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Getting
Electricity from the Wind
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The potential for using the
wind to generate electricity is huge. A recent study for
the European Community estimated that there were sufficient
sites in Europe for about 400,000 big machines, enough
to provide three times Europe’s present needs.
Modern wind generators are very different from the old
windmills. They are more like giant propellers with two
or there blades, called rotors, mounted on top of tall
towers of steel or concrete. The rotors turn a shaft which
drivers an electric generator.
The size of the blades the height of the tower determine
how much electricity the machine can generate. Wind generally
gets stronger as you go higher, and the power of the wind
you capture depends on the swept area of the blades. Double
the length of the blades and the power increases four-fold.
More important still is the speed of the wind, for the
power that can be extracted goes up as the cube of wind
speed, if it blows twice as hard, there is eight times
as much power to be had. |
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However, wind generators do not
need, or want, stormy weather, most machines are designed to
operate at wind speeds between Force 3 and Force 10 on the Beaufort
Scale-13 to 60mph (21 to 97km/h). Above Force 10 the machines
automatically shut down to save themselves from flying apart.
Most machines are designed to produce much the same power throughout
their working range, the blades automatically ‘feathering’
as the wind increases to that the machine does not accelerate
too much. It is better to have a steady output over a wide range
of wind speeds that to be able to take advantage of the few
really strong gusts.
Wind generators must point in the right direction, either directly
towards the wind or directly away from it. For this reason rotor
is mounted on a turntable and controlled by an electric motor
connected to sensors, which tell it which way to face.
This problem of wind direction can be avoided completely if
the blades are mounted on a vertical rather than horizontal
axis. Then it does not matter where the wind is blowing from.
These vertical machines, called Darreius Turbines, have other
advantages. The heavy generating machinery that converts to
power into electricity can be placed on the ground, rather than
at the top of a tower. The rotor is, therefore, subjected to
less stress than in the horizontal-axis generators. A disadvantage
is that they often need a push to get started, either by hand
or by a electric motor.
One of the main problems of using wind turbines is environmental.
While people like the idea of wind power, they are less keen
on having every hill crowned with a whirling turbine. |
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Serious examination has been
given to placing the turbines out at sea. But there would
be problems anchoring them and in transmitting the power
back to land. The British Department of Energy has estimated
that clusters of wind turbines built in produce one and
a half times Britain’s present electricity demand,
but engineers first want to study the performance of land-based
machines.
The people of Fair Isle, off the north coast of Scotland,
have already been making use of wind power. They installed
a small wind generator in the early 1980s and have cut
electricity bills by more than three-quarters from the
old diesel engines. |
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