Epic Systems stores data center heat in 6,100 underground wells

Researchers propose orphaned oil and gas wells for thermal storage

Epic Systems in Verona, Wisconsin, has spent two decades building an underground thermal storage system that uses waste heat from a 3.5-megawatt on-campus data center to warm about 40 buildings. The company has drilled approximately 6,100 wells, 300 to 800 feet deep, according to Moones Alamooti, an assistant professor of energy and petroleum engineering at the University of North Dakota.

The unusual element of the system is that it returns heat to the ground in summer and recovers it months later, reversing the usual pattern of ground-source heating, according to Alamooti. Water heated by the data center’s servers is pumped through pipes deep underground, warming the surrounding rock. Months later, that same water is pumped back through the pipes and returns to the surface warmer than when it left. “Rock is a poor conductor of heat, which sounds like a defect but is in fact a crucial element,” Alamooti wrote, because heat can escape only through the edges of the warmed zone, leaving most of it in place long enough to be recovered.

The temperature of the recovered heat limits what it can power. In much of Alamooti’s own research, wells are designed to turn stored heat back into electricity; in those systems, surplus solar and wind power runs a heat pump that heats material packed into the well to as much as 284°F (140°C), and that heat later drives a generator. At the temperature a data center’s servers produce — about 140°F (60°C) — the recovered heat is not enough to drive a turbine to generate electricity, but it is efficient for warmth: a heat pump can move large amounts of heat with relatively little electricity, Alamooti wrote.

At Epic, the recovered heat warms offices, supplies hot water to dining halls and melts snow off sidewalks, according to Alamooti. The data center behind the heat, however, is small: its 3.5-megawatt capacity is dwarfed by AI campuses now under construction at 100 to 1,000 megawatts, and no one has stored a data center’s heat underground at that larger scale. A different system, using underground water reserves called aquifers, has supplied 60% to 80% of the winter heat demand for a complex of offices, a hotel, a medical center and a data center in Bonn, Germany, since 2009. Borehole systems in the Netherlands surface stored heat at around 59°F (15°C), according to Alamooti.

The system faces a constraint: boreholes can overheat over time if more heat is added in summer than is withdrawn in winter, requiring the field to be expanded or the heat put to additional uses such as preheating water for boilers or melting snow, according to Alamooti. Epic has not published what the system cost. The U.S. Department of Energy has reported that Epic’s buildings use about 25% less energy than comparable buildings in the same climate.

Researchers have also proposed a different way to avoid the cost of new drilling. The U.S. has more than 141,000 documented orphaned oil and gas wells waiting to be plugged, and Alamooti and colleagues have modeled how idle wells in California — one subset of that national count — could be turned into thermal storage without replacing their existing steel casings. Most state regulatory frameworks classify a well as either an oil and gas well or a plugged one, with no category for heat storage, and Alamooti and a colleague have proposed a streamlined permit process that states could adopt to allow wells to be used for this additional purpose.

Two other limits apply, according to Alamooti. The first is distance: the stored heat sits under or beside the facility, so whoever uses it has to be close by. The second is size: Epic’s 3.5-megawatt data center is small compared to the AI campuses now being built at 100 to 1,000 megawatts, and its borefield serves the whole campus, not just the servers. No one has yet stored a data center’s heat underground at that larger scale.

The proposal comes amid rapid growth in data center electricity demand. Data centers used about 4.7% of U.S. electricity in 2024, a share the Lawrence Berkeley National Laboratory projects could reach nearly 12% by 2030, according to Alamooti. In North Dakota, where Alamooti teaches, data centers account for 15.4% of electricity consumed; in Virginia, the figure is 25.6%.

About 30% to 40% of data center electricity use goes toward cooling, with the heat escaping into the atmosphere as water used in cooling evaporates, Alamooti wrote. Making different choices about how to handle the heat “could help keep power bills down and water in local rivers” as communities push back against the sector raising local power bills and drawing on local water supplies, he added.

Google has separately contracted for 115 megawatts of geothermal power in Nevada and Meta for 150 megawatts at a geothermal plant in New Mexico — projects that drill for the Earth’s stored heat to generate electricity, rather than recycling waste heat from servers, according to Alamooti.