Wave/Tidal Energy

by: Karina Ayala, Rachael Carleson Williams, Lidya Makonnen, Terrell

Stevenson

Wave Energy

WHAT IS IT?• Wave power devices extract

energy directly from surface waves or from pressure fluctuations below the surface. 

• Energy extracted from the waves is stored in generators.

• Wave energy can be converted into electricity through both offshore and onshore systems.

• Offshore systems are situated in deep water, typically of more than 40 meters (131 feet). Sophisticated mechanisms—like the Salter Duck—use the bobbing motion of the waves to power a pump that creates electricity. Other offshore devices use hoses connected to floats that ride the waves. The rise and fall of the float stretches and relaxes the hose, which pressurizes the water, which, in turn, rotates a turbine.

Oscillating water column The oscillating water column consists of a partially submerged concrete or steel structure that has an opening to the sea below the waterline. It encloses a column of air above a column of water. As waves enter the air column, they cause the water column to rise and fall. This alternately compresses and depressurizes the air column. As the wave retreats, the air is drawn back through the turbine as a result of the reduced air pressure on the ocean side of the turbine.

HOW DOES IT WORK?1. Wave capture chamber set into rock face.– Tidal power forces water into chamber.– Air alternately compressed and

decompressed and decompressed by "oscillating water column".

– Rushes of air drive the Wells Turbine, creating power.

TAPCHANTapered channel system, consists of a tapered channel, which feeds into a reservoir constructed on cliffs above sea level. The narrowing of the channel causes the waves to increase in height as they move toward the cliff face. The waves spill over the walls of the channel into the reservoir and the stored water is then fed through a turbine.

• The TAPCHAN systems overcome the issue of power on demand, as the reservoir is able to store energy until it is required.

Pendulor device The pendulor wave-power device consists of a rectangular box, which is open to the sea at one end.

A flap is hinged over the opening and the action of the waves causes the flap to swing back and forth. The motion powers a hydraulic pump and a generator.

Main Advantages

• This is a non-polluting source of energy• Wave turbines are relatively quiet to operate and do not affect

wild life.

Main Disadvantages• Wave energy requires a consistent supply of powerful waves

to fuel a community's electrical needs, but waves are not consistent.

•  Spills or accidental leaks caused by hydraulic fluids in the system could also potentially harm marine life.  

Tidal Energy

WHAT IS IT?• Tides of water caused by the

Moon and Sun, in combination with Earth's rotation.

• Practically inexhaustible and it is classified as a renweable resource.

• For tidal differences to be harnessed into electricity the difference between high and low tides must be at least 16 feet.

• There are only about fourty sites on the earth with tidal ranges of this magnitude.

Tidal power technologies include the following...

Barrage or damA barrage or dam is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator.

Gates and turbines are installed along the dam. When the tides produce an adequate difference in the level of the water on opposite sides of the dam, the gates are opened. The water then flows through the turbines. The turbines turn an electric generator to produce electricity.

Tidal fence Tidal fences look like giant turnstiles. They can reach across channels between small islands or across straits between the mainland and an island.

A tidal fence has vertical axis turbines mounted in a fence. All the water that passes is forced through the turbines. They can be used in areas such as channels between two landmasses.

Tidal turbine Tidal turbines look like wind turbines. They are arranged underwater in rows, as in some wind farms.

•  Ideal locations for tidal turbine farms are close to shore in water depths of 65.5–98.5 feet.

 • Turbines were submerged in the East River to generate

electricity from rapid tidal currents in New York City in 2007

Main Advantages

• It is predictable. •  No waste or pollution•  It is very cheap to maintain.

Main Disadvantages

• Building cost is expensive.•  Disrupts migration of creatures

in the ocean•  Only produces power for only

about 10 hours a day.

THE END...

SOURCES • http://www.energysavers.gov/

 • http://www.rise.org

 • http://www.technologyreview.com/energy/

 • http://en.wikipedia.org/wiki/Tidal_power

 • http://en.wikipedia.org/wiki/Wave_power