Enhanced geothermal system
The hot dry rock method (in short: HDR) is a process for the utilization of geothermal energy contained in the Earth's body from a depth of 3000-6000 meters. The same principle is described in terms of HFR ( Hot Fractured rock ) and Enhanced Geothermal System (EGS ).
Technology
The principle is based on the production and operation of an oversized heat exchanger in the ground between at least two drill holes. Result of the injection of water with pressure up to 150 bar, the existing cracks in the rock broad despite the rock pressure, and new elements are generated. These remain permanently open, with an average width of less than one millimeter. Thus, a heat exchanger with a huge surface is created in the mountains between the boreholes. During operation, the system is fed cold water through a hole and another hole, possibly enriched by naturally existing deep water, heated accepted again. The natural thermal buoyancy forces of the hot water facilitate the circulation.
Common applications for the art, for example in the Deep Heat Mining Basel and the European Deep Geothermal Power Programs in Soultz -sous -Forêts.
History
The first great HDR project emerged in Europe in Soultz -sous -Forêts (Alsace ). In a four -month trial in 1997 created there the heat exchanger provided at least three square kilometers of hot water with a temperature of 142 ° C. Meanwhile, the holes were deepened to over 5,000 meters to reach a temperature level of 200 ° C. Thus, then a first power plant with a steam temperature of about 180 ° C could operate as a scientific pilot plant to generate electricity.
The Google Foundation sees the HDR method as a technique, which could be used in the future on a large scale as an energy source, and thus promoted the development of the HDR process over 10 million U.S. dollars.
Criticism
Result of the injection of water changes when using the HDR method of the stress state of the rock. It comes to tiny earthquakes that lead to an expansion of existing cracks, so that the surface area increases, at which warms the water pressed. The magnitude of this earthquake is many geothermal experts believe but so small that they are barely noticeable and do not cause damage. Critics of the process, however, fear that the HDR process can also trigger larger earthquakes. So it was in December 2006 when Deep Heat Mining project in Basel not only to the expected smaller quake, but noticeable earthquakes with a magnitude of up to 3.5 points on the Richter scale. Major damage did not occur, but the uncertainty of the population led to the stop of the project. Experts in geothermal expressed in the newspaper Die Welt that these artificially triggered earthquakes could reduce the risk of new Basel earthquake. This effect is, however, considered by the Swiss Seismological Service to be negligible.