Why geothermal energy?Where does it come from?
Geothermal energy originates from the center of the earth, where temperatures are as high as 2.000 to 8.000 ˚C. The closer you get to the earth's crust, the lower the temperatures. The heat is transformed in energy. The outer 6 kilometers of the crust contains 50.000 times as much energy as all the oil and gas reserves worldwide.
How does it work?
Geothermal energy is the use of the earth's heat for generating heat of electricity. For the installation of a geothermal plant drillings are made to deep groundwater reservoirs or aquifers. In the Netherlands these reservoirs can be found at a depth of 1.5 to 4.0 kilometers. In other countries, either deeper or shallower drillings are required depending on the geological and geothermal subsurface conditions.
To extract the water a well consisting of two bore holes is needed: one for production and one for injection. The production well pumps the water to the surface and leads it to the geothermal plant. The injection well is used to pump the cold water back into the earth. This way the water level in the reservoir remains stable. This is called a geothermal doublet.
Heating and electricity
From about 1,8 kilometers beneath the surface the aquifers in the Netherlands are hot enough to produce water of 70 ⁰C or more, which is enough to supply tap water of heating for buildings or greenhouses. From about 3 kilometers the temperatures are high enough for electricity production. As a consequence of the heat radiating from the center of the earth, the temperature of the earth increases with 3 ⁰C every hundred meters.
The Dutch subsurface offers great opportunities for geothermal energy and the first projects have already been carried out. Important advantages are:
- The project will pay itself back within 5 to 10 years. After that, energy will be almost for free;
- Marginal CO2 emissions;
- No waste, noise or other emissions;
- Vast availability and controllability;
- Low maintenance costs.