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Further information on wave energy |
TAPCHAN
is
the name of a prototype generator that was installed
on a remote Norwegian island in 1985 and has been functioning
ever since. The name is an abbreviation of ‘tapered
channel’, which describes the basic idea behind the
device. TAPCHAN consists of a reservoir built into a
cliff a few metres above sea level. Leading into it
is a tapered channel – wide at the mouth, which is open
to the sea, and becoming narrower as it penetrates the
reservoir. Incoming waves increase in height as they
move up the channel, eventually overflowing the lip
of the channel and pouring into the reservoir. In this
way, TAPCHAN converts the kinetic energy of the wave
into potential energy, which is subsequently converted
into electrical energy by a generator as the water is
fed back to the sea through a pipe.
OWC
Another kind of wave energy converter is known as
the oscillating water column (OWC). Like TAPCHAN, this
is a fixed device – which means that the housing of
the device does not move - located either onshore or
fixed to the seabed. It consists of a wedge-shaped chamber
that is open to the sea at the bottom. A wave surging
into this chamber forces air upwards, which drives a
turbine both on its way up (as the wave surges) and
on its way down (as the wave recedes). These oscillations
give the device its generic name. To take best advantage
of this two-way flow, a special kind of turbine (such
as the British-designed Wells turbine) is needed.
The ‘duck’ is an example of a floating wave energy converter. It is not fixed to the shore or seabed, relying instead on the ‘nodding’ motion of floats to drive a generator. In fixed devices, the turbine is fixed while the water or air rushes past its blades. Floating devices generate their power by the relative motion of components as they bob up and down in the sea. The duck consists of rows of floats, each generating electricity that is fed ashore by a connecting cable.
One of the advantages of floating devices over fixed devices it that they can be deployed in deeper water, where wave energy is greater (since waves lose energy with decreasing water depth). There is no need for significant earthworks, either, as there is with onshore devices.
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