More than 200 carbon blocks — each glowing at temperatures that dwarf a blast furnace — are now sitting on an empty lot beside a South Dakota ethanol plant, storing wind energy that would otherwise go to waste. Antora Energy says the system, a 5-gigawatt-hour thermal battery, is the largest of its kind in the world.
But experts say the most consequential part of what Antora has built may not be visible from the outside at all.
A 5-gigawatt-hour system unlike anything built before
Antora’s system works on a principle that’s almost disarmingly simple. Clean electricity flows through resistance heaters that warm solid carbon blocks to temperatures approaching 2,400°C — far hotter than a steelmaking furnace — where the heat can be held for days at a time. When the neighboring ethanol plant needs energy, the system pipes steam directly over the fence. Poet’s bioprocessing facility uses that steam to convert corn into ethanol, a process that currently draws heat from boilers inside a 475-megawatt coal plant that Otter Tail Power operates next door.
The Big Stone City project is roughly 1,000 times larger than Antora’s earlier proof-of-concept — a 5-megawatt-hour pilot launched in late 2023 at a Wellhead Electric facility near Fresno, California. Chief operating officer and co-founder Justin Briggs said the entire system was built in under a year, a timeline he described as a deliberate effort to demonstrate how quickly the technology can be deployed at scale.
Why industrial heat is a stubborn decarbonization problem
Heat is easy to overlook in conversations about clean energy. Electricity gets the headlines; heat runs the factories. Industrial heat use accounts for roughly 12% of U.S. greenhouse gas emissions — a share that receives far less policy attention than power generation or transportation.
Systems from companies including Antora, Rondo Energy, Brenmiller Energy, and Electrified Thermal Solutions can reach temperatures at or above 750°C. A 2023 report by The Brattle Group found that threshold is sufficient to meet nearly 75% of all U.S. industrial heat demand. The technical case for thermal batteries is increasingly solid. The commercial case is another matter entirely — utility rate structures in the United States have remained one of the sector’s most persistent obstacles, rewarding neither flexibility nor the ability to absorb surplus renewable power.
The tariff that might matter more than the technology
Working with Otter Tail Power, Antora developed what they call a “thermal market energy pricing rider” — a voluntary tariff that links Antora’s electricity consumption to periods when local renewable generation is producing more power than the grid can use.
Noah Long, Antora’s director of state and regulatory affairs, describes traditional utility rates as spreading costs like peanut butter: evenly across all customers, regardless of when or how flexibly they draw power. The new tariff corrects this by pairing Antora’s charging schedule with surplus renewable availability. The two companies exchange day-ahead data on expected electricity needs and pricing — a structure that mirrors how wholesale electricity markets already operate. Regulators in Minnesota, North Dakota, and South Dakota have all approved it. California is now considering similar legislation.
Protecting the grid — and everyone’s electricity bill
One of the tariff’s most important provisions addresses who pays for grid upgrades. Under the Otter Tail arrangement, the answer is unambiguous — the large customer does. Antora funded construction of a 34.5-kilovolt transmission line to connect its system to the grid, ensuring those costs weren’t distributed across other ratepayers.
Francesco Aimone, an industrial electrification senior fellow at the Center for Climate and Energy Solutions, describes this emphasis on using existing grid infrastructure and intermittent energy as critical. Flexible loads that charge when power is cheap and abundant are, he argues, central to preventing electricity bill increases for households and small businesses.
What comes next for thermal energy storage
Antora raised $150 million in 2024 and has since expanded its San Jose manufacturing facility into a three-building campus. The Big Stone City project is jointly owned by Antora and Australian investment fund Grok Ventures, with heat sold to Poet under a long-term offtake agreement — a structure that could serve as a template for future installations.
Melissa Hulting, director for industrial decarbonization at C2ES, said the project adds a meaningful proof point for thermal batteries in real commercial settings. She was direct, though, about where the more transferable lesson lies: “The distinguishing factor is the tariff.”
If utilities across the United States adopt similar rate structures, thermal batteries could move from an emerging technology into a mainstream decarbonization tool — serving not just ethanol plants but breweries, cement producers, chemical facilities, and any other industry that runs on heat.
Carlos is an engineer with strong expertise in technical and industrial topics. He previously worked at international companies such as Siemens and speaks Spanish, German, English, and Italian.
