We've used the wind as an energy source for a long time. The
Babylonians and Chinese were using wind power to pump water for
irrigating crops 4,000 years ago, and sailing boats were around long
before that.
Wind power was used in the Middle Ages, in Europe, to grind corn,
which is where the term "windmill" comes from.
How it works
The Sun heats our atmosphere unevenly, so some patches become warmer
than others.
These warm patches of air rise, other air blows in to replace them -
and we feel a wind blowing.
We can use the energy in the wind by building a tall tower, with a
large propellor on the top.
The wind blows the propellor round, which turns a generator to
produce electricity.
We tend to build many of these towers together, to make a "wind
farm" and produce more electricity.
The more towers, the more wind, and the larger the propellors, the
more electricity we can make.
It's only worth building wind farms in places that have strong,
steady winds, although boats and caravans increasingly have small
wind generators to help keep their batteries charged.
More details
The best places for wind farms are in coastal areas, at the tops of
rounded hills, open plains and gaps in mountains - places where the
wind is strong and reliable.
To be worthwhile, you need an average wind speed of around 25 km/h.
Most wind farms in the UK are in Cornwall or Wales.Isolated places such as farms may have their own wind generators.
In California, several "wind farms" supply electricity to homes
around Los Angeles.
The propellors are large, to extract energy from the largest
possible volume of air. The blades can be angled to "fine" or
"coarse" pitch, to cope with varying wind speeds, and the generator
and propellor can turn to face the wind wherever it comes from.
Some designs use vertical turbines, which don't need to be turned to
face the wind.
The towers are tall, to get the propellors as high as possible, up
to where the wind is stronger. This means that the land beneath can
still be used for farming.
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