Environmental Engineering Reference
In-Depth Information
generator convert the energy of the water into electric energy. The energy output is
not continuous, so that when the tide goes out output drops to zero.
Tides were used by tidal mills even during the Middle Ages. Worldwide there are
only very few modern tidal power plants in operation today. The biggest and best-
known one is the Rance power plant in France, which is situated on the estuary of
the river of the same name and came into operation in 1967. It has a power output
of 240 megawatts. The dam wall that seals off the 22 km
2
basin is 750 m long. The
environmental impacts of the separation of the estuary from the ocean are consider-
able. Corrosion by salty sea water is also causing some problems.
Tidal power plants are comparatively expensive to operate, so it is not likely that
many new plants will be built. Due to the relatively minor differences between ebb
and fl ow, most countries do not have suitable locations for these plants.
9.3.5 Wave Power Plants
For decades high hopes have been pinned on the development of wave power plants.
A study of the potential of wave energy indicates that large amounts of energy could
be generated. However, only coastal regions with low water depths are appropriate
for the use of wave energy. Due to the comparatively small useable sea areas avail-
able in many countries, this technology has relatively low potential.
Basically, a distinction is made between the following functions:
■
Float ball systems
■
Chamber systems
■
Tapchan systems
Float ball systems use the energy potential of waves. A fl oat ball follows the move-
ment of waves. Part of the installation is anchored to the ground. The movement of
the fl oat ball can be used by a piston or a turbine.
With chamber systems, a chamber locks in air. The waves cause the water level to
fl uctuate in the chamber. The oscillating water level compresses the air. The dis-
placed air escapes through an opening and powers a turbine and a generator. When
the water column falls, the air fl ows back through the turbine into the chamber
(Figure 9.13 ).
'Tapchan' is an abbreviation for 'tapered channel'. In these systems, waves in
coastal areas or on a fl oating object feed into a tapered and rising channel. An upper
basin captures the waves. When the water fl ows back into the ocean, it powers a
turbine.
Although numerous prototypes have been developed for wave power plants in recent
decades, they have not yet caught on in a major way. The main problem is the
extreme fl uctuation in conditions at sea. On one hand, technical systems must be
designed to save on materials and be cost-effective. On the other hand, storms with
giant waves place extreme pressure on system survival. Many prototype installations
have already fallen victim to storms. However, large companies have now become
involved in the development of wave power plants, so it is likely that these problems
will be solved in due course.
