Underground Thermal Energy Storage (UTES)

About UTES

Underground Thermal Energy Storage (UTES) is the concept of storing excess heat in the ground in the summer, to then be extracted in the winter. Renewable energy sources such as solar thermal produce most of their heat when it is not required and hence, it is wasted. For this reason, it is becoming increasingly common to use integrated seasonal heat storage to improve the total system efficiency.

Energy Concept

An Underground Thermal Energy Storage (UTES) system is ideal for systems with at least a 100kW energy requirement (predominantly heat) and a storage volume of >10,000m³.

The three main components of the system are:

  • Heat Source (e.g. solar thermal, solar absorbers or industrial waste heat)
  • Borehole Thermal Energy Storage (BTES) – the method of storing the energy
  • Heat Distribution, typically via a district heating network

Heat Storage in Probes

A borehole thermal energy storage (BTES) probe field differs from standard ground-source boreholes, as the main objective is to store heat effectively. The design is therefore based around these key considerations:

  • Installation depth typically 30-50m
  • No groundwater flow
  • Probe spacing 3-4m (normally 6m)
  • Insulation above the probes to reduce heat losses

RAUGEO PE-Xa probes are the only ground source probes suitable up to 95°C.


  • High temperature resistance up to 95°C
  • Jointless probe tip offers the highest reliability
  • Excellent resistance to point loads and notches & grooves
  • Uses the leak-proof REHAU EVERLOCTM jointing system
  • 10-year consequential loss warranty for every PE-Xa probe installed