Wave Power

1. 1
A.Leão Rodrigues
Faculty of Science and Technology of Nova
University of Lisbon
[email protected]
March 2008

2. 2
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 MechanismsTypes of Wave Power Mechanisms
• Pelamis Energy ConverterPelamis Energy Converter
• Wave Energy MarketWave Energy Market
• ConclusionsConclusions

3. 3
Origin of Sea WavesOrigin of Sea Waves
storm
swell
wind
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

4. 4
Sea Wave CharacteristicsSea Wave Characteristics

T
v


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.

5. 5
Power Associated to a Sea WavePower Associated to a Sea Wave
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.
 
2
0.5 P HTWm

6. 6
The world resource of wave power is
estimated in about 2 TW.
Resource of Wave PowerResource of Wave Power
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 
2
5.0
Height (m)Period (s)
A good wave have ~50 kW/m

7. 7
5000 MW

8. 8
Types of Wave Power MechanismsTypes of Wave Power Mechanisms
The 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.

9. 9
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 box
pendulum
flap
wave
Pendulum system
converter
Wells
turbine
double fed wound rotor induction generator
~
grid
wind

10. Oscillating column of water – Pico Island, Azores
0,35
0,30
0,25
0,20
0,15
0,10
0,0 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

11. 11
underwater pneumatic systems
 Nearshore
Wave and Roller (USA) 13 kWWave and Roller (USA) 13 kW
2 MW pneumatic systems (Holand)2 MW pneumatic systems (Holand)
Archimedes Wave SwingArchimedes Wave Swing
shaft connected to
the buoy
Linear generatorLinear generator
fixed
coil
permanent
magnet
Power Buoy (USA) 40 kWPower Buoy (USA) 40 kW

12. 12
 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.

13. 13
Pelamis ConverterPelamis Converter
Profile view Top view
Sea snake
Pelamis

14. 14
Some aspects of Pelamis constructionSome aspects of Pelamis construction
Rolling the steel plate Steel tubes of 3.5 m in diameter
TransportationArticulation

15. 15
Pelamis layoutPelamis layout
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

16. 16
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 %

17. 17
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

18. 18
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
PelamisPelamis
Wave
direction
Pelamis
Seabed
Anchorage
Pelamis anchorage to the seabed
Flexible cable

19. 19
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
A
v
erag
e
i
n
cid
e
nt po
we
r
(k
W
/m
)

20. 20
Costs distribution for a wave power plant
Wave Wave EnergyEnergy Market Market
mechanical and electrical equipment
49%
structures
27%
assemblage
13%
grid connection
project
management
2%
5%
anchorage
4%

21. 21
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.