The thermal energy storage facility in Big Stone City, S.D., at top center, under construction in October 2025. (Bart Pfankuch/South Dakota News Watch via AP)
BIG STONE CITY, S.D. (AP) – This small city in rural northeastern South Dakota has established itself as an energy hub for the entire Great Plains region, and that reputation has received a big boost by landing what will be among the world’s largest energy storage projects.
In a groundbreaking project, South Dakota-based POET has partnered with Antora Energy of California to launch a thermal energy storage system adjacent to POET’s ethanol plant in Big Stone City.
The 5 gigawatt-hour thermal energy storage facility will absorb excess, low-cost energy from wind turbines that might otherwise be lost due to capacity limits on the existing power grid and store it in carbon blocks for use when needed.
Officials said the new technology will be a major economic and environmental boost to South Dakota while also pioneering the use of a new energy technology for potential use across the country and the world.
Developers cite potential benefits
Leaders of the two companies told News Watch in exclusive interviews that the storage facility – the first to be put in commercial production by Antora – will generate several benefits now and well into the future for South Dakota, including:
1. The facility will improve efficiency and increase outputs at POET’s ethanol plant in Big Stone City by providing a reliable source of sustainable energy both during times of peak and non-peak power demand, ultimately reducing consumer costs for ethanol at the gas pump.
2. It will increase production opportunities for South Dakota corn growers, who will see expanded markets for their grains to be converted into ethanol.
3. It will reduce reliance on fossil fuels by enabling greater storage of energy generated by wind, solar or other sustainable sources.
4. Construction and development of the plant has supported 300 new construction jobs in South Dakota and California and will generate new full-time employment in the Big Stone City area.
“They’re taking excess wind energy that doesn’t have a home on the grid and otherwise would be wasted, and they’re capturing that,” said Jeff Lautt, president and chief operating officer of POET in Sioux Falls, the world’s largest producer of ethanol.
“Nobody’s got a switch for the wind, so it blows when it wants to blow, yet there’s a steady demand for power that has to be met, and this system will provide for that.”
Andrew Ponec, chief executive officer of Antora Energy, was unwilling to share the total cost of the project. But a press release on the storage project noted that Antora has “catalyzed hundreds of millions in private investment in the company.”
Ponec said the majority of costs for the Big Stone project were paid through private financing, led by Grok Ventures of Australia, and not the U.S. government. He added, however, that thermal storage has received strong bipartisan support, including in the Big Beautiful Bill passed by Congress in 2025.
A May 19 press release on the project from POET and Antora included statements of support from U.S. Sens. John Thune and Mike Rounds, U.S. Rep. Dusty Johnson and South Dakota Gov. Larry Rhoden.
“America’s need for energy is continuing to rise year after year, (so) the more of that energy we can take right here at home, the better,” Rounds said in the release. ”(This) project in Big Stone City will have a real economic impact in South Dakota while also creating jobs and boosting our domestic energy production.”
A regional power hub set in a small town
Big Stone City was selected as the site for Antora’s first large-scale thermal energy storage system because of the existing POET biofuels plant and the Otter Trail Power Co. plant on the site, and due to the city’s location as a major hub on the regional Midcontinent Independent System Operator (MISO) power grid system, Ponec said.
“We’re an energy technology company, so we’re going to go to wherever there are big concentrations of energy users,” he said.
Thermal energy storage collects low-cost, off-peak energy from virtually any source – local wind turbines in this case – and stores it as heat in insulated blocks of solid carbon that reach 4,000 degrees Fahrenheit. The heat, which can be stored until needed, is then transferred into an oil that allows it to be carried to industrial users, in this instance the POET plant next door.
There, the heat is transferred to steam that powers boilers, distillers and other machinery used in production of ethanol and a host of other byproducts generated at the POET plant. The Big Stone plant produces 92 million gallons of ethanol annually, Lautt said.
Ponec likened the thermal storage process – which consists of dozens of large white metal boxes on the ground – to the operations of a giant toaster. Electricity from the outlet (energy from wind towers) is transferred to the toaster heating coils (the carbon blocks), which then generates heat to brown the bread (run machinery in the ethanol plant.)
The project uses very little water and does not create any substantial emissions, Ponec said.
To illustrate the nimble nature of thermal storage, Ponec noted that the Big Stone facility was built in less than a year. The facility is already providing power to POET’s plant and should be fully online in October.
Another type of energy storage for South Dakota
Thermal energy storage is similar to lithium ion energy storage in that both concepts seek to capture power that can be held until demand goes up and may exceed supply, thereby stabilizing the power grid and reducing costs for consumers.
But while lithium batteries store actual electricity and only for a few hours, thermal storage holds the energy as heat and can hold it for much longer periods, Ponec said.
South Dakota might soon be home to a pair of lithium battery projects, including in Codington and Brookings counties, which backers said will create new opportunities for wind and solar production in the state.
Antora makes money on the project by selling its energy to POET while opening the door to greater sustainable electricity production in the region and lowering power costs for the ethanol plant, Lautt said.
“It creates more efficiency for us, so we’re then using less natural gas to operate the facility, which makes us greener,” he said. “It really creates a win-win-win all across the footprint.”
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