Electricity and heating from deep geothermal energy


Deep under the ground, there is an abundant amount of energy in the form of heat. Deep geothermal technologies make it possible to exploit it for industrial and non-industrial purposes. Find out more!

Image Copyright: BMWi

Drilling for deep geothermal energy

© BMWi

Geothermal plants use heat stored in the Earth's crust for heating, cooling and generating electricity.

The reservoirs of geothermal energy are greater deep within the Earth than at the surface. Wells up to 5,000 metres deep are drilled into these underground heat sources. The effort is worth it because the temperature is also much higher the further down you go.

Geothermal heat can be used to profitably produce environmentally friendly electricity as of about 90 degrees Celsius. Across the globe, plants for generating electricity from geothermal energy have been installed with a total capacity of 12.6 gigawatts – with 26 megawatts of this capacity in Germany (see IRENA). More frequently, geothermal energy is used to supply heat. The heat generated from deep geothermal energy is enough to supply entire urban districts with heat.

A key benefit of this particular source of energy over other types of renewable energy is its constant availability. This makes geothermal energy a useful complement to wind energy, for example, which is weather-dependent.

The German geothermal sector offers the entire spectrum of technology – from hydrothermal to petrothermal and deep geothermal energy.

How it works: Closed and open systems

Image Copyright: BGR Hannover

Drilling rig for deep geothermal drilling

© BGR Hannover

Geothermal systems can be designed as an open or closed system. Closed systems are often used in near-surface areas and open systems are commonly used for deep geothermal applications. At the surface the heated medium can be used for heating and for electricity generation.

In an open system hot water is extracted from an underground aquifer and pumped to the surface, where the heat is transferred to a heat exchanger. The cooled off water is then pumped back into the aquifer and the cycle starts over again. Other types of open systems like the hot dry rock technique pump a heat carrier under pressure into hot rock layers. The heat carrier absorbs the heat of the rock formation and is pumped back to the surface

In closed systems the heat carrier medium circulates through a closed pipe system. The pipe has a high heat permeability to facilitate the heat transfer between the subterranean earth layers to the heat carrier in the pipe system.

A closer look: Three forms of geothermal systems

Based on the availability of deep water, water permeability and the system concept, a distinction can be made between hydrothermal and petrothermal geothermal energy as well as deep borehole heat exchangers

Petrothermal applications: Petrothermal geothermal energy comes from deep-lying heat reservoirs, which have no water flow or only negligible water flow, such as dry layers of rock with temperatures of more than 150°. Through an injection borehole, water is transferred under the earth for heating.

Hydrothermal applications: Hydrothermal applications tap into already existing hot water reservoirs some 400 meters below the surface. In this case, the hot water is used for driving a steam turbine to create electricity and heat simultaneously.

Borehole heat applications: Deep borehole heat exchange technology refers to a closed system of energy production comprising a single borehole at depths of 400 m to several thousand meters. Water circulates through double pipe exchangers in a closed circuit. The heat from the water heated at these depths is then extracted at the surface and delivered to a heat pump circuit. In the case of high temperatures, the recovered energy can be used, for example, as process heat for industrial applications or for agricultural applications in the case of low temperatures. .