The geothermal energy potential of the planet remains largely under-exploited, in particular in many developing countries - the example of the Philippines is by no means typical! But in these countries, as is often the case for other renewable energies, the brake on the development of geothermal energy is the lack of investment capital.
A geothermal well is expensive. Furthermore, preliminary studies, construction and operation require competent and well-trained personnel. Developing countries remain largely dependent on external aid …
In developed countries, geothermal energy will continue to develop, but slowly. In Europe, installed power (theoretical production capacity) of 990 MWe is planned by 2010 (+ 20% compared to 2004). For the production of geothermal heat, planned progression is more rapid: 17 500 MWth by 2010 (+ 235% compared to 2004).
On the technical side, interest is not focused uniquely on
the flow of
hot underground water.
For several years, tests have been conducted on the injection of water into “dry” rocks (for example, a fractured or distorted granite massif), situated at a great depth and on a thermal anomaly (steep geothermal gradient), where one finds very high temperatures. The principle is to drill two wells at a certain distance from one another (several hundred meters). Into one, water is injected under high pressure, enlarging, or even creating, a network of fractures in the rock. Water, reheated by its passage through the high temperature rocks, is pumped into the second well. Once the network of fractures in the rocks is of good quality for water circulation, everything is in place for the injection of a constant flow of cold water into the rocks and recovery of hot water.
A test of this type has been conducted in the Alsace, at Soultz-sous-Forêts, since 2002. The wells are drilled to a depth of 5000 m in the heart of a granite massif. The water passes through rocks whose temperature exceeds 200°C. If the test proves a success, a small geothermal energy plant of 6 thousand kilowatts could begin electricity production from 2006.
A trial of this type has been going on since 2002, in Alsace, at Soultz-sous-Forêt. The wells have been sunk to 5 000 m in the heart of a granite mountain mass. The water passes through rocks whose temperature exceeds 200° C. A small turbine of 1.5 MWe should be working from the beginning of 2008. The next stage will be the construction of a plant of some 20 MW. The project is advancing with prudence, since a similar trial in Switzerland (going on since 1996, near Bâle), where the pressure of the injected water was very high, caused an earth tremor of magnitude 3.4 on the Richter scale in 2007. Whilst damage was slight (mainly cracks in walls), the project was immediately suspended for at least 2 years. It must be said that the city had been entirely destroyed in 1356 by an earthquake, due to natural causes in that instance. Bad memories… The technique cannot avoid provoking micro-tremors. But they are without importance, if they can be limited to a magnitude of less than 2 on the Richter scale. |