Wave energy_MR YORN THORT-EEE-ITC-Cambodia

Institute of Technology of CambodiaDepartment Electrical and Energy Engineering

Topic: Wave power

Lecturer: ETH OudayaStudents: VORN Rithy e20120795YA Phalkun e20140873YAV Leakhena e20140874YORN Thort e20120815

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ContentI. Introduction

II. History

III. Resource

IV. Variability

V. Wave Motion

VI. The Velocity of Ocean Waves

VII. Wave energy and power

VIII. Ocean Wave Energy Technology

IX. About Pelamis

X. Case study

XI. Advantages and disadvantages of Wave power

XII. Conclusion

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II. Introduction

Wave energy or wave power is essentially power drawn from waves. When wind blows across the sea surface, it transfers the energy to the waves.

They are powerful source of energy and the energy output is measured by wave speed, wave height, length of wave and water density

The more strong the waves, the more capable it is to produce power. The captured energy can then be used for electricity generation.

Successful and profitable use of wave energy on a large scale only occurs in a few regions around the world. The places include the states of Washington, Oregon and California and other areas along North America’s west coast. This also includes the coasts of Scotland Africa and Australia.

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I. History

The first known patent to use energy from ocean waves dates back to 1799, and was

filed in Paris by Girard and his son. An early application of wave power was a device

constructed around 1910 by Bochaux-Praceique to light and power his house

at Royan, near Bordeaux in France. Modern scientific pursuit of wave energy was pioneered by Yoshio Masuda's

experiments in the 1940s. He has tested various concepts of wave-energy devices at

sea. Among these was the concept of extracting power from the angular motion at the

joints of an articulated raft, which was proposed in the 1950s by Masuda.

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III. Resource

The passage of wind over the surface of the sea results in the gradual transfer of energy into the water to produce waves. When wind blows across the surface of the water strongly enough it creates waves.

Wind power typically has densities in the range 1.2 – 1.8 kW/ . Waves with a typical power density of 50 kW per meter of wave front or crest length.

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IV. Variabilities

The wave resource, not unlike the wind resource on which it depends, also varies on a day - to - day and season - by - season basis; in general wave conditions are more energetic in the winter than in the summer.

For example, about half of the annual wave power at all UK sites occurs during the winter months of December, January and February, as shown in Figure 2.22.

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Figure 07: Average monthly wave power in the UK. Average monthly wind power capacity factor [15] is shown for reference purposes. (Reproduced from Sinden, G.E., 2007, DPhil Thesis with permission of Environmental Change Institute, Oxford University Centre for the Environment).

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V. Wave motion

The circular particle motion has an amplitude that decreases exponentially with depth and becomes negligible for D< /2.

1). The surface waves are sets of unbroken sine waves of irregular wavelength, phase and direction.

2). The amplitudes of the water particle motions decrease exponentially with depth. At a depth of below the mean surface position, the amplitude is reduced to 1/e of the surface amplitude (e = 2.72, base of natural logarithms). At depths of the motion is negligible, being less than 5% of the surface motion.

3). The amplitude a of the surface wave is essentially independent of the wave length , velocity C or period T of the wave, and depends on the history of the wind regimes above the surface. It is rare for the amplitude to exceed one-tenth of the wavelength.

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Figure 08: Particle motion in water waves. (a) Deep water, circular motion of water particles. (b) Shallow water, elliptical motion of water particles.

A particle of water in the surface has a circular motion of radius a equal to the amplitude of the wave. The wave height H from the top of a crest to the bottom of a trough is twice the amplitude: H = 2a. The angular velocity of the water particles is (radian per second).

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Figure 09: Wave characteristics.

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Figure 10: Water surface perpendicular to resultant of gravitational and centrifugal force acting on an element of water, mass m.

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Figure 11: Resultant forces on surface particules.

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Figure 12: Accelerations and velocities of a surface water particle. (a) Water surface.(b) Particle acceleration, general derivation. (c) Particle velocity.

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The surface motion is that of a travelling wave

Period of the motion

The velocity of a particle at the crest of the wave

The wave surface velocity in the x direction

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VI. The Velocity of Ocean Wavesd :The depth of the water.

g : The acceleration of gravity, 9.81 m/s2.

h: The height of the wave—the vertical distance between the through and the crest of a wave.

T : The period the time interval between two successive wave crests at a fixed point.

v : The phase velocity of the wave—the ratio between the wavelength and the period.

λ: The wavelength the horizontal distance between two successive wave crests, measured along the direction of propagation.

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Deep water , thus the wave velocity

Shallow water , thus the wave velocity

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VII. Wave energy and power

a) BasicThe elementary theory of deep water waves begins by considering a single regular wave. The particles of water near the surface will move in circular orbits, at varying phase, in the direction of propagation x.

Figure 13: Elemental motion of water, drawn to show the exponential decrease of amplitude with depth.

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• The kinetic energy per unit width of wave front per unit of wave

• Potential energy per unit width of wave per unit length

• The total energy per unit width per unit length of wave front, i.e. total energy per unit area of surface

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Figure14: Local pressure fluctuations in the wave. (a) Pressures in the wave. (b) Local displacement of water particle.

b) Power extraction from wavesThe energy is associated with water that remains at the same location when averaged overtime

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The power carried in the wave at x, per unit width of wave-front at any instant, is given by

The power carried forward in the wave per unit width across the wave front.

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Wave technologies have been designed to be installed in the nearshore,

offshore, and far offshore locations.

While wave energy technologies are intended to be installed at or near the

water's surface, there can be major differences in their technical concept

and design.

VII. Ocean Wave Energy Technologies

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VII. Ocean Wave Energy Technologies

Point absorbers

Attenuators

Overtopping devices

Terminators.

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VII. Ocean Wave Energy Technologies

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VII. Ocean Wave Energy Technologies Terminator Devices

The wave motion inside the chamber alternately compresses and decompresses the air that exists above the water level inside the chamber.

As a result, an alternating stream of high-velocity air is generated.

This airflow is driven through a duct to a turbine generator that is used to generate electricity.

The energy generating capacity of a single terminator device can be up to 1.5 MW.

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VII. Ocean Wave Energy Technologies Terminator Devices

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The Oscillating Water Column (OWC) generates electricity in a two step process. As a wave enters the column, it forces the air in the column past a turbine and increases the pressure within the column.As the wave retreats, the air is drawn back past the turbine due to the reduced air pressure on the ocean side of the turbine.Irrespective of the airflow direction, the turbine (referred to as a Wells turbine, after its inventor) turns in the same direction and drives a generator to produce electricity.

VII. Ocean Wave Energy Technologies Terminator Devices

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VII. Ocean Wave Energy TechnologiesAttenuators The segments flex at hinged joints as a

wave passes along the device. The mechanical motion of the flexing is converted to electrical energy using hydraulic motors and generators.

The electrical energy is fed down a single umbilical cable to a junction on the seabed.

Several devices can be connected together and linked to shore through a single underwater transmission cable.

The energy generating capacity of a single attenuator device can be up to 1 MW.

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VII. Ocean Wave Energy Technologies Attenuators

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Each Pelamis has three power module joined by tubular section.

Wave causes the modules and tubes to move in relation to each other.

This motion is resisted by hydraulic rams in each of joints.

The hydraulic rams pump high-pressure oil through hydraulic motors.

The hydraulic motors drive electrical generators to produce electricity.

VII. Ocean Wave Energy Technologies Attenuators

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VII. Ocean Wave Energy Technologies Point Absorbers

The rise and fall of the wave height at a single point that caused by passing waves is used to drive electromechanical or hydraulic energy converters to generate power.

This mechanical energy drives an electrical generator. The electrical energy is fed down a single umbilical cable to a junction on the seabed.

Several devices can be connected together and linked to shore through a single underwater cable. They can either float or be anchored to the sea floor.

An individual point absorber device may produce up to 11 MW of electricity.

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VII. Ocean Wave Energy Technologies

Point Absorbers

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VII. Ocean Wave Energy Technologies Overtopping Devices

• Overtopping devices generally are anchored in open water and consist of reservoirs that are filled by wave action to levels above the surrounding sea level.

The energy generating capacity of a single overtopping device can be up to 11 MW.

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IX. About PelamisPelamis wave power is a

technology that uses the motion

of ocean surface wave to create

electricity developed by the

Scottish company was

established in 1998 and had

office and fabrication facilities

in Leith Docks, Edinburgh,

Scotland.

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IX. About Pelamis Construction details

• Each Pelamis machine is of 120mts long.

• It has a diameter of 3.5 mts.

• Each Pelamis machine has three power conversion modules.

• Each machine is rated to produce 750KW

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IX. About Pelamis Production of Pelamis

PCM

SteelTubenose

Assembly

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IX. About Pelamis

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IX. About Pelamis

Operation of Pelamis wave power

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IX. About Pelamis How does it work?

• The Buoyant Moored Device works by rotating about a long linkage

• The Oscillation Water Column, water work a piston to pumps air and drive a turbine to generate power

• Machine floats on the surface of the water. The structure is secured by flexile cable fitted to the seabed

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IX. About Pelamis

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Electrical cable• Submersible ower cables

are vulnerable to damage and need to be buries into soft sediments on the ocean floor.

• XLPE insulations have proven to be an excellent alternative having no such potential hazards associated with its operation.

IX. About Pelamis

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IX. About Pelamis Wave energy Market

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X. Case Study

Project Name Okeanós: Pelamis wave energy farm PortugalProject Three P1-A Pelamis machines

Location Aguçadoura/ Póvoa de Varzim, Northern Portugal 

Installed capacity 3 * 750 kW = 2.25 MW; plans exist to extend to 30 devices (22.5 MW)

Technology Type Pelamis: Floating articulated attenuator 

Project Type/Phase Commercial contract 

Year Construction of devices terminated in 2006, later assembly and partly testing by early 2008; installation summer 2008

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XI. Advantages and disadvantages

Advantages

1) Renewable

2) Environment Friendly

3) Easily Predictable

4) Less Dependency on

Foreign Oil Cos

5) No Damage to Land

Disadvantages

1)Suitable to Certain Locations

2)Wave length

3)Noise and Visual

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VII. Conclusion

• No land requirement

• Invest installation

• Run low operation cost

• Product electricity 24 h per day

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