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Created by Andy Darvill,
Science teacher at
Broadoak Community School,
Weston-super-Mare, England
Web site www.darvill.clara.net
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We have
used running water as an energy source for thousands of years,
mainly to grind corn.
The first
house in the world to be lit by hydroelectricity was Cragside
House, in Northumberland, England, in 1878. In 1882 on the
Fox river, in the USA, hydroelectricity produced enough power
to light two paper mills and a house.
Nowadays
there are many hydro-electric power stations, providing around
20% of the world's electricity. The name comes from "hydro",
the Greek word for water.
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How
it works
A dam is
built to trap water, usually in a valley where there is an existing
lake.
Water is
allowed to flow through tunnels in the dam, to turn turbines
and thus drive generators.
Notice that
the dam is much thicker at the bottom than at the top, because
the pressure of the water increases with depth.
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Hydro-electric
power stations can produce a great deal of power very cheaply.
When it
was first built, the huge "Hoover Dam", on the Colorado
river, supplied much of the electricity for the city of Las
Vegas; however now Las Vegas has grown so much, the city gets
most of its energy from other sources.
There's
a good explanation of how hydro power works at www.fwee.org.
Although
there are many suitable sites around the world, hydro-electric
dams are very expensive to build. However,
once the station is built, the water comes free of charge, and
there is no waste or pollution.
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The Sun
evaporates water from the sea and lakes, which forms clouds
and falls as rain in the mountains, keeping the dam supplied
with water.
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More
details
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Gravitational
potential energy is stored in the water above the dam. Because
of the great height of the water, it will arrive at the turbines
at high pressure, which means that we can extract a great deal
of energy from it. The water then flows away downriver as normal.
In mountainous
countries such as Switzerland and New Zealand, hydro-electric
power provides more than half of the country's energy needs.
An alternative
is to build the station next to a fast-flowing river. However
with this arrangement the flow of the water cannot be controlled,
and water cannot be stored for later use.
See
also: www.fuelfromthewater.com
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- Once
the dam is built, the energy is virtually free.
- No waste
or pollution produced.
- Much
more reliable than wind, solar or wave power.
- Water
can be stored above the dam ready to cope with peaks in demand.
- Hydro-electric
power stations can increase to full power very quickly, unlike
other power stations.
- Electricity
can be generated constantly.
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Disadvantages
- The dams
are very expensive to build.
However, many dams are also used for flood control or irrigation,
so building costs can be shared.
- Building
a large dam will flood a very large area upstream, causing problems
for animals that used to live there.
- Finding
a suitable site can be difficult - the impact on residents and
the environment may be unacceptable.
- Water quality
and quantity downstream can be affected, which can have an impact
on plant life.
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Is
it renewable?
Hydro-electric
power is renewable.
The Sun provides the water by evaporation from the sea, and will keep
on doing so.
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