Ocean Energy

Prof. Park

UTI-111

Essex County College

Ocean Energy

• The world's ocean may eventually provide us with energy to power our homes and businesses. Right now, there are very few ocean energy power plants and most are fairly small. But how can we get energy from the ocean?

• There are three basic ways to tap the ocean for its energy. We can use the ocean's waves, we can use the ocean's high and low tides, or we can use temperature differences in the water. Let's take a look at each.

Wave Energy

• Kinetic energy (movement) exists in the moving waves of the ocean. That energy can be used to power a turbine. In this simple example, to the right, the wave rises into a chamber. The rising water forces the air out of the chamber. The moving air spins a turbine which can turn a generator. When the wave goes down, air flows through the turbine and back into the chamber through doors that are normally closed.

• This is only one type of wave-energy system. Others actually use the up and down motion of the wave to power a piston that moves up and down inside a cylinder. That piston can also turn a generator.

• Most wave-energy systems are very small. But, they can be used to power a warning buoy or a small light house.

Wave Energy

Wave Farm

• The World’s First Wave Farm Goes Live in Portugalby Bridgette Meinhold, 10/22/08

• The world’s first commercial wave farm went live at the end of September in Agucadoura, located off the coast of northern Portugal. Designed by Pelamis Wave Power, the farm employs three Wave Energy Converters – snakelike, semi-submerged devices that generate electricity with hydraulic rams driven by waves. This first phase of the new renewable energy farm is rated at 2.25 MW with 3 machines, and the the second phase will add an additional 25 machines to bring the capacity to 21 MW – enough to power 15,000 homes!

Wave Farm

Tidal Energy

• Another form of ocean energy is called tidal energy. When tides comes into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant.

• Tidal energy has been used since about the 11th Century, when small dams were built along ocean estuaries and small streams. the tidal water behind these dams was used to turn water wheels to mill grains.

Tidal Energy

• In order for tidal energy to work well, you need large increases in tides. An increase of at least 16 feet between low tide to high tide is needed. There are only a few places where this tide change occurs around the earth. Some power plants are already operating using this idea. One plant in France makes enough energy from tides (240 megawatts) to power 240,000 homes.

• This facility is called the La Rance Station in France. It began making electricity in 1966. It produces about one fifth of a regular nuclear or coal-fired power plant. It is more than 10 times the power of the next largest tidal station in the world, the 17 megawatt Canadian Annapolis station.

Tidal Energy

La Rance Tidal Power Plant

Tidal Energy

• Tidal energy is the utilization of the sun and moon's gravitational forces - as the tide is the result of their influences.

• Tidal energy is a type of energy that produces electricity and other forms of power through the use of water.

• Tidal energy is energy that could be obtained from the changing sea levels. In other words, tidal energy is a direct result of tide shifting from low to high.

• Tidal energy is one of the oldest forms of energy. Tide mills, in use on the Spanish, French and British coasts, date back to 787 A.D. Tide mills consisted of a storage pond, filled by the incoming tide through a sluice and emptied during the outgoing tide through a water wheel.

Tidal Energy

• The tide moves a huge amount of water twice each day and although the tidal energy supply is reliable and plentiful, converting it into useful electrical power is not easy.

• There are two basic theories on how to convert tides into power. The first involves converting the power of the horizontal movement of the water into electricity. The second involves producing energy from the rise and drop of water levels.

Severn Barrage Tidal Power

• The Severn Barrage is a proposed tidal power station to be built across the Bristol Channel (Severn Estuary). The River Severn has a tidal range of 14 metres - the second highest in the world - making it perfect for tidal power generation.

• The 20 billion pound ($US30bn) Severn Barrage would involve the construction of a 10 mile long barrage (dam) between Lavernock Point south of Cardiff, Wales, and Brean Down in Somerset, England. The barrage would act as a bridge between England and Wales and will have an operational lifetime of up to 200 years. It would be the world's largest ever renewable energy project, and the UK's largest engineering project since the Channel Tunnel.

Severn Barrage Tidal Power

Tidal Energy• Energy calculations• The energy available from a barrage is dependent on the volume of water.

The potential energy contained in a volume of water is:[49]

• where:• h is the vertical tidal range, • A is the horizontal area of the barrage basin, • ρ is the density of water = 1025 kg per cubic meter (seawater varies

between 1021 and 1030 kg per cubic meter) and • g is the acceleration due to the Earth's gravity = 9.81 meters per second

squared. • The factor half is due to the fact, that as the basin flows empty through the

turbines, the hydraulic head over the dam reduces. The maximum head is only available at the moment of low water, assuming the high water level is still present in the basin.

Ocean Thermal Energy Conversion (OTEC)

• The idea is not new. Using the temperature of water to make energy actually dates back to 1881 when a French Engineer by the name of Jacques D'Arsonval first thought of OTEC. The final ocean energy idea uses temperature differences in the ocean. If you ever went swimming in the ocean and dove deep below the surface, you would have noticed that the water gets colder the deeper you go. It's warmer on the surface because sunlight warms the water. But below the surface, the ocean gets very cold. That's why scuba divers wear wet suits when they dive down deep. Their wet suits trapped their body heat to keep them warm.

Ocean Thermal Energy Conversion (OTEC)

• Power plants can be built that use this difference in temperature to make energy. A difference of at least 38 degrees Fahrenheit is needed between the warmer surface water and the colder deep ocean water.

• Using this type of energy source is called Ocean Thermal Energy Conversion or OTEC. It is being demonstrated in Hawaii. More info on OTEC can be found on the archive pages for the Natural Energy Laboratory of Hawaii at: www.hawaii.gov/dbedt/ert/otec-nelha/otec.html

Diagram of a closed cycle OTEC plant