Wave Power

Wave power refers to the energy of ocean surface waves and the capture of that energy to do useful work, including electricity generation, desalination, and the pumping of water into reservoirs.   Wave power is a form of renewable energy.   Wave power is distinct from the diurnal flux of tidal power and the steady gyre of ocean currents.   Wave power generation is not a widely employed technology, with the world's first commercial wave farm, the Aguçadora Wave Park in Portugal, being established in 2006.   The north and south temperate zones have the best sites for capturing wave power.   The prevailing westerlies in these zones blow strongest in winter. ^{Wiki n.p.}

When an object bobs up and down on a ripple in a pond, it experiences an elliptical trajectory.   In general, large waves are more powerful.   Specifically, wave power is determined by wave height, wave speed, wavelength, and water density.   Wave size is determined by wind speed and fetch, which is the distance over which the wind excites the waves, and by the depth and topography of the seafloor, which can focus or disperse the energy of the waves.   A given wind speed has a matching practical limit over which time or distance will not produce larger waves.   This limit is called a "fully developed sea."   Wave motion is highest at the surface and diminishes exponentially with depth; however, wave energy is also present as pressure waves in deeper water.   The potential energy of a set of waves is proportional to wave height squared times wave period, which is the time between wave crests.   Longer period waves have relatively longer wavelengths and move faster.   The potential energy is equal to the kinetic energy that can be expended.   Wave power is expressed in kilowatts per meter at a specific location. ^{Wiki n.p.}

Wave power devices are generally categorized by the method used to capture the energy of the waves.   They can also be categorized by location and power take-off system.   Method types are point absorber or buoy; surfacing following or attenuator; terminator, lining perpendicular to wave propagation; oscillating water column; and overtopping.   Locations are shoreline, nearshore and offshore.   Types of power take-off include: hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator.   Some of these designs incorporate parabolic reflectors as a means of increasing the wave energy at the point of capture. ^{Wiki n.p.}

PowerBuoy technology which consists of modular, ocean-going buoys. The rising and falling of the waves moves the buoy-like structure creating mechanical energy which is converted into electricity and transmitted to shore over a submerged transmission line.   A 40kW buoy has a diameter of 12 feet and is 52 feet long, with approximately 13 feet of the unit rising above the ocean surface.   Using the three-point mooring system, they are designed to be installed one to five miles offshore in water 100 to 200 feet deep.     The sections of the device articulate with the movement of the waves, each resisting motion between it and the next section, creating pressurized oil to drive a hydraulic ram which drives a hydraulic motor.   Wave energy converter large "arms" focus waves up a ramp into an offshore reservoir. The water returns to the ocean by the force of gravity via hydroelectric generators. ^{Wiki n.p.}

The challenges of wave power are efficiently converting wave motion into electricity.   Wave power is available in low-speed, high forces and motion is not in a single direction.   Most readily-available electric generators like to operate at higher speeds with lower input forces, and they prefer to rotate in a single direction.   Constructing devices that can survive storm damage and saltwater corrosion.   Likely sources of failure include seized bearings, broken welds, and snapped mooring lines. Knowing this, designers may create prototypes that are so overbuilt that materials costs prohibit affordable production. ^{Wiki n.p.}

Salter's Edinburgh Duck, continues to be the machine against which all others are measured. In small scale controlled tests, the Duck's curved cam-like body can stop 90% of wave motion and can convert 90% of that to electricity. While it continues to represent the most efficient use of available material and wave resources, the machine has never gone to sea, primarily because its complex hydraulic system is not well suited to incremental implementation, and the costs and risks of a full-scale test would be high. Most of the designs being tested currently absorb far less of the available wave power, and as a result their Mass to Power Ratios remain far away from the theoretical maximum. ^{Wiki n.p.}

Wave power could yield much more energy than tidal power.   Tidal dissipation (friction, measured by the slowing of the lunar orbit) is 2.5 terawatts.   The energy potential of waves is certainly greater, and wave power can be exploited in many more locations.   Countries with large coastlines and strong prevailing winds could produce 5% or more of their electricity from wave power.   Excess capacity, a problem common with variable energy sources, could be used to produce hydrogen or smelt aluminum. ^{Wiki n.p.}

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