Seasonal geothermal storage for large areas and districts
Geothermal probes not only extract energy, but can also store it for future use by putting heat into the ground and withdrawing it later. The denser the placement of geothermal probes, the more efficient the storage becomes, reaching an efficiency of up to 70 %. There already exist several such storage systems in Switzerland.
On the Hönggerberg campus of ETH Zurich, 425 geothermal probes store waste heat from server rooms and laboratories 200 meters below the surface (read more here). The concept of seasonal storage with geothermal probe fields is ideal when built underneath new building developments.
On the contrary, the Paris Basin has shown us for many years how an existing urban area can reach independency on oil and gas. Warm water from a water-bearing layer is pumped to the surface and fed through a heat exchanger, thereby supplying heat for a district heating system. Afterwards, the cooled water is reinjected into the subsurface, where it is reheated by the earth (read more here).
Shallow rock layers may also be used for seasonal geothermal storage with moderate temperatures (up to 50 to 70 degrees Celsius), provided they have large permeability and aren’t too thick. Additionally, the ground water must not be used for drinking water and should only have low flow rates. Heat can be supplied by waste heat from industry and refuse incinerators or, hopefully in the future, by petrothermal geothermal power plants. 2500 such geothermal storage devices in the Netherlands have already been installed from 20 to 300 meters underground and are used to heat houses.
The Canton of Geneva is confident that its Molasse Basin is well suited for geothermal heat storage and hot water extraction. The Geothermie2020 project was initiated for the planning and implementation of this concept. With this in mind, the Competence Center SCCER-SoE and the University of Geneva are working together to find suitable locations through geologic analyses and simulation.
We have reached our second set of conclusions:
- Densely built cities should be analyzed to determine whether shallow water-bearing layers may be used for geothermal storage.
- New areas under construction should install geothermal probe fields for seasonal thermal storage.