Renewable generation sources like wind and solar have gained significant ground in the past decade. But most experts agree that fully realizing the potential of these promising technologies will require an even greater breakthrough: economically viable, large-scale, long-term energy storage.

An experiment by Great River Energy just might make it happen.

The G&T based in Maple Grove, Minnesota, is installing an “aqueous air battery” prototype that will provide 1 MW of power for up to 150 hours, with the promise of future grid-scale deployment, at a fraction of current storage costs.

Greg Padden, GRE’s director of resource planning and markets, says the pilot project, expected to come on-line in 2023, reflects the G&T’s commitment to a “cost-competitive portfolio” for its 28 distribution co-ops across Minnesota and their 700,000 member-owners.

“We’re in a very wind-rich part of the country, and that, combined with technology advancements, has made wind power the lowest-cost option for our members,” he says. “That’s very much a driver for this project.”

Great River Energy will generate more than 25% of its power this year from renewable resources, primarily wind, he says, and has set a goal of 50% renewables by 2030.

U.S. Energy Information Administration numbers show wind and solar as the fastest expanding generation sources nationwide, and storage capacity is on a similar trajectory, set to grow from 523 MW in 2019 to 7.3 GW in 2025, according to Battery Energy Storage Overview, a report from NRECA’s Business & Technology Strategies group.

But the rapid growth in wind and solar is exposing the limits of current storage systems.

“You can have a certain amount of renewable energy on the system and be fine,” says Jan Ahlen, NRECA energy solutions director. “But as you increase the amount, you run into problems of system stability, and storage makes a difference at that point. It becomes important to have that backup power, long-duration storage to assure you have reliable power during times the sun’s not shining or the wind’s not blowing.”

The problem, Ahlen says, is that lithium-ion batteries, currently the dominant technology, are suited to providing backup power over hours, not days, with a maximum duration in most cases of six hours or so. They also remain relatively expensive. While the price of lithium-ion batteries has fallen significantly, down 89% in the last decade, costs are projected to fall at a slower rate in the future, according to the NRECA report.

And the industry could see price spikes for minerals like lithium, nickel, and cobalt, on which lithium-ion technology depends, as electric vehicles and short-duration storage systems grow in popularity, the report notes.

“Because of this, lithium-ion batteries are unlikely to provide an economical long-duration energy storage option,” it concludes.

That means finding alternatives is a priority.

Cost and duration

The U.S. Department of Energy and several companies are working on new battery chemistries that can offer economical storage over a longer duration, and new technologies appear to be on the horizon. These include flow batteries, a form of rechargeable fuel cell, and a zinc-hybrid cathode battery developed by Eos Energy Storage.

“There are some contenders out there,” Ahlen says. “But there hasn’t been a technology yet that has really come out and said, ‘We’re going to be the next big thing over the next five years.’”

If Great River Energy’s aqueous air battery operates as advertised, he says, it could make a big difference: “I think it does have a ton of promise for the industry as a whole and co-ops in particular as they move toward more renewable energy.”

Padden says Great River Energy looked at both existing and upcoming battery storage options.

“We not only benchmarked this technology against what was out there but what was in development,” he says. “We think this technology holds great potential.”

Form Energy, the Massachusetts-based company that owns the aqueous air battery technology, was launched in 2017 by storage industry veterans in search of an affordable, longer-term battery solution, co-founder and President Ted Wiley says.

“The main challenge we had identified with energy storage is cost, and that is what we are attempting to bring down: the cost of energy storage on a dollars-per-kilowatt-hour basis,” Wiley says. “We’re targeting a 90-plus-percent reduction in the cost of a kilowatt-hour of energy storage to enable more deployment of renewable energy.”

Even if the cost of storage declined by 50%, he adds, current technology is economically viable for only a few hours.

“Our hypothesis going into this was that we need more than four to six hours,” Wiley says. “We need tens of hours or possibly greater than a hundred to unlock the potential of renewable energy to transform the grid.”

Wiley says the company expects to be able to share more about how its aqueous air battery works soon.

“What I can say now about the technology is that one of the main reasons it’s low cost is because it uses abundant materials—abundant materials that are available in the United States,” Padden says. “It isn’t relying on exotic components.”

‘A steppingstone’

Padden notes that viable long-term storage has industry-changing implications, such as allowing power producers to shift energy production seasonally.

“We’ll be able to cost-effectively store energy from wind, which has its best production in the spring and fall, and shift its availability to the winter and peak months,” he says.

He says Great River Energy had a firsthand look at the difference storage could have made last winter when a polar vortex, which brought temperatures of 25 degrees below zero, gripped its service territory for three days. Prices in the wholesale power market soared to $160 per MWh, a cost that could have been hedged if they’d had a 150-hour grid-level storage system operating.

The aqueous air battery is being installed at Great River Energy’s peaking power plant site in Cambridge, Minnesota. If the system is successful, the G&T hopes it will lead to larger deployments.

“This is a steppingstone,” Padden says. “While this project only provides 1 MW, the technology is being developed very much with an eye toward larger, grid-scale projects. It’s intended to be scalable to hundreds of megawatts in size.”

Form Energy’s Wiley says the company hopes the Great River Energy project “will act as a lighthouse, showing a path to the kind of storage capabilities and costs required for renewable energy to be the main source of power for grids around the world.”

“Our vision is renewable energy plus storage that is just as reliable and just as dispatchable as thermal generation [coal, oil, and gas] without trade-offs in cost or reliability,” he says.

That could spur a significant transformation of the grid, Ahlen says.

“You could see a grid that is more distributed, where, instead of having very large power plants in operation, you have more distributed operations; you have generation spread out over the grid,” he explains. “You also have a more flexible system, where you can use energy you have in storage multiple ways.”

More than half of states have renewable energy portfolio standards designed to promote wind, solar, and other renewable generation, Padden says, and longer-duration storage could help cooperatives manage that transition.

“We think it ultimately positions co-ops to continue serving their members in a future that looks different from what we see today.”