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FG Geothermie > Geothermal energy

Unique Energy Opportunity:

Geothermal energy

The earth’s heat is a resource which is available without limit. The crust of the earth, which is 40 kilometres thick, is constantly being heated by the core, which has a temperature of almost 5000ºC. The greater the depth, the higher the temperature. Directly under the surface, the temperature is only around 10ºC – however, for every 100 metre increase in depth the temprature rises by around 3ºC. Hence at a depth of 4000 metres there are temperatures of up to 140ºC. This heat makes it possible not only to constantly provide heat energy, but also to gain electricity without any emissions. 

Various procedures have been developed in order to use the heat of the earth. FG Geothermie GmbH uses hydrothermal geothermal energy in order to generate electricity. Here hot water which is stored underground is transported to the surface. In a power plant a generator is driven through the heat, and a remote heat network is supplied. Following this the cooled water is led back into the underground water reservoir.

Where does the earth’s heat come from?

Around 4.7 billion years ago our solar system came into being. From a hot solar mist which collapsed, our sun was formed. Around 1 billion years later, our earth was formed from a collection of loose material which agglomerated through gravitation, thereby forming our early earth.

Innerer Aufbau der Erde

Another 1 billion years later, the surface temperature of the earth had sunk to less than 100°C. The crust of the earth solidified and an atmosphere containing oxygen came about. Hence 500 million years ago the conditions for life on earth were created. Today, over 99% of our planet is still hotter than 1000°C – a huge geothermal energy store. Using this energy was always a dream of humankind. Today this dream is reality.


  • Heat supply for buildings 
  • Local and remote heat supply (public buildings, larger settlements, industrial or commercial areas)
  • Electricity generation 
  • Thermal baths 
  • Cooling of buildings and industrial plants through transformation of heat into coldness, e.g. through absorption or adsorption refrigerators 


  • Geothermal energy is the heat energy which is stored underneath the solid surface of the earth.
  • The temperature of the earth’s mantle increases with increasing depth, in Germany on average by 30°C for every 1000 m increase in depth.
  • Geothermal energy can be used as a renewable energy source to generate heat and electricity.
seismic profile
Using vibration vehicles, sound waves are sent down into the depths. These waves are reflected in various ways by stone layers and are recorded by so-called geophones. In this way a detailed underground seismic profile is gained.
seismic vibration vehicles
The seismic vibration vehicles send sound waves underground which are reflected differently by the individual stone layers. (Photo: Alex Heck/FWE)

The advantage of geothermal energy

The great advantage of renewable energy is that it is continuously available. According to current predictions, the power plant capacities and electricity production of sustainable sources will approximately be tripled as early as the year 2020. In the context of the electric mobility and intelligent electricity networks (“Smart Grids”), these sustainable energy sources have a great role to play.

Electricity generation

Heat generation