Thermomineral Water and Geothermal Energy - Hydrogeology: Objectives, Methods, Applications - page 86

the edge of the Rhine Graben. Since 2005 a triplet of deep boreholes enables
the injection and the circulation of water into fractured granite. The main
problems were induced earthquakes, corrosion and diffi culties to clean
the granite fractures to enable the water circulation between the boreholes.
The water is laterally collected by two pumps (12 and 3 L.s -1 ) and led to a
thermal exchanger, which powers an electric turbine with steam (Figure 48).
The fi rst electricity has been produced in 2008 and is now delivered in the
French electricity network. A larger plant, with three injection wells and six
collection wells, will be built in order to increase production to 25 MWe.
Figure 48 Conceptual mechanism at Soultz-sous-Forêts (Bas Rhin) (from Baumgärtner,
2002).
High energy sites are used in Iceland and in the USA, in Northern
California, which is home to the largest geothermal power plant in the
world: the Geysers (2000 MWe), one of the sources of energy for San
Francisco. Its capacity is, however, currently limited to 1,200 MWe due to
a decrease in the vapor fl ux.