A "discussion diagram" used for planning eco-neighbourhoods and showing potential  points of entry for  geothermal heat (2011). © BRGM

The different geothermal applications

Geothermal energy, produced from the natural heat of the Earth itself, is a renewable source of energy with multiple applications, from heat pumps to power production.

Geothermal energy is derived from the Earth’s natural heat, which increases with depth. It has two main applications:

  • heat production (via heat pumps or by direct heat exchange),
  • power production (via steam turbines).

Geothermal energy can be used in many ways:  for urban heating via heat networks, to heat individual houses, swimming pools and greenhouses, for industrial uses, for heating via heat pumps or for power production.

Geothermal applications for domestic and tertiary uses

Near-surface geothermal energy, known as “very low enthalpy” energy, is produced by extracting heat (at a maximum of 40°C) from the subsoil or in near-surface aquifers at depths of a few metres to 200-300 metres.

These applications can be used for heating, cooling and producing domestic hot water in individual housing, but also in the tertiary sector and in collective housing.

Direct use of geothermal heat for district heating networks

At greater depths (1000 – 2000 metres), the temperature of aquifers is in the range of 50 to 80°C. Geothermal heat extraction at these temperatures (“low-enthalpy”) involves double-flows systems: the water abstracted from the water table flows through a heat exchanger and is then re-injected.

A number of district heating networks in France are operating on this principle, for example in the Greater Paris area where 180 000 housing units are heated by low-enthalpy geothermal technology.

Power production

Power production is a “high-enthalpy” geothermal application which involves extracting heat from subsurface areas at temperatures reaching 200 to 250 °C.

The volcanic islands in overseas France are a special case: here, such temperatures occur at depths of just a few hundred metres, while the cost price of other sources of energy is significantly higher than in mainland France.

Géothermie Bouillante, a BRGM subsidiary, specialises in developing power supplies from geothermal energy in Guadeloupe and the Caribbean region as a whole.

Geothermal energy for the future

Stimulated Geothermal Systems technology (SGS) has been developed to extract geothermal heat from naturally fractured rock formations deep underground. At Soultz-sous-Forêts (Alsace), a scientific pilot, the only of its kind in the world, is testing power production by SGS. Several SGS projects are currently under way to extract heat from shallower layers for combined heat and power production (CHP).

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