Environmental Engineering Reference
In-Depth Information
around 3.6 megawatts is the fi rst one to use the Kalina process. In addition,
the plant feeds heat with a thermal capacity of 28 megawatts into a district
heating grid.
Other countries such as the USA have been using geothermal power for more than
50 years and have much larger capacities. The Geysers, 116 km north of San
Francisco, is the largest dry steam fi eld in the world. The construction on The
Geysers began in 1960. Today 15 power plants there have a net electricity-
generating capacity of about 725 megawatts, enough to power a city the size of San
Francisco.
■
iga.igg.cnr.it
International Geothermal Association
■
geothermal.marin.org
Geothermal Education Offi ce
10.2.3 Geothermal HDR Power Plants
At drill depths of up to 5000 m temperatures are around 200 °C, even in regions that
do not benefi t from optimal geothermal conditions, such as Germany, France and
Switzerland. As a result, fully acceptable effi ciency is achieved in power generation
provided the depth is great enough.
Thermal water cannot usually be exploited at such great depths. What is mainly
found is HDR (hot dry rocks). Artifi cial shafts are created in which water can be
heated to extract the heat from the rocks. These shafts are made by compressing
water at high pressure into a borehole. The heat expands the borehole, creates new
fi ssures and expands existing cracks. This produces an underground fracture system
that can extend to several cubic kilometres. A listening borehole monitors the
activities.
This direct tapping of hot water deposits is also referred to as hydrothermal
geothermal energy, whereas hot-dry-rock technology is also called petrothermal
geothermal energy.
To generate geothermal energy, a pump transports cold water through an injection
well into the depth. There the water disperses into the cracks and fi ssures of the
crystalline rock and heats up to temperatures of 200 °C. The hot water reaches the
surface again through production wells and delivers the heat over a heat exchanger
to a power plant process and district heating grid (Figure 10.9).
During the 1970s the Los Alamos laboratory in the USA conducted the fi rst tests
of the HDR method. A European research project on HDR technology has been
underway in Soultz-sous-Fôrets in Alsace since 1987. Its goal is to implement a
pilot power plant. In 2004 Geopower Basel AG was founded in Switzerland with
the aim of building the fi rst commercial HDR power plant, but work on the project
was stopped in 2007 when small tremors occurred during the creation of the under-
ground fractures.
