The underground can be used for the temporary storage of heat or cold energy. The subsoil has a high heat capacity and also reasonably good thermal insulation properties. This offers the possibility to store large amounts of heat and cold energy over a long period, e.g. one season.

This creates a wide range of opportunities to save on energy and apply other renewable energies, such as storage of solar heat in the summer for use in the winter for space heating. Another example is the storage of cold energy from the ambient air during winter periods for cooling purposes in the following summer.

Aquifer Systems (ATES)
Open wells abstract water directly from a suitable aquifer and recharge the aquifer.
Best value where a suitable aquifer exists.

Borehole Systems (BTES)
Closed loop pipework grouted into boreholes to form an underground heat exchanger.
Suitable where no aquifers exist and multiple drilling is the most cost effective solution.