A revolutionary clean energy concept, once shelved, is making a powerful comeback in the US, promising to slash heating and cooling costs and emissions! For decades, the idea of using underground aquifers as massive thermal batteries seemed like a futuristic dream. But now, nearly half a century after its initial exploration, this ingenious technology is poised to transform how we heat and cool our homes and businesses.
Back in the 1970s, the U.S. Department of Energy embarked on an ambitious clean energy experiment beneath the University of Minnesota. Their goal? To harness the earth's stable underground temperatures by storing excess heat from the summer months in an aquifer, located over 100 meters below the surface, for use during the chilly winters. This concept, known as seasonal thermal energy storage, aimed to significantly reduce our reliance on traditional energy sources.
Fast forward to today, and this groundbreaking idea is no longer just an experiment. A mere 10 miles from where those first test wells were drilled, a new, large-scale aquifer thermal energy system is being constructed. This innovative project is part of The Heights, a vibrant mixed-use development taking shape on a former golf course on the city's Greater East Side. It's set to serve 850 homes and several light-industrial buildings, drawing groundwater from wells spread across the development. This water will then be channeled through high-efficiency electric heat pumps, partially powered by solar panels, to provide remarkably low-cost heating and cooling with minimal greenhouse gas emissions.
But here's where it gets truly fascinating: This groundwater system acts as a 'thermal battery.' During the summer, excess heat can be stored underground, effectively 'charging' the aquifer. Then, in the winter, this stored warmth can be retrieved to heat the buildings. Michael Ahern, senior vice-president for system development at Ever-Green Energy, the firm behind the design, highlighted this dual capability.
This development marks one of the first large-scale aquifer thermal energy projects in the US since the Department of Energy's field tests in the 1980s. While the U.S. has been slower to adopt this technology, over 3,000 similar systems are already operational worldwide, with the vast majority located in the Netherlands, according to a 2024 study.
Marc Hoyer, a retired scientist who was involved in the original St. Paul project in the 1980s, remembers the dedication of the team. He and his colleagues would take turns sleeping in a trailer next to the wells, meticulously recording temperature and pressure readings every hour to monitor the system's performance. A federal report from 1991 concluded that seasonal storage promised to "significantly reduce the need to generate primary energy in the United States," identifying aquifers as the "most cost-effective approach."
Hoyer, now 82, expressed his delight that the technology is finally gaining traction in the U.S. "I figured nobody cared about it," he admitted, reflecting on the long wait.
'The LED of heating and cooling'
When compared to conventional methods, aquifer thermal energy storage can dramatically cut greenhouse gas emissions – by up to 74%, according to the same 2024 study. The Department of Energy likens this efficiency leap to the transition from old incandescent light bulbs to modern, energy-saving LEDs.
"This is the LED version of heating and cooling," enthusiastically stated Yu-Feng Lin, director of the Illinois Water Resources Center. He explained that while air-source heat pumps are efficient, their performance dips when outdoor temperatures become extreme. In contrast, the aquifer beneath The Heights maintains a consistent temperature of approximately 10°C year-round, regardless of Minnesota's harsh summer heat or frigid winter cold.
"Think about how much energy you are saving there," Lin urged. He also clarified a common misconception: "A lot of people think about geothermal as just hot lava [and] hot steam that pushes a turbine to generate electricity. That’s not all of geothermal."
And this is the part most people miss: By warming a portion of the aquifer with stored summer heat, winter heating becomes even more efficient. Conversely, cooling other sections with cold water in the winter reduces the energy needed for summer air conditioning. This system is similar to other geothermal networks that use rock and sediment layers, but aquifer geothermal requires significantly less drilling.
While the initial drilling for water wells can be more expensive, the overall costs are comparable. Aquifer geothermal is particularly well-suited for regions like Minnesota, which boast abundant subsurface water resources.
"It kind of makes sense to utilise that local resource," commented Rob Thornton, president and CEO of the International District Energy Association.
A Local Resource Transformed
During a site visit in late June, the former golf course was evident, with its rolling hills now slated for a sustainable future. Despite shifts in government incentives for other clean energy sources, tax credits for geothermal projects, as part of the Inflation Reduction Act, remain robust.
The total construction cost for The Heights' aquifer thermal energy system, including wells and infrastructure, is estimated at around $12 million. Federal tax credits are expected to cover about 50% of this cost, according to Ahern.
For St. Paul city council member Cheniqua Johnson, the projected savings for residents are a game-changer. "It is the difference between paying a $200 to $300 per-month bill, and less than $100," she stated, highlighting the profound impact on families struggling with utility costs. She noted that many in her community have faced utility shut-offs due to unaffordability.
Darcy Solutions, an aquifer geothermal startup, is already overseeing well drilling for a separate geothermal system at The Heights, which will serve a new service center for Xcel Energy, a major utility company. Kristine Williams, chief development officer for the Saint Paul Port Authority, sees this as a glimpse into the future of urban development.
"I think that this type of industrial development, while it’s unique today, is what we will see going forward," Williams predicted.
What do you think? Is this 'LED of heating and cooling' the answer to our energy challenges, or are there hidden drawbacks we should be considering? Share your thoughts in the comments below!
