Seasonal heat storage for data center waste heat

Estimated reading time: 6 minutes · Last updated: 10 October 2026

Seasonal heat storage can hold data center waste heat produced year-round in summer and return it as usable warmth in winter by warming rock or groundwater in boreholes. Epic Systems in Verona, Wisconsin, has drilled roughly 6,100 wells 300 to 800 feet (90 to 240 meters) deep around its campus and uses waste heat from a 3.5-megawatt data center to heat about 40 buildings months later. The method relies on the fact that a few hundred feet down the ground stays close to the local yearly average (about 50°F / 10°C), so warmed rock loses heat only slowly and serves as seasonal thermal storage.

How the ground holds heat for months

Seasonal heat storage turns the ground into a slow, low-loss container. In summer, warm water from a data center is pumped through pipes in boreholes where it transfers heat to surrounding rock or to an aquifer. Rock is a poor conductor of heat, so the warmed volume loses heat only at its edges; pushed into a large enough volume, most of the input remains months later.

There is no buried tank or battery: the rock or groundwater is the storage medium. That principle explains why a pile of snow melts slower than a thin sheet of snow — shape and surface area matter. Systems in colder climates have delivered water back to the surface at temperatures commonly reported around 59°F (15°C) when recovering summer-stored heat for winter use.

Working examples: borefields and aquifers

On-site projects show the concept at building scale. Epic Systems has drilled roughly 6,100 wells 300 to 800 feet (90 to 240 meters) deep around its Verona, Wisconsin campus and channels waste heat from a 3.5-megawatt data center into that borefield to heat about 40 buildings months later. The Department of Energy reports Epic’s campus buildings use about 25% less energy than comparable buildings in the same climate.

A different approach stores heat in underground water. A complex in Bonn, Germany, has used aquifer thermal energy storage since 2009 to supply between 60% and 80% of its winter heat demand for offices, a hotel, a medical center and a data center. Those examples show two technical routes—borehole thermal energy storage and aquifer storage—each suited to different geology and project scale.

Limits: thermal saturation, distance and regulatory gaps

Borefields face a concrete physical limit: if more heat is injected in summer than recovered in winter, the warmed rock slowly grows hotter year after year and the field can no longer accept heat at the design temperature. That thermal saturation of borefields forces either more use of stored heat—preheating boiler feedwater or melting snow—or more drilling to spread the heat through greater rock volume, which raises land, equipment and capital costs.

There are additional practical limits. Stored heat sits under or beside the facility that supplied it, so users must be close by. And while modelers have shown idle or orphaned oil and gas wells could be repurposed for thermal storage, most states currently regulate wells only as oil-and-gas installations or as plugged wells; a dedicated regulatory category for heat storage does not yet exist, which complicates permitting even where the geology is usable.

Scale and the policy opportunity

Whether seasonal storage becomes widespread depends on both data-center growth and policy. Data centers used about 4.7% of the country's electricity in 2024 and Lawrence Berkeley National Lab projects that share could reach nearly 12% by 2030; in some states the data center share of electricity is already much larger, at 15.4% in North Dakota and 25.6% in Virginia. About 30% to 40% of data-center electricity use goes to cooling, which is the heat stream that could be captured and stored.

The contrast between on-campus borefields and deep geothermal plants is instructive. Google has secured 115 megawatts of geothermal power in Nevada and Meta contracted 150 megawatts from New Mexico—projects that drill for heat the Earth supplies. Storing data-center heat underground is the mirror image: the drilling and wells are similar, but the heat source is the building. No one has yet stored a data center’s heat underground at the 100- to 1,000-megawatt scales now associated with large AI campuses.

The case for and against wider adoption

The bottom line

Seasonal heat storage turns a perennial nuisance—data center waste heat—into a time-shifted resource by warming rock or groundwater and recovering that warmth months later. Campus-scale examples such as Epic Systems’ borefield and Bonn’s aquifer system show the method can reduce building energy demand and supply a large fraction of winter heat. Physical limits, notably thermal saturation, distance constraints and existing regulatory categories for wells, mean the approach suits campus and local clusters more readily than dispersed, very large facilities. Where geology and policy align, repurposing idle wells or adding borefields offers a low-carbon way to keep heat local and reduce both power and water pressures from expanding data centers.

What to watch

• 2030: check whether Lawrence Berkeley National Lab’s projection of data centers reaching nearly 12% of U.S. electricity is realised.
• Watch for state action on a streamlined permit process to allow conversion of idle oil and gas wells to thermal storage; no date has been set.
• Watch for firm proposals or pilots to reuse documented orphaned wells for seasonal heat storage; no date has been set.