This story about Cache Energy’s new kind of thermal battery that could warm campus buildings using stored wind energy was originally published by Canary Media.
Twenty-one years ago, the University of Minnesota, Morris, became the first U.S. public university to draw power from an on-site, industrial-scale wind turbine. It added a second one in 2011. Today, the pair — affectionately known as Bert and Ernie — produce more power each year than the semirural campus consumes.
“It’s windy year-round here in western Minnesota,” said Troy Goodnough, the school’s sustainability director.
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Together, Bert and Ernie crank out 10 million kilowatt-hours of electricity annually. According to Goodnough, UMN Morris consumes about half the output and sells the rest to the Otter Tail Power Co., the local investor-owned utility. Now, a first-of-its-kind thermal battery pilot is underway that, if scaled up, could help the campus use more of that juice while reducing the environmental impact of the sprawling methane-powered steam-heat loops that keep it cozy through Minnesota’s bitter winters.
Late last month, technicians from Illinois-based Cache Energy arrived on campus to install the thermal battery unit, which transforms electricity into intense heat. Its outlet temperature can reach 1,000 degrees Fahrenheit — more than hot enough to efficiently run a steam heating system.
It took two hours to position the shipping container that houses the unit next to the school’s carpentry shop, and then another few hours to connect the unit to the building’s electrical and duct systems. It powered up on March 24 and hasn’t stopped providing heat since, Goodnough said. Its task is not small, he added: The “warehouse-like” shop has high ceilings and several thousand square feet of floor space.
“The cool thing is it’s doing what it’s supposed to be doing,” he said. “It’s working great.”
The thermal battery unit contains limestone-derived pellets coated in a proprietary binder that keeps them intact throughout their 30-plus-year operating life, according to Cache. When exposed to a stream of moist air, the pellets get so hot they “can be used to make hot air or even vaporize water to make steam,” Goodnough wrote last month. To recharge, the system uses electricity to dry out (and cool down) the pellets.
Ideally, that electricity is cheap, clean, and otherwise at risk of curtailment, said Sydnie Lieb, an assistant commissioner for regulatory analysis with the Minnesota Department of Commerce. Lieb’s agency helps fund Minnesota Energy Alley, a public-private partnership that supports the Cache project and other cleantech demonstrations in the North Star State.
“The most cost-effective place for thermal batteries is going to be where you have a lot of excess energy being produced where you don’t have a lot of transmission or [customer] load,” Lieb said.
Western Minnesota certainly fits the bill. The wind farms that dot the open, rolling landscape here and in neighboring North and South Dakota routinely produce more energy than the grid can handle. The Midcontinent Independent System Operator, the nonprofit that manages Minnesota’s grid, throttled hourly wind generation by an average of 508 megawatts in 2023, according to the U.S. Energy Information Administration. That’s the equivalent of what’s produced by about 160 newish onshore wind turbines. The Southwest Power Pool, which manages the grid for the wind-rich region stretching from North Dakota to the Texas Panhandle, curtailed wind output by an average of 1,097 MWthat same year.
Arpit Dwivedi, Cache’s founder and CEO, said low-cost electricity helps make the economic case for customers to invest in thermal batteries rather than stick with equipment that runs on natural gas, which is also plentiful in the United States’ midsection.
“We know gas is cheap,” he said, and that’s a problem for tech developers looking to electrify heat.
Another issue for big energy users, like UMN Morris, is that switching from gas to electric heat means replacing massive, long-lived boilers — likely fully paid for — with new equipment that needs to be leased or financed.
That shift is necessary if the university is going to meet its aggressive climate goals of reducing greenhouse gas emissions by 87% by 2035 and reaching carbon neutrality by 2050, but it could incur a considerable balance-sheet burden. So from the outset, Dwivedi and his team were intent on reducing Cache units’ upfront cost, he noted.
“We knew that if we did not have a low-capex system, we would not have an economic advantage,” he said.
Like other emerging thermal battery designs, Cache’s uses low-cost — if heavy — materials that are widely available in the United States. The primary inputs are steel, lime, and water, all of which Cache sources domestically, Dwivedi said. The proprietary binder that keeps the lime granules stable is by far the most expensive input, so the company focused on keeping that cost in check. Its secret ingredients are available domestically, too, Dwivedi added.
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Cache offers its thermal battery as a lease product that it says bundles the battery unit, delivery, installation, maintenance, guaranteed uptime, and takedown “without capital burden.” Just as an automaker leases a passenger vehicle, Cache retains ownership of the thermal battery unit during the lease term, after which the customer has the option to buy it or send it back.
Cache launched in 2022. For its first few years, space heating was a sideshow. Dwivedi and his team were more focused on the technology’s potential to electrify low- and medium-temperature process heat for food, chemicals, and other types of industrial production. To that end, Cache recently conducted a pilot at a Duke Energy testing facility in North Carolina that “[hosts] several interested industrial companies,” the company said last month in a news release.
Cache still works on industrial heat, but it’s also leaning into relationships with large space heating customers, particularly those with existing hot-water or steam infrastructure such as UMN Morris. That includes the U.S. Army, which is interested in the thermal battery’s ability to provide reliable backup for military installations at risk of extended power outages.
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