HOT DRY ROCK
1. Introduction
Hot springs are found in several places on earth and are used for spas, urban heating networks and to generate electricity.
The water gets hot by seeping into the ground through cracks. It is heated from contact with hot rock and flows out, still hot, in another place. Actually, the rocks in the subsoil are continually heated by the thermal flux of the earth. Consequently, the temperature increases with depth by more or less 3° every 100 m to reach 1000° 40 km under the earth's crust.
The water gets hot by seeping into the ground through cracks. It is heated from contact with hot rock and flows out, still hot, in another place. Actually, the rocks in the subsoil are continually heated by the thermal flux of the earth. Consequently, the temperature increases with depth by more or less 3° every 100 m to reach 1000° 40 km under the earth's crust.
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2. Hot Dry Rock Project
Because of the geothermy of hot rocks we live over an almost infinite store of renewable energy. And we don't have to dig very deeply to transform this heat into electricity. Often, at a depth of just 5 km, the conditions make it possible to produce this energy.What we need is in fact a "man made heat exchanger" to harvest the heat produced by the rocks. For this reason, European scientists launched an experimental geothermal energy project “Hot Dry Rock”. The experimental site of this project is located in Soultz-sous-Forêts, near Strasbourg. In Soultz we are currently drilling the third well for what we call the basic module. This basic, 3-well module could generate 5 to 6 MW of electricity.
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3. The Principle
A deep hole must be drilled to hook up with a natural network of crevices in the subsoil. Then water under pressure is injected. The water circulates in the crevices and heats in contact with the rock. When it reaches 200 ° C, it is extracted from the subsoil still under pressure via the production well. The heat from- this hot water can then be transmitted to an operational circuit. The water heats a working fluid which evaporates and turns a turbine. In addition, the heat loss can still be used for urban heating systems or a source of industrial heat.
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4. Conclusion
In the future, a 25 MW industrial prototype will follow and, later on, a series of units based on this process. Scientists estimate that the potential of sites suitable for the exploitation of geothermal energy in Europe could generate some 110,000 MW. For the sake of example, this corresponds roughly to the amount of electricity produced in France.
