This small city in rural northeastern South Dakota has become an energy hub for the entire Great Plains region, and that reputation has been greatly enhanced by the completion of the largest energy storage project in the world.
In a groundbreaking project, South Dakota-based POET has partnered with California-based Antora Energy to launch a thermal energy storage system near POET’s ethanol plant in Big Stone City.
The 5 GWh thermal energy storage facility will absorb excess low-cost energy generated by wind turbines that may be lost due to capacity constraints on the existing grid and store it in carbon blocks for use when needed.
Officials say the new technology will be a major boost to South Dakota’s economy and environment, while also pioneering the use of new energy technologies across the country and around the world.
Developers cite potential benefits
Leaders of both companies told NewsWatch in exclusive interviews that the storage facility, the first in commercial production in Antora, will provide South Dakota with multiple benefits now and into the future, including:
1. The facility will increase the efficiency and production of POET’s ethanol plant in Big Stone City by providing a reliable source of sustainable energy during periods of peak and off-peak electricity demand, ultimately reducing the cost for consumers to purchase ethanol at the gas station.
2. It will increase production opportunities for South Dakota corn growers, who will see an expanded market for converting the grain into ethanol.
3. It will reduce dependence on fossil fuels by storing more energy generated from wind, solar or other sustainable sources.
4. The construction and development of the plant will create 300 new construction jobs in South Dakota and California and will create new full-time jobs in the Big Rock area.
“They’re taking advantage of excess wind energy that’s not connected to the grid and would otherwise be wasted, and they’re capturing that,” said Jeff Lautt, president and chief operating officer of POET in Sioux Falls, the world’s largest ethanol producer.
“No one can control the wind, so it can blow wherever it wants, but it has to meet a steady demand for power, and this system will meet that demand.”
Antora Energy CEO Andrew Ponec would not share the total cost of the project. But a press release about the storage project noted that Antora “has brought hundreds of millions of dollars in private investment to the company.”
Poneke said much of the cost of the Big Stone project was paid for through private financing led by Australia’s Grok Ventures, rather than the U.S. government. But he added that thermal storage has strong bipartisan support, including the Big Beautiful Act passed by Congress in 2025.
A May 19 press release from POET and Antora on the project 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 demand for energy continues to grow year after year, so the more energy we can get domestically, the better,” Lowndes said in the release. “This project in Big Rock will have a real economic impact for South Dakota while also creating jobs and boosting our domestic energy production.”
Regional power center located in a small town
Ponec said Big Stone City was selected as the site for Antora’s first large-scale thermal energy storage system because of its existing POET biofuels plant and Otter Trail Power Co. plant, and because the city is a major hub for the Midcontinent Independent System Operator (MISO) regional grid system.
“We are an energy technology company, so we will go where the energy users are concentrated,” he said.
Thermal energy storage captures low-cost, off-peak energy from virtually any source (in this case, local wind turbines) and stores it as heat in insulating solid blocks of carbon at temperatures up to 4,000 degrees Fahrenheit. The heat can be stored until needed and then transferred to the oil so that it can be delivered to an industrial user, in this case the POET plant next door.
There, the heat is converted into steam to power boilers, stills and other machinery used to produce ethanol and other by-products produced by POET plants. Lautt said the Big Stone plant produces 92 million gallons of ethanol annually.
Poneke likened the heat-storage process, which consists of dozens of large white metal boxes on the ground, to the operation of a giant toaster. Electricity from the outlet (energy from the wind tower) is transferred to the toaster heating coil (carbon block), which then produces heat to brown the bread (running the machinery in the ethanol plant.)
The project uses very little water and does not produce any significant emissions, Bonek said.
To illustrate the flexibility of thermal storage, Poneck noted that the Big Stone facility was built in less than a year. The facility already supplies power to POET’s factory and is expected to be fully online in October.
Another way to store energy in South Dakota
Thermal energy storage is similar to lithium-ion energy storage in that both concepts aim to capture electricity that can be retained until demand rises and potentially exceeds supply, thus stabilizing the grid and reducing costs for consumers.
While lithium batteries can only actually store electricity for a few hours, thermal storage stores energy in the form of heat and can store it for longer periods of time, Bonek said.
South Dakota may soon be home to two lithium battery projects, including in Coddington and Brookings counties, that supporters say will create new opportunities for wind and solar energy production in the state.
Lautt said Antora makes money by selling energy to POET, while opening the door to greater sustainable electricity production in the region and lower electricity costs for ethanol plants.
“It creates more efficiency for us, so we use less natural gas to operate the facility, which makes us more environmentally friendly,” he said. “It really creates a win-win across the entire footprint.”
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This story was originally published on South Dakota News Watch and distributed in partnership with The Associated Press.
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