Environmental Engineering Reference
In-Depth Information
Small plants use the Ossberger turbine, which is also called a cross-fl ow turbine.
These turbines reach somewhat lower effi ciencies of around 80%. The turbine is
divided into three parts that can be powered separately by water. This helps the
system cope with fl uctuations in the water runoff of small rivers.
9.3 Hydropower Plants
The energy that can be exploited from water essentially depends on two parameters:
runoff volume and the head of the water. Almost all hydropower plants utilize
natural elevation differences using technical equipment.
9.3.1 Run-of-River Power Plants
The natural course of a river itself concentrates large quantities of water. A run-of-
river power plant can be built anywhere on a river where a suffi cient difference in
elevation exists (Figure 9.8). The weir then backs up the water. This creates a dif-
ference in elevation in the water's surface above and below the plant. At the top
the water fl ows through a turbine that powers an electric generator. Grating at the
turbine intake prevents rubbish and fl otsam washed along by the river from blocking
up the turbine. A transformer then converts the voltage of the generator into the
desired mains voltage.
Figure 9.8
Principle of a run-of-river power plant.
Large hydropower plants are usually constructed so that multiple turbines can run
in parallel. If the water fl ow drops during the dry periods of the year, some of the
turbines can be shut down. The remaining turbines then still receive almost the full
amount of water they need. This prevents the turbines from working in partial-load
mode with poor effi ciency. If, on the other hand, there is fl ooding and a river carries
more water with it than the turbines can process, the surplus water has to be let out
unused over a weir.
