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The need for searching other types of energy sources substantially increased in the latest decade.
The conventional energy sources as oil, gas, coal start to decrease not to mention the increasing price and pollution "Green energy sources" we can find here on our planet but these sources are not taken into consideration yet due to different reasons like hi cost of technology necessary to "extract" electrical energy from
the Sun, waves, tidal waves, geezers, volcanoes, wind, water currents, etc.


As alternative known sources of energy we can enumerate :

Bio fuel
Biomass
Geothermal
Hydroelectricity
Solar energy
Tidal power
Wave power
Wind power



Our planet is covered by water on approximate 71 % water from oceans. Approximately 71% of the Earth‘s surface (~3.61 X 1014 m2) is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.
Waves_biggest_waves_on_the_planet

More than half of this area is over 3,000 meters (9,800 ft) deep. Average oceanic salinity is around 35 parts per thousand (ppt) (3.5%), and nearly all seawater has a salinity in the range of 30 to 38 ppt.
Scientists estimate that 230,000 marine life forms of all types are currently known, but the total could be up to 10 times that number.
Traditional sources of energy such as oil, gas, and coal are non-renewable. They also create pollution by releasing huge quantities of carbon dioxide and other pollutants into the atmosphere.
In contrast, waves are a renewable source of energy that doesn’t cause pollution. The energy from waves alone could supply the world’s electricity needs. The total power of waves breaking on the world’s coastlines is estimated at 2 to 3 million megawatts. In some locations, the wave energy density can average 65 megawatts per mile of coastline.

 
Corrientes-oceanicas



The solutions to today’s energy challenges need to be explored through alternative, renewable and clean energy sources to enable a diverse national energy resource plan.
An extremely abundant and promising source of energy exists in the world’s oceans. Ocean energy exists in the forms of wave, tidal, marine current, thermal (temperature gradient) and salinity. Among these forms, significant opportunities and benefits have been identified in the area of wave energy extraction.
Waves have several advantages over other forms of renewable energy such as wind and solar, in that the waves are more available (seasonal, but more constant) and more predictable with better demand matching.
Wave energy also offers higher energy densities, enabling devices to extract more power from a smaller volume at consequent lower costs and reduced visual impact.
However, many research and development challenges exist including issues of survivability, maintainability, efficiency, cost reduction, identification of suitable sites, reliable interconnection with the utility grid, better understanding of potential
environmental/marine impacts, and wave resource measurement methodologies for reliable wave energy forecasting and scheduling.

 

aquabuoy_big

Optimizing wave energy technologies requires a multidisciplinary team from areas such as Electrical, Ocean, Chemical, Materials, Civil, Mechanical and Bio Engineering, in addition to the critical Marine Sciences disciplines to enable innovative systems-level research, and successful and responsible development.


Wind, waves and tidal-currents have the potential to generate significant amounts of electrical energy.
The nature and geographical distribution of the resource needs to be well understood for the successful design and implementation of energy converters. The characteristics of the machines that are likely to be to able to make a major contribution to energy production by the year 2020 must be established.
There are numerous potential ways to tap the ocean for energy, from tides, currents, salinity, and even harnessing its thermal features. However, wave energy may be the most promising source of ocean energy for the U.S. coastline, particularly in the Pacific Northwest.


Companies start to utilize more and more the Wave Energy Converters (WEC) are just starting to produce usable electricity.
Waves are generated by wind passing over the surface of the sea. As long as the waves propagate slower than the wind speed just above the waves, there is an energy transfer from the wind to the waves .
Wave power devices extract energy directly from surface waves or from pressure fluctuations below the surface, and are typically located two to three miles (three to five kilometers) offshore.
Waves off the coasts of Oregon, California, Washington, Alaska, and Hawaii have been identified as good sites for the development of wave energy.

Upwelling_wave_or_tidal_


Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example for electricity generation, water desalination, or the pumping of water (into reservoirs).

Wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents. Wave power generation is not currently a widely employed commercial technology although there have been attempts at using it since at least 1890.
The world’s first commercial wave farm was based in Portugal, at the Agucadoura Wave Park, which consists of three 750 kilowatt Pelamis devices.





Generation

The average wind-speed assigned to each 1 km2 cell of the onshore-wind resource map allowed an initial selection of potential sites for wind generation. Inappropriate sites were filtered out by reference to absolute and consultation constraints including:

    Natural and cultural heritage sites;
    Aviation and radar interference areas;
    Cities, towns and villages; lakes; cells with an average slope greater than 15%.

For the remaining 1 km2 cells the lifetime production cost was calculated. This figure included the grid connection cost and, in the case of the islands, a share of the undersea cable connection.
The cells were ranked according to the lifetime production cost and groups of the 'cheapest' (for example the cheapest 1,500 MW out of all of the onshore wind generating capacity) were selected for scenario calculations. Time-series of wind-generated power were needed for all potential onshore sites.
The first stage of this process was to use the WindFarmer program from Garrad Hassan to compute a flow matrix for each cell of interest. This matrix transforms 'input' wind-speeds and directions at the associated met station (at 10 m agl) to 'output' wind-speeds (at 80 m agl) at the 1 km2 cell.
The time-series of wind-speed for each selected cell was then generated from the Met Office time-series data.

Wind-speed time series were converted to power time series using the power curve shown in Figure 3.3. The generated power for each cell had to be reduced in order to allow for the following factors.




Wave power formula

In deep water where the water depth is larger than half the wavelength, the wave energy flux is :

 Wave_power_formula

 Elliptical_trajectory_on_ripples

The above formula states that wave power is proportional to the wave period and to the square of the wave height. When the significant wave height is given in meters, and the wave period in seconds, the result is the wave power in kilowatts (kW) per meter of wave front length.

 

Example:
Consider moderate ocean swells, in deep water, a few kilometers off a coastline, with a wave height of 3 meters and a wave period of 8 seconds. Using the formula to solve for power, we get around 36 kilowatts of power potential per meter of coastline.

Wave_power_formula_example

Wave_schematic_power_formula


In major storms, the largest waves offshore are about 15 meters high and have a period of about 15 seconds. According to the above formula, such waves carry about 1.7 MW/m of power across each meter of wave front.

 wave_energy_buoy_coast_conceptual_wave_park

Wave energy and wave energy flux

In a sea state, the average energy density per unit area of gravity waves on the water surface is proportional to the wave height squared, according to linear wave theory:

Tidal_wave_formula

Where E is the mean wave energy density per unit horizontal area (J/m2), the sum of kinetic and potential energy density per unit horizontal area. The potential energy density is equal to the kinetic energy, both contributing half to the wave energy density E, as can be expected from the equipartition theorem.
In ocean waves, surface tension effects are negligible for wavelengths above a few decimetres.

 wraspaGA_

An effective wave power device captures as much as possible of the wave energy flux. As a result the waves will be of lower height in the region behind the wave power device.
Also some inside “Underwater rivers “like recently that which was discover between Mediterranean See and Black See maybe can be used on deep underwater, if the stream is very fast to generate energy…..




But is it viable?

Wavegen says that there could be sufficient recoverable wave power around the UK to generate enough power to exceed domestic electricity demands.
Furthermore, renewable energy supporters say some research suggests that less than 0.1% of the renewable energy within the world's oceans could supply more than five times the global demand for energy - if it could be economically harvested.
That would probably involve large-scale wave plants in near-shore or off-shore environments, a technology still being developed.

 

ave_power_station_schematik_design


However, large-scale on-shore wave power generating stations could face similar problems to those encountered by some windfarm projects, where opposition has focused on the aesthetic and noise impact of the machinery on the environment.
Wave power supporters say that the answer lies not in huge plants but in a combination of on-shore generation and near-shore generation (using a different technology) focused on meeting local or regional needs.

 

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Sources:
http://eecs.engr.oregonstate.edu/wesrf/images/Overview%20of%20Wave%20Energy%20Activities%20at%20OSU.pdf
Oregon state University (Schematic of Pic “Conceptual Wave Park)
http://www.douglaselectric.com/resources/
http://www.boem.gov/Renewable-Energy-Program/Regulatory-Information/Index.aspx#Programmatic_Environmental_Impact_Statement_%28PEIS%29
http://celebrating200years.noaa.gov/magazine/wave_energy/conceptual_wave_park.html
http://www.mech.ed.ac.uk/research/wavepower/0-Archive/EWPP%20archive/1976%20Leishman%20and%20Scobie%20NEL.pdf
http://www.siemens.co.uk/events/pool/home/EFEF/thefutureofenergy.pdf
http://news.bbc.co.uk/2/hi/science/nature/1032148.stm
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