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.
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
Hydro-electric power stations can produce a great
deal of power very cheaply.
Hydro power - how it works
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
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.
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. For free.
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
Hoover Dam in 1 minute
Once the dam is built, the energy is virtually
No waste or pollution produced.
Much more reliable than wind, solar or wave
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.