ave you ever gone swimming in the ocean? Did H a wave knock you down? The ocean can pack a powerful punch. People have learned how to use that power to generate . One way ofHigh doing so Tideis to use thefor Power natural energy of the . The simplest way to do this is to build a across an inlet. An inlet is a narrow stretch of water that The Rance Plant leads from a large body of water provides enough electricity to power 240,000 homes! toward land. As the rises, c e s workers open gates on the dam,

and water flows into the inlet. Water rushing through The gates close when the area the Rance dam gy R e s o u r gy behind the dam is filled with water. When the tide is low, Renewable Energy Energy Renewable

En er 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. Rance Tidal That’s how the Rance Tidal Power Plant in France works. Power Plant It was the world’s first tidal power station. The plant France produces electricity without adding greenhouse gases to the atmosphere. And its energy source—ocean water—will never run out!

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© Learning A–Z All rights reserved. Credits: left: © FORGET Patrick/SAGAPHOTO.COM/Alamy; www.sciencea-z.com Investigation File right: © Photofusion Picture Library/Alamy 1 Windmills Under the Sea? Farming the Sea Are those underwater windmills? No! They’re tidal turbines. Instead of wind, water makes them turn. Old McDonald had a farm . . . on the seafloor? Tidal turbines work a lot like When many tidal turbines are placed together, it’s called a windmills, but they’re on the tidal farm. Tidal farms can make more electricity than one sea floor, not on land. These turbine alone can. Tidal energy can be harvested almost turbines have blades shaped anywhere there is a tide. The best places for tidal farms have like an airplane’s propeller. a big difference between high and low tides each day. Do You When water strikes the blades, Know? Tidal farms are often placed the turbine spins. This turns Most places on Earth near people so the electricity a generator, which makes have two high tides and doesn’t have to travel far. two low tides every day. electricity. The electricity then moves through power lines to people’s homes. tidal turbine under the sea What Causes Lunar Tides 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 North Pole B A gravity high tide Moon oceans D Wowser! low tide Over 50% of people in the United Between these two high tides are two low tides (C and D). As Earth States live near a coastline. rotates, the locations of the high and low tides change.

© Learning A–Z All rights reserved. Investigation File Credits: top: © PA Photos/Landov; www.sciencea-z.com Energy Resources } Renewable Energy } Tidal Power bottom left: © iStockphoto.com/Stephen Shankland 2