Wave energy originates with the energy of the wind, which originates from the Sun's energy.
When
the wind hits the water, it pushes the water, lifting it (gravitational
potential energy) - it then falls back down under gravity and becomes
kinetic energy of the water.
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Oscillating Water Column (OWC)
One of the ways to
capture some of this energy is the oscillating water column.
When waves hit an OWC, the air inside is compressed and forced through
air turbines - these turn the generator and make electricity by electromagnetic
induction.
- The wave capture
chamber is set in a rigid structure like a cliff face - or in a
tower built on the sea-bed..
- Wave power
forces water into the chamber
- Air is alternately
compressed and decompressed in the OWC
- Compressed
air forces the turbine to turn
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Salter Ducks
"Salter
Ducks" are floating canisters that are connected in a chain of
about 25 across the sea. Each float is called a 'Duck' because it bobs
up and down! It about the size of a double decker bus! It weighs about
300-tonnes and is designed to drive a generator from the motion of bobbing
up and down on waves like a duck. It. This system has the potential to
capture a lot of energy,
The untimely death
of Salter's Duck
The Duck was developed
in the late '70s by a team headed by Professor Stephen Salter at Edinburgh
University. This was one of several research groups set up after a 1976
judgment by the Department of Energy that wave power was the most promising
renewable energy source.
By 1982, a consultant
was able to report that the duck could be expected, with further development,
to produce electricity at a cost of around 5.5 pence (about 12 cents)
per kilowatt-hour, a price competitive with nuclear power (the most expensive
commercial generation process in use in Britain). Clive Grove-Palmer,
a respected department engineer seconded to work on the duck project,
estimated that the cost could be got down around 3 pence per kilowatt-hour
(about 7 cents).
But there was opposition
from established energies (especially the atomic energy branch) in the
UK and in 1983 data relating to the project was incorrectly put forward
making those responsible for the funding to withdraw their support. Some
people suspected it had been done deliberately - the researchers did not
see the final paper until 8 months after it had sunk the Duck! After a
long campaign to save the project, Professor Salter's team was forced
to disperse in early 1987. Since the cost inflation (it said that it would
cost 10X as much!) of the report has come to light there has been some
talk of resurrecting the Duck - but the original researchers have now
moved on to other work or retired. However, it does look as if the Duck
may rise again!
History
Getting energy from
the waves has been studied since the time of the French Revolution when
the first patent was filed in Paris by a father and son named Girard.
They noted that the enormous mass of a ship of the line, which no
other known force is capable of lifting, responds to the slightest wave
motions.
There was little progress
in turning wave motions into useful energy until the last quarter of the
20th century, mainly through lack of scientific knowledge of what a wave
was, how it travelled and how it could be converted into useful energy.
What is a wave?
Leonardo da Vinci
noted that when the wind blew across a field of corn, it looked as though
waves of corn ran across the field whereas, in fact, the individual
heads were only moving slightly. So it is with waves in the sea!
The particles
themselves do not progress along to the shore - the wave energy does!
See Waves.
So, unlike hydro-electric
power it cannot use a flow of water running in one direction. You cannot
put a water wheel in the sea and leave it to revolve and generate electricity,
even though, to the watcher on the shore, it appears that the waves are
advancing towards the beach in a straight line!
A water particle in
a wave travels up and down. Its height is the key indication of its power
as this is linked to its potential gravitational energy. So the rougher
the sea, the more potentially fruitful it is but also the harder
it is to harvest! Wave energy engineers have to design a power station
that can absorb the power of the most ferocious waves without being wrecked.
Advantages of wave
power
Wave energy has been
hailed as the most promising renewable source for maritime countries.
It does no environmental damage and is inexhaustible the waves
go on for ever.
Design Issues and
Problems
Wave power devices
have to be carefully planned out. Many are designed to float in the ocean,
and can be damaged by powerful waves and storms. Other designs, like the
OWC, are attached to a rigid face and are more able to withstand nature's
everyday force. Also, to get the most energy from the waves, OWC's are
best designed with two-way turbines, so that air can be pushed out or
sucked in, always creating energy.
Useful Link:
http://www.esru.strath.ac.uk/EandE/Web_sites/98-9/offshore/wave.htm
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