| Tidal power traditionally involves erecting a dam | | | | tide to high tide is needed. There are only a few |
| across the opening to a tidal basin. The dam includes | | | | places where this tide change occurs around the |
| a sluice that is opened to allow the tide to flow into | | | | earth. Some power plants are already operating using |
| the basin; the sluice is then closed, and as the sea | | | | this idea. One plant in France makes enough energy |
| level drops, traditional hydropower technologies can | | | | from tides to power 240,000 homes. |
| be used to generate electricity from the elevated | | | | 3. Ocean Thermal Energy |
| water in the basin. Some researchers are also trying | | | | The final ocean energy idea uses temperature |
| to extract energy directly from tidal flow streams. | | | | differences in the ocean. If you ever went swimming |
| There are three basic ways to tap the ocean for its | | | | in the ocean and dove deep below the surface, you |
| energy. We can use the ocean's waves, we can use | | | | would have noticed that the water gets colder the |
| the ocean's high and low tides, or we can use | | | | deeper you go. It's warmer on the surface because |
| temperature differences in the water. | | | | sunlight warms the water. But below the surface, the |
| 1. Wave Energy | | | | ocean gets very cold. That's why scuba divers wear |
| Kinetic energy (movement) exists in the moving | | | | wet suits when they dive down deep. Their wet |
| waves of the ocean. That energy can be used to | | | | suits trapped their body heat to keep them warm. |
| power a turbine. In this simple example, the wave | | | | Power plants can be built that use this difference in |
| rises into a chamber. The rising water forces the air | | | | temperature to make energy. A difference of at |
| out of the chamber. The moving air spins a turbine | | | | least 38 degrees Fahrenheit is needed between the |
| which can turn a generator. When the wave goes | | | | warmer surface water and the colder deep ocean |
| down, air flows through the turbine and back into the | | | | water. Using this type of energy source is called |
| chamber through doors that are normally closed. | | | | Ocean Thermal Energy Conversion or OTEC. It is |
| This is only one type of wave energy system. | | | | being used in both Japan and in Hawaii in some |
| Others actually use the up and down motion of the | | | | demonstration projects. |
| wave to power a piston that moves up and down | | | | Some of the oldest ocean energy technologies use |
| inside a cylinder. That piston can also turn a | | | | tidal power. All coastal areas consistently experience |
| generator. Most wave-energy systems are very | | | | two high and two low tides over a period of slightly |
| small. But, they can be used to power a warning | | | | greater than 24 hours. For those tidal differences to |
| buoy or a small light house. | | | | be harnessed into electricity, the difference between |
| For more information see: Ocean Energy Potential | | | | high and low tides must be at least five meters, or |
| 2. Tidal Energy | | | | more than 16 feet. There are only about 40 sites on |
| Another form of ocean energy is called tidal energy. | | | | the Earth with tidal ranges of this magnitude. If there |
| When tides comes into the shore, they can be | | | | is one thing we can safely predict and be sure of on |
| trapped in reservoirs behind dams. Then when the | | | | this planet, it is the coming and going of the tide. This |
| tide drops, the water behind the dam can be let out | | | | gives this form of renewable energy a distinct |
| just like in a regular hydroelectric power plant. In | | | | advantage over other sources that are not as |
| order for this to work well, you need large increases | | | | predictable and reliable, such as wind or solar. |
| in tides. An increase of at least 16 feet between low | | | | |