Aquifer Thermal Energy Storage: Heat Banking Beneath Our Feet
Beneath the ports, refineries, and coastal cities that anchor the maritime economy lies an overlooked resource: the slow, steady thermal mass of groundwater. Aquifer thermal energy storage, or ATES, taps into that mass to bank heat and cold for months at a time, offering ship operators, terminal managers, and energy planners a way to cut emissions without reinventing their infrastructure. It sounds almost too simple to matter, yet it is quietly reshaping how industrial waterfront sites manage energy.
How Aquifer Thermal Energy Storage Works
At its core, aquifer thermal energy storage is a seasonal battery made of water and sand, or water and rock, sitting underground. Instead of storing electricity in chemical cells, ATES stores thermal energy directly in a natural aquifer, using the groundwater itself as the storage medium. Two or more wells are drilled into a confined or semi-confined aquifer, one designated as the warm well and another as the cold well. During summer, excess heat from a process, a building, or even a power plant’s cooling system is injected into the warm well, raising the local groundwater temperature. That heat stays put in the aquifer because groundwater moves slowly, often just meters per year, so the thermal plume doesn’t drift off and dissipate before it’s needed.
Come winter, the system reverses. Water is pumped from the warm well, passed through a heat exchanger to extract its stored warmth for space heating, and then the now-cooled water is reinjected into the cold well. In summer, the cycle flips again: water from the cold well is drawn up to provide cooling, and the warmed return water goes back into the warm well. Over successive seasons the aquifer essentially gets charged and discharged like a giant geological battery, with recovery efficiencies typically in the 70 to 90 percent range depending on aquifer characteristics, well spacing, and how well the warm and cold zones stay separated.
The technology relies on favorable hydrogeology. Operators need a permeable aquifer with low regional groundwater flow, confined by impermeable layers above and below to prevent the thermal energy from escaping vertically. Site investigation, including pump tests and groundwater modeling, is essential before any wells go in, because a poorly characterized aquifer can lead to thermal breakthrough between wells or unexpected interference with neighboring groundwater users.
Where It Fits Into the Energy and Maritime Landscape
Aquifer thermal energy storage has found its strongest foothold in the Netherlands, where thousands of systems now heat and cool offices, hospitals, greenhouses, and increasingly, industrial facilities near ports. Rotterdam, Europe’s largest port complex, has become something of a proving ground, with ATES systems integrated into harbor-adjacent developments to offset natural gas use for heating. The logic is compelling for maritime infrastructure specifically: ports and terminals already have the land footprint, the heavy equipment, and the capital appetite for long-term infrastructure investment that ATES projects demand.
Shore power installations, LNG bunkering terminals, and shipyards generate substantial waste heat from compressors, generators, and industrial processes. Rather than venting that heat to the atmosphere or dumping it into harbor waters, where it can create localized thermal pollution affecting marine ecosystems, operators can bank it underground for reuse. Wärtsilä and other marine power technology providers have highlighted ATES as a complementary piece to hybrid and electrified port operations, where reducing fossil fuel demand for ancillary heating and cooling loads supports broader decarbonization targets. District heating networks serving coastal communities have also paired ATES with combined heat and power plants, using the aquifer to smooth out the mismatch between when heat is produced and when it’s actually needed.
Challenges and the Road Ahead
ATES is not without friction. Permitting can be slow, since regulators must ensure thermal injection doesn’t degrade groundwater quality or trigger disputes with neighboring water rights holders. Upfront drilling costs are substantial, and the economics only pencil out over long operating horizons, typically fifteen to twenty years, which can be a hard sell for operators accustomed to shorter payback expectations. There’s also a geographic constraint: not every port or industrial site sits atop a suitable aquifer, and comprehensive subsurface mapping is still catching up with demand in many regions outside northern Europe.
Even so, as ports chase net-zero targets and electricity grids strain under rising cooling and heating demand, aquifer thermal energy storage offers a rare combination of mature technology and untapped potential. Expect to see more maritime hubs following Rotterdam’s lead, treating the ground beneath their terminals as seriously as the water beside them.
