Geothermal Energy Utilization

A geothermal probe is a heat exchanger that extends vertically deep into the ground, through which a heat-transfer fluid circulates and absorbs heat.

From a geological perspective, the Fulda district is considered a sensitive area for the installation of geothermal probes; therefore, a (fee-based) expert assessment—for example, by the Hessian State Office for Nature Conservation, Environment, and Geology—is regularly conducted to determine under what conditions and requirements the system may be installed. Upon submission of a declaration of cost coverage, the expert opinion can be obtained as part of the permitting process.

Only a specialized company is permitted to install the system. The company must be certified in accordance with DVGW W 120-2. In some cases, additional authorities must give their approval. This applies particularly to boreholes deeper than 100 meters. Additional costs may also arise. For large systems, a test borehole is often required first. This must be approved and inspected. Systems in commercial or public settings are subject to a special requirement: an expert must inspect them regularly. This is mandated by the regulation governing water-polluting substances.

For more information, please contact the Hessian State Office for Nature Conservation, Environment, and Geology and the Hessian Ministry of Agriculture and Environment, Viticulture, Forestry, Hunting, and Regional Affairs:

Geothermal collectors are flat pipe systems that are laid horizontally in the ground. A mixture of water and antifreeze circulates through these pipes. They harness the thermal energy radiated by the sun into the ground.

Outside of drinking water and medicinal spring protection areas, a facility may generally be constructed to a depth of up to 4 meters under a notification procedure. A permit under water law is not required in such cases.

If groundwater is tapped during construction—even at a shallow depth—this must also be reported immediately.

If the systems are located within a drinking water or medicinal spring protection zone, or if the collectors are less than 1 m above the highest groundwater level, there is a risk of adverse effects on the groundwater (due to extensive soil disturbance, heat extraction, and the use of heat transfer fluids that pose a risk to water quality). The same applies to a high spatial concentration of systems. In such cases, a permit under water law may be required.

To generate heat, several wells are drilled and a so-called water-to-water heat pump system is installed. Installation typically requires several more extensive ground investigations. Heat is extracted directly from the groundwater.

Because of the extraction and reinjection of groundwater—and the potential risks this poses—these facilities are subject to permitting under water law. The permitting process is based on the guidelines for geothermal probes.