Environmental Engineering Reference
In-Depth Information
Storage power plants can be constructed with a second basin located at a lower
elevation at the machine house. Special pump turbines can then pump the water
from the lower basin back up to the higher basin. This is called a pumped-storage
power plant.
9.3.3 Pumped-Storage Power Plants
Pumped-storage power plants need very specifi c geographical conditions. To be
built, they need two basins with a major difference in altitude between them. Some
pumped-storage plants have a natural infl ow where a river fl ows into the higher
basin. Pumped-storage plants without a natural infl ow are purely storage plants.
When electric power is needed, the water of the higher basin is pumped over an
intake mechanism through a pressure pipe to the turbine, which drives an electric
machine as the generator. Once the turbine has extracted the energy from the water,
the water fl ows into the lower basin. A transformer there converts the voltage of
the generator to mains voltage (Figure 9.11).
Figure 9.11
Principle of a pumped-storage power plant.
When electricity surpluses occur in the grid, the pumped-storage plant switches over
to pumping operation. The electric machine then functions as a motor that drives
the pump turbine. The pump turbine pumps the water from the lower to the higher
basin once again. Major fl uctuations in pressure can occur when the generator is
switched to pumping operation, and, in an extreme case, these fl uctuations can cause
damage to the pressure pipe or other system parts. A surge tank regulates this change
in pressure.
Pumped-storage power plants reach effi ciencies of 70 to 90%. A good 70% of
the electric energy that is necessary for pumping the water to the higher level can
be replaced during the operation of the generator. Despite the losses, pumped-
storage plants are very attractive economically. When a surplus of supply exists,
electricity can usually be obtained very inexpensively. On the other hand, if
electricity is in low supply, a plant can feed the energy back into the grid at a higher
price.
