The A to Z of Geothermal Energy


At Soultz-sous-Forêts  as in Maisons-Alfort in France, geothermal energy has established itself as a reliable, economical and durable source of heat generation. This technique of recovering heat from below ground level, is nevertheless still quite unknown to the general public. Used to produce – depending on the drill – heat but also electricity, geothermal energy is an important ally for the countryside. Focus on this special technique.

What is geothermal energy?

Geothermal can be summed up as consisting of three different ways to use heat from below the ground to produce heat or electricity.

  • High temperature geothermal energy (over 150 ° C) uses active geological deposits, located in volcanic areas. In this method, steam powers a turbine to generate electricity.
  • Low and medium temperature geothermal energy (between 30 and 150 ° C) draws water from depths up to 3 km using a heat pump and a heat exchanger. This is the most easily exploitable technique for heating networks.
  • Geothermal energy at very low temperatures (less than 30 ° C) recovers water at depths of tens of metres deep (sedimentary basins) through heat pumps. It is reserved for small installations, but remains the most commonly exploited technique for heat networks.


A cost-effective and clean energy


Geothermal energy is a renewable energy with low environmental impact. It powers networks through wells in which hot water rises. Heat is then transported by underground pipes. This technique generates no combustion or no emissions of greenhouse gases. It does not cause any noise pollution which might disturb nearby residents. If precautions are taken to ensure that the captured heat remains inferior to the yield of the well, geothermal energy is a completely renewable energy.


Deep geothermal energy requires a strong initial investment, due to the complexity of its installation. However, once the well is operational, its price remains constant, since there is no purchase of fuel. This makes geothermal energy an economic and stable energy which can serve several districts simultaneously. On average, geothermal plants cover 60% of the heat requirements of their users.

Geographical and technical drawbacks

In France, geothermal energy is not as developed for heating networks compared to other energy sources because it has some limitations. First, the ground must be suitable: cold rock is too hard to crack; earth with insufficient calorie content will lose its ability to grow vegetation as certain practices can cause land subsidence.


Furthermore, deep geothermal energy requires the use of a technique of fracturing the rock with water under pressure, which may cause micro-earthquakes. This hydraulic fracturing uses water, sand and chemicals.


The French landscape

Geothermal energy currently represents 30 of the 450 French heating networks. It is the most cost effective heat source in terms of cost and profit in the Paris area and in Aquitaine. This heat production technique involves nearly 200,000 homes across the Hexagon, the equivalent of 500,000 inhabitants. France has one of the largest geothermal heating to district heating networks, located in Chevilly-Larue. Created in 1985, it now serves nearly 45,000 residents.


Projects such as Val d’Europe in Villeneuve-le-Comte or new neighbourhoods on the right bank of Bordeaux show that geothermal energy is a tremendous opportunity. Under good operating conditions, it is an efficient and cost effective renewable energy model.



Image source: Flickr (Ilja Klutman)

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