Geothermal deep drilling for heat pump: depth, process and costs (2025)

With deep drilling, you can permanently use the heat from the ground. It is a prerequisite for the installation of a heat pump with a geothermal probe. But how deep do you have to drill, what are the costs and what must be considered? This article provides an overview.

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What is deep geothermal drilling?

A deep geothermal well is a hole up to 100 meters deep in which geothermal probes are inserted into the ground. The heat stored in the ground can therefore be used by a heat pump. It is used to supply a single-family house with heating energy from constant geothermal energy and is part of a so-called brine-water heat pump.

How deep is drilling?

A geothermal probe may generally be drilled up to 100 meters deep without a mining permit being required. To date, drilling over 100 meters requires a permit under the Federal Mining Act, so that drilling is only carried out up to this limit.

On September 4, 2024, a Draft law from the Federal Ministry of Economics and Climate Protection decided to make drilling for geothermal probes easier. Drilling up to a depth of 400 meters should no longer fall under mining law. Instead, only the rules of water law apply. This significantly facilitates the use of geothermal energy. However, the law has not yet come into force (as of June 2024).

How warm is it at a depth of 100 meters?

At a depth of 100 meters, the ground temperature is usually between 10 and 12 degrees Celsius. This temperature remains largely constant throughout the year. As a result, a geothermal heat pump has stable conditions of 8 to 12 degrees Celsius throughout, making geothermal energy a particularly efficient and reliable heat source. In addition, the constant soil temperature in summer can be used for passive cooling — without any additional energy consumption.

How much does a geothermal deep hole for the heat pump cost?

A deep geothermal well with a heat pump costs a total of between 27,000 and 45,000 euros — including geothermal probes, drilling, installation and heat pump. Deep drilling alone costs around 8,000 to 10,000 euros, depending on drilling depth, soil conditions and region. 50 to 100 euros are usually charged per meter of drilling.

What drilling methods are there?

The flush drilling process is usually used for single-family homes, but there are various drilling methods available. The choice of method depends on depth, soil structure and local conditions.

• Flush hole (rotary flush hole): A rotating drill head crushes the rock, while a flushing liquid moves the drill bit upwards. This method is particularly efficient for loose and mixed-grained soils. It is the most frequently used process for geothermal drilling in single-family homes.
• Hammer drilling (air lift hole or imloch hammer): A pneumatic hammer smashes the rock directly into the borehole. At the same time, compressed air is used to transport the drilling material upwards. This method is particularly suitable for hard and solid rock layers.
• Dry drilling: Drilling is carried out without flushing or compressed air, usually with the aid of rotary drills or screws. This method is used less frequently because it is more technically complex in deep areas.

What is the process of deep geothermal drilling?

The process of deep geothermal drilling follows a clearly structured plan so that the geothermal probes are securely and professionally anchored in the ground. After preparation, the actual drilling begins, followed by installation and connection to the heat pump.

1. Space clearance and construction site installation: The drilling area is being prepared, equipment is delivered and work surfaces are cleared.
2. Defining and measuring the drilling points: The exact position of the geothermal probes is measured and marked — taking into account the minimum distances.
3. Setting up the drilling rig and starting the drilling: Depending on the process, the appropriate drilling rig is set up and drilling is started.
4. Drilling progress with continuous flushing or compressed air: The borehole is sunk by the meter, the drilling material is transported upwards and documented.
5. Insert the earth probe into the borehole: After reaching the planned depth, the geothermal probe is inserted into the borehole.
6. Compression with heat transfer material (e.g. cement-bentonite mixture): The probe is pressed with a thermally conductive and sealing material.
7. Tightness testing and connection to brine lines: The installed probes are tested for tightness and connected to the heat pump.
8. Dismantling the construction site: After completion of the work, the drilling site will be filled again and the area will be dismantled.

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How long does it take to drill?

Deep drilling for a geothermal heat pump usually takes one to two days per well. The exact duration depends on drilling depth, soil structure and weather conditions. When drilling two holes for a single-family house, the work is usually completed within a week.

Can I drill on any plot of land?

Deep drilling for geothermal energy is not allowed on every plot of land. Whether drilling is allowed depends on local conditions such as water protection areas, soil structure and regulatory requirements. Expert testing and approval by the responsible water authority is therefore always required.

Which permits are required?

For deep geothermal drilling, the project must be notified to the lower water authority at least one month before the start. This checks whether drilling is permitted on the property. From a depth of over 100 meters, an additional permit from the State Geological Office is required — which is avoided in single-family and multi-family houses.

In which regions of Germany can deep drilling take place?

Deep drilling for geothermal energy is generally possible throughout Germany, provided that there are no water law or geological restrictions. The decision lies with the competent water authority, which reviews the project on a case-by-case basis. Regions with permeable soil structures and without water protection requirements are particularly suitable.

What do I have to pay attention to when drilling a geothermal energy well?

The following points are crucial for the successful implementation of a geothermal well:

• Check soil conditions: The surface must be suitable for drilling. Geological reports or drilling archives provide information about the structure and rock layers.
• Get approval: Before you start, the project must be reported to the lower water authority. Additional permits are required in water protection areas or at depths of over 100 meters.
• Accessibility: The drilling rig requires sufficient space and free access. Narrow access roads, slopes or buildings can make implementation difficult or expensive.
• Define drilling depth and number of holes: The required heating capacity determines how deep and how often to drill. For single-family homes, 1 to 2 holes of up to 100 meters are usually sufficient.
• Certified earthworks company: Only specialist companies with appropriate approval and experience should carry out the work. Quality and documentation are decisive for subsequent operational safety.
• insurance: The contracted earthworks company should have adequate business liability insurance. This ensures that it adheres to possible damage caused by the borehole — such as pipes or groundwater.

What complications can arise when drilling a deep hole?

Deep drilling for a geothermal heat pump can result in unexpected underground complications despite careful planning. These risks should be known in advance and considered when selecting the drilling company:

• Groundwater under pressure: If a groundwater layer is drilled at high pressure during drilling, uncontrolled water leakage and damage can occur. This also makes it difficult to securely compress the borehole with a sealing compound, which is intended to prevent surface water from entering the groundwater.
• Collapse of underground cavities: In some regions, particularly in former mining areas, drilling can destabilize underground cavities. This can lead to reductions in the surface, which impair the function and efficiency of the heat pump.
• Porous subsoil with fractures or karst water deposits: In such geological formations, the compression material used can seep away uncontrollably. This makes it difficult to properly seal the borehole or even makes it impossible.
• Mineralization and gas resources: In certain areas, groundwater may contain high amounts of dissolved minerals or carbon dioxide. CO2 leakage during drilling is a rare but serious risk that should be covered by borehole insurance.

What are the advantages and disadvantages of deep geothermal drilling?

Deep geothermal drilling offers high efficiency, a constant heat source and low space requirements, but requires high initial investments and a permit. The advantages lie in reliable energy generation in all weathers and a long service life. Disadvantages include the high costs of drilling and installation as well as possible geological restrictions on the property.

What alternatives to deep geothermal drilling are there?

Alternatives to deep geothermal drilling include area collectors, well systems (groundwater heat pumps) and air-water heat pumps. While geothermal probes are drilled vertically into the depths, area collectors use near-surface geothermal energy in horizontal pipe systems. Well systems use groundwater as a heat source. Air-water heat pumps, on the other hand, obtain energy directly from the ambient air. The best solution depends on property, water availability, regulations, and budget.