Wave Power Conversion Systems for Electrical Energy Production

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A. Leão Rodrigues

Faculty of Science and Technology of Nova University of Lisbon

[email protected]

March 2008

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Wave energy is the capacity of the waves for doing work. It is a renewable energy. Ocean waves are generated by the influence of the wind on the ocean surface.

OutlineOutline

• Origin of Sea WavesOrigin of Sea Waves• Sea Wave CharacteristicsSea Wave Characteristics• Power Associated to a Sea WavePower Associated to a Sea Wave• Resource of Wave PowerResource of Wave Power• Types of Wave Power Types of Wave Power

MechanismsMechanisms• Pelamis Energy ConverterPelamis Energy Converter• Wave Energy MarketWave Energy Market• ConclusionsConclusions

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Origin of Sea Origin of Sea WavesWaves

storm

swellwind

wave direction

fetch

Sea waves formation due to a storm

trough

Waves - The combination of forces due to the gravity, sea surface tension and wind intensity are the main factors of origin of sea

waves. Fetch - distance over which the wind excites the waves

To distances far from the fetch, sea waves have a regular shape and the phenomenon is called swell.

Water particle v

v

v

v

Sea Wave

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Sea Wave CharacteristicsSea Wave Characteristics

Tv

crest

crest

trough

H

wavelength - distance between two consecutive crests, or two consecutive troughs

height H - distance crest to trough. It is proportional to wind intensity and its duration.

wave period T - time in seconds needed for the wave travel the wavelength

frequency f = 1/T - indicates the number of waves that appears in a given position.

wave speed –The ratio wavelength/period or v = /T = f.

declivity – the ratio /2H

When this value is greater than 1/7 the wave becomes unstable and vanishes.In deep water, the energy in waves can travel for thousands of miles until that energy is finally dissipated on distant shores.

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Power Associated to a Sea Power Associated to a Sea WaveWave

The power associated with a wave of wavelength and height H and a front b is given by

bgHP 2

2

1

H

b

Power per metre (b = 1 m) of front wave is approximately

When wave height is doubled then generates four times as much power.

20.5 P H T W m

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The world resource of wave power is estimated in about 2 TW.

Resource of Wave Resource of Wave PowerPower

Europe represents about 16% of the global wave power resource (320 GW)

Only about 10 to 15% of the global estimated resource can be converted in electrical energy.

Equator

Global wave power distribution in kW/m

Increased wave activity is found between the latitudes of 30° and 60°

on both hemispheres

mkW THP 25.0

Height (m) Period (s)

A good wave have ~50 kW/m

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A r e a s f o r d e v e l o p m e n t o f w a v e e n e r g y f a r m s :

A r e a s f o r d e v e l o p m e n t o f w a v e e n e r g y f a r m s :

A b o u t 3 3 5 k m o f t h e P o r t u g u e s e w e s t c o a s t l i n e a r e p o t e n t i a l l y a v a i l a b l e t o w a v e e n e r g y u t i l i z a t i o n

R e s t r i c t e d a r e a s o r w i t h e v e n t u a l c o n f l i c t o f u s e s :

5000 MW

Resource of Wave Resource of Wave Power in Power in Portuguese coastPortuguese coast

Povoa do Varzim

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Types of Wave Power Types of Wave Power MechanismsMechanismsThe sea wave’s motion can be converted into

mechanical energy by using proper wave power mechanisms

Shoreline

Nearshore

Offshore

• oscillating column of water

• underwater pneumatic systems

• wave dragon system

• oscillating bodies system.

lying on the bottom of the sea

on sea level.

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oscillating column of water systems

Shoreline mechanisms

Oscillating column of water system

turbine Wells

asynchronous generator

Generator/rectifier air turbine group

air turbine/generator

airflow

breakwater

hydraulic pump

Concrete boxpendulum flap

wave

Pendulum system

converter

Wells turbine

double fed wound rotor induction generator

~

grid

wind

Oscillating column of water – Pico Island, Azores

0,35

0,30

0,25

0,20

0,15

0,100,0 1,0 2,0 3,0 4,0 5,0

Rendimento

Ângulo de calagem das pás

Sem válvula de alívio

Com válvula em paralelo

Com válvula em série

Air output

turbine Wells

Wave

Structure

Parallel valveGenerator Turbine

Series valve

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underwater pneumatic systems

Nearshore

Wave and Roller (USA) 13 Wave and Roller (USA) 13 kWkW

2 MW pneumatic systems 2 MW pneumatic systems (Holand)(Holand)

Archimedes Wave Archimedes Wave SwingSwing

shaft connected to the buoy

Linear Linear generatorgenerator

fixed coil

permanent magnet

Power Buoy (USA) 40 kWPower Buoy (USA) 40 kW

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Offshore mechanisms

Salter’s Duck system

Floating cylinder

oscillating movement converter

electric generator

waves

Escone

sea level

under sea

This converter unit, called Escone, after his inventor Esko Raikano, is the heart of the system and converts the reciprocating motion to a rotating shaft connected direclty to a generator for generating electrical energy with high

efficiency.

Bristol cylinder for wave energy extraction

One of the first methods to extract mechanical energy from the waves was invented in the 1970s by Professor Stephen Salter of the University of Edinburgh, Scotland, in response to the Oil Crisis. It can be moored, to distances of 80 km of the cost. The cam rotates about its axis and is shaped to minimize back-water pressures.

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Pelamis ConverterPelamis Converter

Profile view Top view

Sea snake

Pelamis

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Some aspects of Pelamis Some aspects of Pelamis constructionconstruction

Rolling the steel plate Steel tubes of 3.5 m in diameter

TransportationArticulation

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Pelamis Pelamis layoutlayout

Power module of 250 kVAPower transformer de 950 kVA 6.6/15 kV Three phase cable 15 kV

Three phase cable 15 kV

D/3

T D = 3.5 m

Articulation Power Module

120 m ~

30 m 5 m

Nose P-750

Articulation

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Hydraulic arm

High pressure container

Motor/generator set

Distributor

Reservoir

Vertical articulated axis

Horizontal articulated axis

Power modulePower module

Inside view of the power module

Efficiency = 35 %

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Electric generator

Gas under pressure

HP

Valve 1

Hydraulic motor

Hydraulic arm 1

Hydraulic arm 2

Fluid under pressure

Reservoir

LP

force

force

Valve 2

High pressure

Low pressure

Hydraulic circuitHydraulic circuit

Hydraulic arms

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Pelamis wave energy converter of 750 kW

Wave farm of Aguçadora of 2.25 MW

Association of Pelamis units in a total of 30 MW

(waiting for legislation)

2100 m

600 mof

PelamisPelamisWave direction

Pelamis

Seabed

Anchorage

Pelamis anchorage to the seabed

Flexible cable

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Pelamis installationPelamis installation

Total power = 2.25 MW. (3 units of 750 kW)

15 kV

2001 2002 2003 3 year average

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

150

125

100

75

50

25

0

Wave Seasonal Variability

Ave

rage

inci

dent

pow

er (k

W/m

)

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Costs distribution for a wave power plant

Wave Wave EnergyEnergy MarketMarket

mechanical and electrical equipment

49%

structures

27%

assemblage

13%

grid connectionproject management

2%

5%

anchorage

4%

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ConclusionsConclusions Wave energy is not expensive to operate and maintain, no fuel is needed

and no waste is produced. However, it depends on the intensity of the waves and needs a suitable site where waves are consistently strong. The infrastructure must be able to withstand very rough weather.

Wave power 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. If this system prove to be economically possible, only 0.1% of the renewable energy within the world's oceans could supply more than five times the global demand for energy.

The Pelamis Wave Energy Converter is a revolutionary concept resulting from many years of engineering development. It was the world’s first commercial scale machine to generate electrical energy into the grid from offshore wave energy and the first to be used in commercial wave park projects. In Portugal, Pelamis System is now proving to be successful.