Wave Power EEES

8/4/2019 Wave Power EEES

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Wave power is the transport ofenergy by ocean surface waves, and the capture of that energy to do usefulwork for example forelectricity generation, water desalination, or thepumping of water (into reservoirs).

Wave power is distinct from the diurnal flux oftidal powerand the steady gyre ofocean currents. Wave

power generation is not currently a widely employed commercial technology although there have been

attempts at using it since at least 1890. In 2008, the first experimental wave farm was opened in Portugal, at

the Aguadoura Wave Park.

PHYSICAL CONCEPT

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. Both air

pressure differences between the upwind and the lee side of a wave crest, as well as friction on the water

surface by the wind, making the water to go into the shear stress causes the growth of the waves.[3]

Wave height is determined by wind speed, the duration of time the wind has been blowing, fetch (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. When this limit has been reached the sea is said to be "fully

developed".

In general, larger waves are more powerful but wave power is also determined by wave speed, wavelength,

and waterdensity.


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Motion of a particle in an ocean wave.

A = At deep water. The orbitalmotion of fluid particles decreases rapidly with increasing depth below the

surface.

B = At shallow water (ocean floor is now at B). The elliptical movement of a fluid particle flattens with

decreasing depth.

1 = Propagation direction.

2 = Wave crest.

3 = Wave trough


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Wave power formulaIn dee wate whe ethe wate de th isla e than hal thewa elength, the wa eene gy fl is

1]

with Pthe wa eene gy fl pe unit of wa e-c estlength, Hm0thesignificant wa e height, Tthe wa epe iod, the wate densityand gtheaccele ation by gra ity. Theabove formulastatesthat wave poweris

proportionalto the wave period and to thesquare ofthe wave height. When thesignificant wave heightisgiven in meters, and the wave period in seconds, the resultisthe wave powerin kilowatts (kW) permeter ofwavefrontlength.

[4][5][6]

Example:Considermoderate ocean swells, in deep water, a few kilometers offacoastline, with a waveheight of 3 metersand a wave period of 8 seconds. Using the formulato solve for power, we get

meaning thereare 36 kilowatts of power potential permeter ofcoastline.

In majorstorms, thelargest waves offshoreareabout 15 meters high and havea period ofabout 15 seconds.According to theabove formula, such wavescarry about 1.7 MW of poweracrosseach meter of wavefront.

An effective wave power devicecapturesasmuch as possible ofthe waveenergy flux. Asa resultthe waveswill be oflower heightin the region behind the wave power device.


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Wave energy and wave energy fluxIn aseastate, theaverageenergy density per unitarea ofgravity waves on the watersurfaceis proportionalto the wave heightsquared, according to linear wavetheory:

whereEisthemean waveenergy density per unit horizontalarea (J/m ), thesum ofkineticandpotentialenergy density per unit horizontalarea. The potentialenergy density isequalto the kineticenergy,

[3]both

contributing halfto the waveenergy density E, ascan beexpected fromtheequipartition theorem. In ocean

waves, surfacetension effectsare negligible for wavelengthsabovea few decimetres.

Asthe waves propagate, theirenergy istransported. Theenergy transport velocity isthe group velocity. Asaresult, the waveenergy flux, through a vertical plane of unit width perpendicularto the wave propagationdirection, isequalto:

[9][3]

with cgthe group velocity (m/s). Dueto thedispersion relation for water waves undertheaction of gravity,

the group velocity depends on the wavelength , orequivalently, on the waveperiodT. Further, thedispersion relation isa function ofthe water depth h. Asa result, the group velocity behaves differently inthelimits of deep and shallow water, and atintermediate depths:


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Oce W e Ener y TechnologiesA variety of technologies have been proposed to capture the energy from waves. ome of the more

promising designs are undergoing demonstration testing at commercial scales.

Wave technologies have been designed to be installed in nears ore, o s ore, and ar o s ore locations.

The OC Alternative Energy Programmatic EI is concerned primarily with offshore and far offshore wave

technologies. Offshore systems are situated in deep water, typically of more than 40 meters (131 feet).

While all wave energy technologies are intended to be installed a or near e wa er's sur ace, they differ

in their orientation to the waves with which they are interacting and in the manner in which they convert the

energy of the waves into other energy forms, usually electricity. The following wave technologies have been

the target of recent development.

Termina or evices extend perpendicular to the direction of wave travel and capture or reflect the power of

the wave. These devices are typically onshore or nearshore; however, floating versions have been designed

for offshore applications. The oscilla ing wa er column is a form of terminator in which water enters

through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured

water column to move up and down like a piston to force the air though an opening connected to a turbine.

A point absorber is a floating structure with components that move relative to each other due to wave

action (e.g., a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical

or hydraulic energy converters.


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Point absorber wave farm

Rendition of a Wave Farm Made Up of Permanent Magnet Linear

Generator Buoys


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Attenuators are long multisegment floating structures oriented parallelto the direction of the waves. The differing heights of waves along the

length of the device causes flexing where the segments connect, and

this flexing is connected to hydraulic pumps or other converters.

Overtopping evices have reservoirs that are filled by incoming waves

to levels above the average surrounding ocean. The water is then released, and gravity causes it to fall back

toward the ocean surface. The energy of the falling water is used to turn hydro turbines. pecially built

seagoing vessels can also capture the energy of offshore waves. These floating platforms create electricityby funneling waves through internal turbines and then back into the sea.

These are descriptions of some wave power systems:

yIn the United tates, the Pacific Northwest Generating Cooperative is funding the building of acommercial wave power park at Reedsport, Oregon.

[22]The project will utilize the PowerBuoy

technology Ocean Power Technologies which consists of modular, ocean going buoys. The rising and

falling of the waves moves hydraulic fluid with the buoy; this motion is used to spin a generator, and

the electricity is transmitted to shore over a submerged transmission line. A 150 kW buoy has a

Attenuator Wave Energy Device


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diameter of 36 feet (11 m) and is 145 feet (44 m) tall, with approximately 30 feet of the unit risingabove the ocean surface. Using a three point mooring system, they are designed to be installed one to

five miles (8 km) offshore in water 100 to 200 feet (60 m) deep.

y An example of a surface following device is the Pelamis Wave Energy Converter. The sections of thedevice 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. The machine

is long and narrow (snake like) and points into the waves; it attenuates the waves, gathering more

energy than its narrow profile suggests. Its articulating sections drive internal hydraulic generators

(through the use of pumps and accumulators).

T e r t t e Pel mis m c i e rsti t r w ve t t e A c r W ve


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yWith the Wave Dragon wave energy converter large wing reflectors focus waves up a ramp into anoffshore reservoir. The water returns to the ocean by the force of gravity via hydroelectric generators.

y The Anaconda Wave Energy Converteris in the early stages of development by UK companyCheckmate eaEnergy. The concept is a 200 metre long rubber tube which is tethered underwater.

Passing waves will instigate a wave inside the tube, which will then propagates down its walls, driving

a turbine at the far end.

y The A uaBuOY is a technology developed by Finavera Renewables Inc. In 2009 Finavera Renewablessurrendered its wave energy permits from FERC. In July 2010 Finavera announced that it has entered

into a definitive agreement to sell all assets and intellectual property related to the A uaBuOY wave

energy technology to an undisclosed buyer.

y The Flan ea is a so called "point absorber" buoy, developed for use in the southern North eaconditions. It works by means of a cable that due to the bobbing effect of the buoy, generates

electricity.

y The eaRaser, built by Alvin mith, uses an entirely new techni ue (pumping) for gathering the waveenergy.

y A device called CETO, currently being tested offFremantle, Western Australia, consists of a singlepiston pump attached to the sea floor, with a float tethered to the piston. Waves cause the float to rise

and fall, generating pressurized water, which is piped to an onshore facility to drive hydraulic

generators or run reverse osmosis water desalination.

y Another type of wave buoys, using special polymeres, is being developed by RI[37][38]

y Wavebob is an Irish Company who have conducted some ocean trials.y The Oyster wave energy converteris a hydro electric wave energy device currently being developed

by A uamarine Power. The wave energy device captures the energy found in nearshore waves and

converts it into electricity. The systems consists of a hinged mechanical flap connected to the seabed at


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around 10m depth. Each passing wave moves the flap which drives hydraulic pistons to deliver highpressure water via a pipeline to an onshore turbine which generates electricity. In November 2009, the

first full scale demonstrator Oyster began producing power when it was launched at the European

Marine Energy Centre (EMEC) on Orkney.

y Ocean Energy have developed the OE buoy which has completed ( eptember 2009) a 2 year sea trialin one uarter scale form. The OE buoy has only one moving part.

y The Lysekil Project is based on a concept with a direct driven linear generator placed on the seabed.The generator is connected to a buoy at the surface via a line. The movements of the buoy will drive

the translator in the generator. The advantage of this setup is a less complex mechanical system with

potentially a smaller need for maintenance. One drawback is a more complicated electrical system.


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yAn Australian firm, Oceanlinx, is developing a deep water technology to generate electricity from,ostensibly, easy to predict long wavelength ocean swell oscillations. Oceanlinx recently began

installation of a third and final demonstration scale, grid connected unit nearPort Kembla, near

ydney, Australia, a 2.5 MWe system that is expected to go online in early 2010, when its power will

be connected to the Australian grid. The companies much smaller first generation prototype unit, in

operation since 2006, is now being disassembled.[11]

y An Israeli firm, DEENERGY LTD., has developed a breakwater based wave energy converter. Thisdevice is close to the shore and utilizes the vertical motion of buoys for creating an hydraulic pressure,

which in turn operates the system s generators. .D.E. is currently building a new 250 kWh model in

the port ofJaffa, Tel Aviv and preparing to construct it s standing orders for a 100mWh power plants

in the islands ofZanzibarand Kosrae, Micronesia.

y A Finnish firm, AW Energy Oy, is developing the WaveRoller device: that is a plate anchored on thesea bottom by its lower part. The back and forth movement of surge moves the plate. The kinetic

energy transferred to this plate is collected by a piston pump.y The United tates Air Force Academy is developing a long ocean wave cancelling electric generator

that simulations and small scale tests show can capture more than 95% of the energy of long ocean

waves. Using a cycloidal turbine to convert wave power into lift, the turbine takes the energy of

flowing water and converts it through lift to rotational energy. A rotating shaft can generates

electricity. The initial concept came from the so called Voith chneider propeller, which is used to

power tugboats.


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IWAVEWAVE ENERGY DEVICE

It is a floating device tethered with chains to piles driven to ocean bottom. The wave action raises the heavy

partially buoyant piston that drives the overhead crankshaft by half turn. The receding wave drops the piston

completing the balance half turn. One revolution is obtained for every wave. Using gear box and generatorthe current is produced continuously.


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Ad ntages Of IWAVE1.It can be made a floating device tethered with cables/chains to piles driven to the sea bottom.2.It can be positioned approximately 500 M from the seashore where the waves rise up above the sea

level.

3.It can be moved to places where adequate wave energy is available.4.The equipmentis economical to produce, install and maintain.5.Cost of energy produced is cheap and competitive to conventional sources of energy.6.Directly converts kinetic and potential energy in the wave to mechanical and electrical energy.7.In addition the device will be eligible for carbon credits that can be traded in the international

market.

8.The device is eligible for accelerated depreciation in the hands ofthe buyer.9.A 500 KWH unithaving 2 nos X 250 KW on either side could be factory made and installed in sea.

Wave farms

The Aguadoura Wave Farm was the worlds first wave farm. It was located 5 km (3 mi) offshore near

Pvoa de Varzim north ofOporto in Portugal. The farm was designed to use three Pelamis wave energy

converters to convert the motion of the ocean surface waves into electricity, totalling to 2.25MW in total

installed capacity. The farm first generated electricity in July 2008[49]

and was officially opened on the 23rd

of eptember 2008, by the Portuguese Minister ofEconomy.[50][51]

The wave farm was shut down two


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months after the official opening in November 2008 as a result of the financial collapse of Babcock &Brown due to the global economic crisis. The machines were off site at this time due to technical problems,

and although resolved have not returned to site without financial backing.[52]

A second phase of the project

planned to increase the installed capacity to 21MW using a further 25 Pelamis machines[53]

is in doubt

following Babcock s financial collapse.

Funding for a 3MW wave farm in cotland was announced on 20 February 2007 by the cottish Executive,

at a cost of over 4 millionpounds, as part of a 13 million funding package formarine power in cotland.The first of 66 machines was launched in May 2010.

[54]

Funding has also been announced for the development of a Wave hub off the north coast of Cornwall,

England. The Wave hub will act as giant extension cable, allowing arrays of wave energy generating devices

to be connected to the electricity grid. The Wave hub will initially allow 20MW of capacity to be connected,

with potential expansion to 40MW. Four device manufacturers have so far expressed interest in connectingto the Wave hub.[55][56]

The scientists have calculated that wave energy gathered at Wave ub will be enough to power up to 7,500

households. avings that the Cornwall wave power generator will bring are significant: about 300,000 tons

of carbon dioxide in the next 25 years.[57]

A CETO wave farm off the coast of Western Australia has been operating to prove commercial viabilityand, after preliminary environmental approval, is poised for further development


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Challenges

y There is a potential impact on the marine environment. Noise pollution, for example, could havenegative impactif not monitored, althoughthe noise and visible impact of each design varies

greatly.[5]

y In terms of socio-economic challenges, wave farms can resultin the displacement of commercial andrecreational fishermen from productive fishing grounds, can change the pattern of beach sandnourishment, and may representhazards to safe navigation.

[48]

y Waves generate about 2,700 gigawatts of power. Ofthose 2,700 gigawatts, only about 500 gigawattscan be captured withthe currenttechnology.

[20]

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Wave Power EEES