Geothermal energy draws hot water from below ground to produce heating and/or electricity before reinjecting the water back into the subsoil.
The hot water that comes out of the ground flows through a closed loop and releases its heat via a heat exchanger to another network, which then takes the hot water to radiators. A backup boiler system can provide additional heating when needed and can be used in cases where geothermal energy is unavailable.
Three types of geothermal energy
There are three types of geothermal energy, based on depth:
- Low-temperature resources (at a depth of between 30 and 600 metres). Water drawn at these depths requires the use of heat pumps to provide heat directly to buildings. The water can also be used to heat swimming pools and greenhouses.
- Moderate-temperature resources (between 600 and 2,500 metres). Here, the temperature (between 30 and 90°C) makes the water suitable for use in heating networks.
- High-temperature resources (below 2,500 metres). The temperature of the water at these depths is above 100°C, which is enough to generate electricity.
The benefits of geothermal energy
The French environment and energy management agency (ADEME) and the country's geological survey* (BRGM) see geothermal power as an "outstanding energy source" since it offers a whole array of advantages with virtually no drawbacks.
Geothermal energy in France
Geothermal is now France's third-largest source of renewable energy, and its leading source in Ile-de-France. It appears to have a bright future: the Grenelle Environment Forum has forecast a sixfold increase in geothermal production by 2020! However, geothermal energy, especially at greater depths, requires extremely specialised technology and expertise, which can only be provided by established professionals and specialists. This applies to the entire project chain, including operation and maintenance. Dalkia can handle every aspect of this complex approach and has established itself as France's leading name in geothermal solutions.
*Les Enjeux des Géosciences. La Géothermie - December 2004.