Underground 'Thermal Batteries': How Aquifer Energy Storage Could Cool AI Data Centers and Save Water

Researchers in the United States have put forward an innovative proposal to use underground aquifers as giant natural 'thermal batteries' to cool energy-intensive data centers, offering an unconventional solution to the growing environmental burden posed by the AI industry.

The study was led by scientists at the Illinois State Geological Survey, part of the Prairie Research Institute at the University of Illinois Urbana-Champaign (UIUC). They propose Aquifer Thermal Energy Storage (ATES) systems as an effective way to reduce the electricity consumed by cooling AI data centers.

ATES systems store seasonal thermal energy in underground groundwater, operating much like a large-scale natural thermal battery. Using 'well doublets'—pairs of wells that extract and reinject water—they provide a highly efficient, low-carbon heating and cooling solution.

'Data centers consume enormous amounts of electricity, and depending on their design, between 10% and 40% of that energy is used solely for cooling,' said postdoctoral researcher Upasana Pandey, who led the study. 'These facilities also consume vast quantities of water. Many cooling methods rely on evaporation, which means that water is permanently lost from local supplies.'

Earth's Natural 'Thermal Spring'

To prevent servers from overheating, data centers are consuming staggering amounts of electricity and water. In 2023, Google reported that cooling across all its data centers consumed more than 6 billion gallons of water. Many existing cooling systems depend on large-scale evaporation, permanently removing water from local sources.

Pandey, along with UIUC professors Dr. Yu-Feng Lin and Dr. Andrew Stumpf, argues that ATES systems offer a viable alternative by exploiting the Earth's naturally stable subsurface temperature.

The proposed system pumps cold groundwater from underground aquifers through heat exchangers inside data centers. After absorbing heat generated by computing equipment, the warmed water is reinjected into the aquifer for storage.

In colder months, the process can be reversed: heat stored underground during summer can warm buildings in winter, while cold groundwater collected in winter can be stored for summer cooling. This approach has the potential to improve cooling efficiency and reduce overall electricity demand.

Stumpf noted that regions such as Illinois can take advantage of the Earth's near-constant subsurface temperature rather than relying on energy-intensive seasonal cooling systems. 'You're no longer adjusting from 90°F down to 70°F—you're adjusting from roughly 55°F to 70°F,' he explained.

Protecting Drinking Water Supplies

Unlike most conventional cooling systems, this technology does not require potable freshwater. The research team emphasizes that deeper saline aquifers, contaminated groundwater, and even water accumulated in abandoned mines can all serve as thermal storage media.

The team believes Illinois is particularly well-suited for this application, owing to its pronounced seasonal temperature swings, abundant groundwater resources, and glacial sediment layers that conduct heat effectively when saturated.

However, the primary barrier is economic rather than technical. Geothermal cooling systems require higher upfront investment, though long-term operating costs are typically lower. The challenge is that many projects are evaluated over a 5-to-10-year payback window, rather than the 20-to-40-year lifespan over which these systems deliver their greatest value.

The team notes that the workforce skills needed to deploy these systems already exist, as much of the required drilling expertise is common in the oil, gas, and water-well industries.

'In this context, water is a remarkable substance because of its high heat capacity and its ability to act as an excellent thermal carrier when in motion,' said Yu-Feng Lin in a statement. 'That combination is exceptionally rare, and in groundwater, we can harness those same properties to store energy.'

The research has been published in the academic journal Groundwater.

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