust back to iron. Repeating the rusting and unrusting process allows the cell to charge and release electricity.

Jaramillo said Minnesota's plentiful supply of iron is part of its appeal for a launching ground, as the company looks to scale up its technology. 

“We are very actively investigating what it would take to be able to use that as a resource,” he said. 

It’s not as simple as taking iron ore from the ground and putting it into a battery, though. Jaramillo said the batteries require a type of iron that's been reduced and purified.

A low-cost storage solution

Still, iron-air batteries offer other advantages. They're cheaper than lithium, work in extremely cold weather and don't contain toxic materials. Most of their components can be recycled.

There are some drawbacks. They're big and heavy, and less efficient than lithium. 

“Every storage solution has trade-offs,” Jaramillo said. “There is no perfect battery that weighs nothing, costs nothing and lasts forever. That thing doesn't exist.”

It may not be perfect, but the U of M’s Hanson calls long-duration battery storage a “game changer” that could make the grid more reliable, allowing utilities to store electricity when there's plenty of it, and release it when it's most needed.

“Having this new technology on the grid now makes our grid better than it was before, actually reducing the risk of outages,” Hanson said.

‘Missing ingredient’

Great River Energy will be testing the battery's performance, durability and economic benefits when it installs the system in Cambridge next year, said Jon Brekke, vice president and chief power supply officer.

Longer-duration storage is “a missing ingredient” in the move towards renewable energy, Brekke said. If the pilot is successful, he envisions Great River pursuing much larger battery projects in Minnesota as it adds more wind energy to its system.

“We can absorb excess energy at times of high production, and then we can release energy when we need it — to power the grid, and to keep the system reliable and to keep costs affordable for consumers,” Brekke said. 

Xcel and Great River say they can envision the large battery systems stationed near large wind or solar farms, to help manage how they put the energy those resources generate onto the grid.

Xcel’s Chris Clark said he expects the utility will use a mix of different storage technologies, including lithium-ion batteries. But lithium is much harder to come by than iron, he said.

“For us, to be able to use a commodity that we have right here in Minnesota, and be able to incorporate that into the battery — we're really excited about that,” Clark said.