http://science.gallery.youngester.com/2009/06/renewable-energy-from-ocean.html
Power is currently being harvested from the ocean in two different ways:
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.
Tidal Energy
Pictures of La Rance Tidal Station 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.
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.
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.
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.
Advantages of Tidal and Wave Generators
Today’s most promising water-based generators operate something like floating wind turbines anchored to the sea floor. Moving ocean water creates pressure that turns a hydraulic turbine, which in turn is linked to a generator that converts the hydraulic energy into electricity.
Ocean-powered generators have important advantages over both conventional forms of power and other renewable energy alternatives, such as wind and solar power. Ocean-generated energy is:
* Clean. Unlike coal, oil, or nuclear energy, the electricity produced by tidal or wave generators is emission free. Powering houses with ocean-generated electricity could potentially save millions of tons of carbon emissions each year.
* Unobtrusive. Ocean-borne generators ride the waves without protruding above the water’s surface, so they don’t obstruct views the way today’s huge wind turbines can.
* Consistent. Waves and tidal movements are predictable and occur all year round, so ocean generators aren’t affected by clouds or seasonal changes as solar collectors are.
Moving from Experimental Technology to Commercial Reality
Wave and tidal generators are currently in advanced phases of testing or initial commercial operation in several locations around the world. A tidal current generator developed by Sea Generation Ltd. began operating in Northern Ireland’s Strangford Lough in June, 2007, with a potential capacity of 1.2 megawatts. A wave farm consisting of three generators built by Pelamis Wave Power opened off Portugal in September, 2008. Operating at full capacity, the farm can generate enough electricity to power more than 1,500 houses. Both of those projects, though, have been dogged by technical problems caused by the harsh ocean environment.
British company Checkmate Seaenergy developed a new, simpler generator, the Anaconda Wave Energy Converter, to help combat breakdowns caused by the corrosive effects of seawater. While the Seagen and Pelamis turbines are primarily made of metal, the Anaconda is made mainly from fabric and rubber.
A small-scale Anaconda generator has just completed testing in a tank in Hampshire, England. If the tests prove successful, larger versions of the power generator will be tested in the ocean. Checkmate Seaenergy, the Anaconda’s maker, hopes to have wave generators in commercial production by 2014.
Future Prospects for Renewable Energy from the Ocean
Many governments have set ambitious targets for generating electricity from renewable sources. The European Union plans to generate 20% of its electricity from renewables by the year 2020. The United States recently set a target of generating 25% of all electricity renewably by 2025.
As with many new technologies, getting the funding to overcome technical problems and test new installations is one of the major obstacles standing between ocean-power generation and commercial success. Even in a difficult economic climate, the new water-powered generators are promising enough that governments and private companies are pressing ahead with plans to generate a small but significant part of their electricity needs from the ocean.
Generating technologies for deriving electrical power from the ocean include tidal power, wave power, ocean thermal energy conversion, ocean currents, ocean winds and salinity gradients. Of these, the three most well-developed technologies are tidal power, wave power and ocean thermal energy conversion. Tidal power requires large tidal differences which, in the U.S., occur only in Maine and Alaska. Ocean thermal energy conversion is limited to tropical regions, such as Hawaii, and to a portion of the Atlantic coast. Wave energy has a more general application, with potential along the California coast. The western coastline has the highest wave potential in the U.S.; in California, the greatest potential is along the northern coast.
Energy
California has more than 1,200 kilometers (745 miles) of coastline, and the combined average annual deep water wave power flux is over 37,000 megawatts (MW) of which an upper limit of about 20 percent could be converted into electricity. This is sufficient for about 23 percent of California's current electricity consumption. However, economics, environmental impacts, land-use and grid interconnection constraints will likely impose further limits to how much of the resource can be extracted. Although technology is still at a relatively immature pilot project stage, economic projections indicate that ocean energy could become cost-competitive over the long-term.
Current Pilot Projects
In the spring of 2009, the Sonoma County Water District applied to the Federal Energy Regulatory Commission (FERC) for three wave project preliminary permits. The projects will be located in state waters offshore Del Mar Landing (the northwestern portion of the county) and off Fort Ross further to the south. Each of the three projects would begin as pilots in the two to five megawatt (MW) range, could potentially expand to commercial facilities in the 40-200 MW range, and would include substations, transmission lines, appurtenant facilities, and submersible electric cables.
With these applications, the total number of FERC permits and applications for wave and tidal projects in California waters totals twelve.
Wave Energy
Wave energy conversion takes advantage of the ocean waves caused primarily by interaction of winds with the ocean surface. Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid.
Although many wave energy devices have been invented, only a small proportion have been tested and evaluated. Furthermore, only a few have been tested at sea, in ocean waves, rather than in artificial wave tanks.
As of the mid-1990s, there were more than 12 generic types of wave energy systems. Some systems extract energy from surface waves. Others extract energy from pressure fluctuations below the water surface or from the full wave. Some systems are fixed in position and let waves pass by them, while others follow the waves and move with them. Some systems concentrate and focus waves, which increases their height and their potential for conversion to electrical energy.
A wave energy converter may be placed in the ocean in various possible situations and locations. It may be floating or submerged completely in the sea offshore or it may be located on the shore or on the sea bed in relatively shallow water. A converter on the sea bed may be completely submerged, it may extend above the sea surface, or it may be a converter system placed on an offshore platform. Apart from wave-powered navigation buoys, however, most of the prototypes have been placed at or near the shore
The visual impact of a wave energy conversion facility depends on the type of device as well as its distance from shore. In general, a floating buoy system or an offshore platform placed many kilometers from land is not likely to have much visual impact (nor will a submerged system). Onshore facilities and offshore platforms in shallow water could, however, change the visual landscape from one of natural scenery to industrial
The incidence of wave power at deep ocean sites is three to eight times the wave power at adjacent coastal sites. The cost, however, of electricity transmission from deep ocean sites is prohibitively high. Wave power densities in California's coastal waters are sufficient to produce between seven and 17 megawatts (MW) per mile of coastline
According to the European Union, "Among the different converters capable of exploiting wave power, the most advanced is unquestionably the Pelamis Wave Energy Converter, a kind of "undulating sea serpent" developed by Ocean Power Delivery. This technology is the object of a commercial contract for installation of a farm in Portugal. In 2007, three machines, with a total capacity of 2.25 megawatts (MW(, are in installation phase, and should be joined by 27 others in the years to come. Another 5 MW project is being studied for England this time."
None of these plants are located in California, although economic feasibility studies have been performed for a 30 MW wave converter to be located at Half Moon Bay. Additional smaller projects have been discussed at Fort Bragg, San Francisco and Avila Beach. There are currently no firm plans to deploy any of these projects
As of the mid-1990s, wave energy conversion was not commercially available in the United States. The technology was in the early stages of development and was not expected to be available within the near future due to limited research and lack of federal funding. Research and development efforts are being sponsored by government agencies in Europe and Scandinavia
Many research and development goals remain to be accomplished, including cost reduction, efficiency and reliability improvements, identification of suitable sites in California, interconnection with the utility grid, better understanding of the impacts of the technology on marine life and the shoreline. Also essential is a demonstration of the ability of the equipment to survive the salinity and pressure environments of the ocean as well as weather effects over the life of the facility
Permitting Issues. Some of the issues that may be associated with permitting an ocean wave energy conversion facility include:
* Disturbance or destruction of marine life (including changes in the distribution and types of marine life near the shore)
* Possible threat to navigation from collisions due to the low profile of the wave energy devices above the water, making them undetectable either by direct sighting or by radar. Also possible is the interference of mooring and anchorage lines with commercial and sport-fishing.
* Degradation of scenic ocean front views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines
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.
In order for tidal energy to work well, you need relateivel large increases in tides. An increase of at least 16 feet between low tide to high tide is generally needed. There are only a few places where this tide change occurs around the earth. Some power plants are already operating using this idea.
According to the European Union:
"Ninty percent of today's worldwide ocean energy production is represented by a single site: the La Rance Tidal Power Plant (240 MW) that was commissioned in 1966. This type of installation has remained unique in the world and has only been reproduced at much smaller capacities in Canada (20 MW), China (5 MW) and Russia (0.4 MW).
"This type of project was abandoned for many years because of very high initial investment costs as well as the strong local impact that results from it. However, the present economic situation has encouraged South Korea to build a 260 MW dam closing off Sihwa Lake, which is set to be commissioned in 2009. Lighter new techniques, like hydro turbines, are being developed today to harness ocean currents. The leader in this field, the British company, Marine Current Turbine (MCT), should install 1.2MW in Northern Ireland following its 300 kW pilot project in Bristol Bay."
Ocean Thermal Energy Conversion (OTEC)
The idea of 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.
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. The cold ocean water can also be used to cooling buildings, and desalinated water is often a by-product.
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