High Tide for Power
H
Energy Resources
Renewable Energy
ave you ever gone swimming in the ocean? Did
a wave knock you down? The ocean can pack a
powerful punch. People have learned how to use that
power to generate electricity.
The Rance Tidal Power Plant
provides enough electricity
to power 240,000 homes!
One way of doing so is to use the
natural energy of the tides. The
simplest way to do this is to build
a dam across an inlet . An inlet is
a narrow stretch of water that
leads from a large body of water
toward land. As the tide rises,
workers open gates on the dam,
and water flows into the inlet.
Water rushing through
the Rance dam
The gates close when the area
behind the dam is filled with water. When the tide is low,
workers open the gates again. Water rushes out of the dam
and toward the large body of water. As water rushes in
or out, it turns big machines called turbines. The turbines
power generators, which make electricity.
That’s how the Rance Tidal Power Plant in France works.
It was the world’s first tidal power station. The plant
produces electricity without adding greenhouse gases
to the atmosphere. And its energy source—ocean
water—will never run out!
Rance Tidal
Power Plant
France
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Investigation File
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right: © Photofusion Picture Library/Alamy
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Windmills Under the Sea?
Are those underwater windmills? No! They’re tidal turbines.
Instead of wind, water makes them turn.
Tidal turbines work a lot like
windmills, but they’re on the
sea floor, not on land. These
turbines have blades shaped
like an airplane’s propeller.
When water strikes the blades,
the turbine spins. This turns
a generator, which makes
electricity. The electricity then
moves through power lines to
people’s homes.
Farming the Sea
Old McDonald had a farm . . . on the seafloor?
When many tidal turbines are placed together, it’s called a
tidal farm. Tidal farms can make more electricity than one
turbine alone can. Tidal energy can be harvested almost
anywhere there is a tide. The best places for tidal farms have
a big difference between high and low tides each day.
Do You
Tidal farms are often placed
Know?
Most places on Earth
near people so the electricity
have two high tides and
doesn’t have to travel far.
two low tides every day.
What Causes Lunar Tides
tidal turbine under the sea
The Moon’s gravity pulls on Earth. Water collects on the Moon-facing
side of Earth (A). Water also collects on the opposite side (B). These
are high tides.
low tide
C
EARTH
high tide
B
North Pole
gravity
high tide
oceans
Moon
D
Wowser!
Over 50% of people in the United
States live near a coastline.
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A
low tide
Between these two high tides are two low tides (C and D). As Earth
rotates, the locations of the high and low tides change.
Investigation File
Energy Resources } Renewable Energy } Tidal Power
Credits: top: © PA Photos/Landov;
bottom left: © iStockphoto.com/Stephen Shankland
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