Heat is a valuable resource, regardless of the season, and researchers at Kaunas University of Technology (KTU) have found that the soil under our feet can serve as an efficient thermal energy storage system.

At the heart of the concept is a ground-based heat accumulator that would store excess heat energy for availability when demand peaks, according to Tech Xplore.

"Our goal was to convert heat, which would normally dissipate into the ground as waste, into a useful energy source," explained KTU professor Dr. Tadas Ždankus. 

Conservation and loss reduction are essential components in achieving net-zero goals, where every bit of energy should be harnessed and reused where possible. 

The idea of using soil as a thermal energy storage medium grew from his research into using wind turbines to produce heat instead of electricity, the report detailed. The so-called hydraulic losses noted during their operation could instead be viewed as usable heat energy.

During tests, the research team found that while transferring this heat to buildings to lower energy usage during colder seasons, a portion of it was lost in the process. 

"The question became how to not only reduce heat loss to the ground but also store and retain it for future use," Ždankus explained.

Other studies have shown that underground thermal energy storage (UTES) can be an effective long-term option based on its high storage capacity and low cost of operation. It can help retain the hot or cold energy generated seasonally, as well as excess solar energy or waste heat from industrial processes, for long periods. 

Additionally, when located at a depth of over 32 feet, the thermal inertia of the soil provides protection from the changing climate.

One particular avenue of the KTU team's testing involved heating soil layers to the point where moisture began to evaporate, triggering a phase change in which water turned to vapor.

Should we be digging miles beneath Earth's surface? No way 👎 Definitely 👍 Depends what it's for 🤔 Depends where we do it 🗺️ Click your choice to see results and speak your mind.

"Phase change can be an efficient way to store heat. The significantly higher amount of energy can be charged into the soil," explained another KTU professor.

As vapor travels through the ground, the researchers noted, its heat energy is distributed over a wider area.

"We noticed a sharp temperature rise wherever the vapor flow reached. This means the energy is moving and can be controlled," said Ždankus.

Their research could help offset HVAC energy loads by tapping into stored thermal reserves underneath buildings. This could reduce the carbon footprint generated by heating and cooling them, which accounts for around 15% of all CO2 emissions globally.

Space and water heating make up two-thirds of home energy use, which is why more efficient heat pumps, including ground-source models, are growing in popularity.

"Our immediate goal is to integrate existing solutions, such as boreholes, piles, and other underground heat exchange technologies into a system that can benefit both industry and residential sectors," Ždankus concluded.

Join our free newsletter for weekly updates on the latest innovations improving our lives and shaping our future, and don't miss this cool list of easy ways to help yourself while helping the planet.