Construction and operation of geothermal systems
Near-surface geothermal energy refers to geothermal systems with a drilling depth of up to 400 metres.
When utilising near-surface geothermal energy, a distinction is made between two different systems, the open and the closed system.
In a closed system, heat is extracted via a heat exchanger in the form of a pipe system directly in the ground. The best-known types of closed systems include vertical geothermal probes and horizontal geothermal collectors, whereby vertical geothermal probes with a depth of usually 70 to 150 metres are the most common geothermal systems. In an open system, groundwater is extracted from a production well and reintroduced via an infiltration well after the heat has been extracted. Open systems are the exception in urban areas due to the maintenance effort and the problems associated with direct intervention in the groundwater.
If the geothermal probe system is properly and adequately dimensioned, the energy stored underground can be used for heating, hot water and cooling. The background to this is the fact that the temperature in Europe increases by an average of 3 Kelvin per 100 m with depth[1].
The earth excavations associated with the installation of a geothermal probe system are generally subject to notification[2], [3].
Furthermore, both the construction of a geothermal probe system and its operation also constitute water utilisation for which a permit under water law is required[4], [5].
The application for geothermal systems is usually submitted by the company carrying out the work - as is the case for most other ground excavations. To simplify the procedure, the inter-authority portal ELBA.SAX is available for submitting drilling notifications in the Free State of Saxony. [6]
When selecting a drilling company, a certificate in accordance with DVGW worksheet W 120-2 or comparable proof of special expertise must be ensured[7].
In any case, proper drainage of the groundwater blown out during drilling must be ensured, which can sometimes occur in considerable quantities. Infiltration on your own property is rarely possible. Therefore, discharging the drilling wastewater into the public wastewater facilities of the City of Chemnitz is often the only option for regulated discharge. However, this requires prior authorisation from the waste management company of the City of Chemnitz (ESC)[8]. It is therefore recommended to obtain this prior to applying for a water permit.