1

Trondheim, februar 2005 johannes.falnes@phys.ntnu.no http://www.phys.ntnu.no/~falnes

HAVBØLGJE-ENERGI

Forelesningar vedJohannes Falnes

(6 timar i februar 2005)

• NTNU• Noregs teknisk-naturvitskaplege universitet

• Fag ENERGI FRÅ VIND OG HAVSTRAUM• (NTNU-fag 4175)

Ocean waves as energy resource

JF 2004-10

• Ocean waves represent a clean and renewable energy source,come into being by conversion of wind energy when windsblow along the sea surface. Wind energy, in turn, originatesfrom solar energy, because sun heating produces low pressuresand high pressures in the atmosphere. In either of these twoenergy conversions, energy flow becomes intensified.

• Just below sea surface the average wave-power level (energytransport) is typically five times denser than the wind energytransport 20 m above the water, and 10 to 30 times denser thanaverage solar energy intensity.

• This fact gives good prospects for development of feasiblecommercial methods for utilisation of wave energy. Thus wavesmay, in future, provide substantial contributions to the energy

supply of many coastal nations.

JF 2004-10

•

••• Wave energy: 2 - 3 kW/m2

Ocean waves represent animpressive energy resource.

• Average energy intensity:

• Solar energy: 100 - 200 W/m2

•

•• Wind energy: 400 - 600 W/m2

What is a wave?• Everyone has seen waves on lakes or

oceans. Waves are actually a form ofenergy. Energy, not water, moves along theocean's surface. The water particles onlytravel in small circles as a wave passes.

Wave direction

Snapshot of the water surface at a certain instant:

ØTS+J.F.&J.H.

How to describe a wave

Wave direction

Snapshot of the water surface at a certain instant:

Wavelength L

Wave height H

Amplitude ACrest

TroughJ.F.&J.H.

Surface elevation versus time

At a fixed position in space:

Wave period T

Time

Frequency f = 1 / T J.F.&J.H.

2

Wind waves and swells

•Waves generated by wind are called windwaves. When the waves propagate outsidetheir region of generation, they are calledswells [in Norwegian: dønningar]. Wherethe water is deep, swells can travel verylarge distances, for instance across oceans,almost without loss of energy.

J.F.&J.H.

What happens underwater?

In deep water the watermolecules travel invertical circles (while inshallow water themotion is elliptical)This motion of waterparticles also happensunderwater, but theparticle velocity andthereby the circle radiusdecrease quickly as yougo deeper in the water.

Wave direction

ØTS+J.F.&J.H.

Wave velocities

• The energy in thewaves travel with thegroup velocity cg.The individual wavestravel faster - they areborn on the rear endof the group, and theydie in the front end.On deep water thisphase velocity is twicethe group velocity: Tgcc g π2

2 == = (1.56 m/s2) · TJ.F.&J.H.

Time step 1

Time step 2

Time step 3

Swells propagating across the Pacific

• Since the groupvelocity is proportionalto the period, low-frequency waves movefaster away from astorm centre than high-frequency waves. Thefigure shows thesituation 4 days after astorm with centrelocated at 170º eastand 50º south.

T = 20 s

T = 18 s

T = 16 s

T = 14 s

T = 12 s

T = 10 s

Period

-10

-20

-30

-40

180 190 200Source: OCEANOR, Norway

J.F.&J.H.

Energy content of waves• For a sinusoidal wave of height H, the

average energy E stored on a horizontalsquare metre of the water surface is:

• Half of this is potential energy due to water liftedfrom wave troughs to wave crests. The remaininghalf is kinetic energy due to the motion of the water.

2HkE E=

2s/mkW 52m:Example ⋅=⇒= EH

kE = ρ g / 8 = 1.25 kW ·s/m4

ρ = mass density of sea water ≈ 1020 kg/m3

g = acceleration of gravity ≈ 9.8 m/s2

J.F.&J.H.

Energy transport in waves• The energy transport per metre width of

the wave front is

2THkJ J=

kW/m402m and s10:Example

=⇒== JHT

EcJ g=

On deep water the group velocity is cg=gT/4π, which gives

kJ = ρ g2 / 32 π ≈ 1 kW/m3s

J.F.&J.H.

3

Significant wave height

The real-sea wave height parameter is the significant waveheight . It is traditionally defined as the average of the highestone third of the individual trough-to-crest heights Hi(i=1,2,3,…), and is denoted by H1/3.

3/3/21

3/1 NHHH

H N+⋅⋅⋅++=

TimeH1 H2 H3

Mean water levelJ.F.&J.H.

Average zero up-cross time Tz• The individual zero up-cross time Ti is the time interval

between two consecutive instants where the wave elevationcrosses the zero level in the upward direction. An average ofthese over a certain time provides a useful measure of thereal-sea wave period.

NTTT

T Nz

+⋅⋅⋅++= 21

Time

T1 T2 T3

J.F.&J.H.

Wave spectrum• A quantity derived from wave measurements is

the so-called energy spectrum S(f). It tells us howmuch energy is carried by the different frequencycomponents in the real-sea “mixture” of waves.For a sinusoidal wave the average stored energywas given by

• For a real sea wave we have instead

8/2HgE ρ=

16/d)( 2

0sHgffSgE ρρ ≡= ∫

∞

J.F.&J.H.

Wave energy transport in terms ofsignificant wave height

•Here Hs is the modern definition of significant waveheight, which in practice agrees quite well with ourprevious definition H1/3. Another quantity, the so-called wave energy period TJ, may be derived from thewave spectrum S( f ). The energy transport by real seawaves is now calculated by

2)2/( sJJ HTkJ = 3mkW/s5.02/ ≈Jk

16/d)( 2

0sHffS ≡∫

∞

J.F.&J.H.

A measurement example

•This time series (above) from high seashows that individual waves varygreatly in size and form. Thecorresponding energy spectrum isshown to the right. For this storm wavethe significant wave height is Hs = 8 m.

0 1 2 3 4 5 6 7 8 9 10 11 12-6

-4

-2

0

2

4

6

-6

0

50

100

150

0.0 0.1 0.2 0.3

S ( f )

Frequency [Hz]

Time [minutes]

Hei

ght

[m]

Source: OCEANOR, Norway

J.F.&J.H.

0.0 0.1 0.2 0.30

5

10

15

S ( f )

Frequency [Hz]

0

50

100

150

0.0 0.1 0.2 0.3

S ( f )

Frequency [Hz]

•These are typical energyspectra from wind-seaconditions (top) and mixedwind-sea and swell conditions(bottom).

•The swell contains lowerfrequencies (high peak) thanthe the wind waves (low peak).

•Significant wave heights: 8 m(top) and 3 m (bottom)

Real-sea spectra

J.F.&J.H.

Source: OCEANOR, Norway

4

Distribution of wave energy transport

Average wave power levels are approximate and given in kW/m of the wave front.

7030

4030

6040

4050 40

40

20

60

50

22

40

15

202440

50

74

3050

100

92

82

19

1221

23

1218

17

34

66

3414

8 8

27

84

37

9

10

20

48

81

30

11

100

67

131311

3

41

72

50

49

89

26

17

15

1725

2433

2997

7242

161113

12

10268 53

13 1014

12 18

1910

24

43

20

4341

33

J.F.&J.H.

Seasonal variation

• The average values of wave-energy transport varysomewhat from one year to next year. The valuesvary more between seasons. On the northernhemisphere, the average values for November andMay may differ by a factor of two or more. Thereis significantly more wind energy and waveenergy in winter than in summer, although it isopposite for solar energy. Because there may bewaves (swells) even in the absence of wind, waveenergy is more persistent than wind energy.

J.F.&J.H.

Seasonal variation at (57° N, 9° W )

• The chart shows theseasonal variation ofwave energy transportat a measurement siteclose to Barra in theHebrides off theScottish coast. Theannual average for theshown year was 65kW/m.

020

40

6080

100

120140

160

kW/m

Jan

Mar

May Ju

l

Sep

Nov

J.F.&J.H.

Based on WERATLAS, European WaveEnergy Atlas, 1996

• As we have seen, thewater particles move incircles with decreasingradius in the depth.Consequently, theenergy flow densitydecreases as we godeeper in the water. Infact, on deep water, 95% of the energy transporttakes place between thesurface and the depthL/4. (L is thewavelength).

J.F.&J.H.

Vertical distribution of wave-energy transport

2

4

6

8

3.0 kW/m2

2.1 kW/m210 m

Water level

H = 2 m and T = 10 s

•The first patent we knowof to utilise the energy ofocean waves dates from1799 and was filed in Parisby the Girards, father andson, who had observed thatwaves could lift very largeships.

•However, many centuriesearlier, Polynesians haddiscovered that they couldutilise ocean waves forsurfing (!).

J.F.&J.H.

• In 19th century proposals,the oscillating motion istransmitted to pumps orother suitable energyconversion machinery bymechanical means (suchas racks and pinions,ratchet wheels, ropes andlevers). The figure showsa float moving up anddown. Cog wheels (notshown) are engaged bycog rods rigidlyconnected to the float.

From a 57-page review paper in 1892 by A.W.Stahl, The utilization of the power of oceanwaves.

J.F.&J.H.

5

• At present, wave energyis widely used forpowering navigationbuoys. This is an oldidea, but it was firstsuccessfully realised in1965, after a study by theJapan Research andDevelopmentCorporation, after whicha Japanese company(Ryokuseisha) producedabout 1200 buoys forworld-wide use.

Front page of a 1901 issue of the Norwegianchildren’s magazine Magne. It talks about“Electrical light buoys” for navigation.J.F.

&J.H.

•An early practicalapplication of wave powerwas a device constructedaround 1910 at Royan,near Bordeaux in France.Here, Mr. Bochaux-Praceique supplied hishouse with 1 kW of lightand power from a turbine,driven by air which waspumped by the oscillationsof the sea water in avertical bore hole in acliff.

Figur frå Palme?

Drawing from 1920 showing Mr. Bochaux-Praceique’s device. Reprinted with permission ofPower Magazine, The McGraw Hill Companies

J.F.&J.H.

• At about the time of the first world warpetroleum became the modern source ofenergy and conquered the world market.The interest for most other energy resourcesfaded away. A new growing interest forinstance at wave energy was initiated withthe petroleum crisis in 1973.

J.F.&J.H.

Oscillating water column (OWC)

• Sea water enters a hollowstructure with its loweropening submerged. Due towave action the inside“water column” willoscillate. With the shownproposal some water at theupper part of the “column”is drained into an elevatedwater reservoir.

From British patent No. 741494 on oscillatingwater columns.

J.F.&J.H.

• 80 m long vessel Kaimei (= sea light) fortesting various types of wave-activatedair turbines.

Copyright: JAMSTEC, JapanJ.F.&J.H.

The Salter duck

• In 1974 Stephen Salterpublished a paper on a devicewhich has become known asthe “Salter duck”, the“Edinburgh duck” or simplythe “Duck”, because thedevice, in its pitchingoscillation, resembles anodding duck. Several ducksshare a common spine. Therelative pitch motion betweeneach duck and the spine isutilised for pumpinghydraulic fluid through amotor.

spine

duckMooring

line

J.F.&J.H.

6

• During the late 1970s substantial wave-energy development programmes werelaunched by governments in severalcountries, in particular in the UK, Norwayand Sweden. The financial support wasdramatically reduced during the early 1980swhen the petroleum price became lower andwhen there in the public opinion was adecreasing concern about energy andenvironment problems.

J.F.&J.H.

J.F.&J.H.

Conversion of wave energy

• The patent literature contains severalhundreds of different proposals for theutilisation of ocean-wave energy. Theymay be classified in various ways intogroups of, a dozen or less, different types.

• To make use of the force thewaves give, we need somekind of force reaction. Theshown heaving buoy reactsagainst a fixed anchor on thesea bed. A pump, which isshown schematically, isactivated by the heavemotion of the buoy.Thepumped fluid is used to runa motor (e.g. a turbine) notshown. The turbine, in turn,runs an electric generator.

Force reaction

pump

deadweight

buoy

anchor

J.F.&J.H.

Force reaction by another body

• An alternative is to letthe wave force on thefloat react againstanother body, such asthe shown submergedbody. The power take-off pump is activated bythe relative motionbetween the two bodies.A mooring line isrequired to prevent thesystem from driftingaway from position.

J.F.&J.H.

pump

buoy

Mooringline Submerged body

or plate forforce reaction.

Steps of wave-energy conversion

Primary energy conversion forinstance to energy in pressurisedair or water or hydraulic oil.

Secondary energy conversion byturbine or hydraulic motor.Mechanical energy by rotatingshaft.

Input wave energy to awave power device

Electrical energy

Primary, secondaryand tertiary energy

conversion

Tertiary energy conversion byelectric generator.

J.F.&J.H.

Power take-off alternativesWave energy

Air flow Water flowRelative motion between bodies

Hydraulicpumps

Mechanicaltransmission

Airturbine

Waterturbine

Mechanicalgear

Hydraulicmotors

Electrical generator or direct use

J.F.&J.H.

7

Input energy from waves

Energy in working fluid (air, water or hydraulic oil)

Electrical energy

Primary energy conversionPrimary energy conversion

Turbine/motorTurbine/motor

Electrical generatorElectrical generator

Mechanical energy in rotating shaft

Loss

Loss

Loss

Schematic principle for extracting wave energy

ØTS+J.F.&J.H.

• Absorption of wave energy from the sea may beconsidered as a phenomenon of wave interference.Then wave energy absorption may be described byan apparently paradoxical statement:

• To absorb a wave means to generate a wave

• or, in other words:

• To destroy a wave is to create a wave.

J.F.&J.H.

A paradox?

Incident wave + reflected wave = standing wave

• Incident wave

• Wave reflected fromfixed wall

• Interference result:Standing wave composedof incident wave andreflected wave

=

+

J.F.&J.H.

=

+

• Incident wave

• Wave reflected from fixed wall• Wave generation on otherwise

calm water (due to walloscillation)

• The incident wave is absorbedby moving wall because thereflected wave is cancelled bythe generated wave.

“To absorb a wave means to generate a wave”- or “to destroy a wave means to create a wave”.

J.F.&J.H.

Classification of WECs

• All the different proposals andprinciples for wave energyconversion can be classified inseveral ways. We use these in orderto see the differences andsimilarities between the waveenergy converters (WECs).

J.F.&J.H.

- According to size and orientation

• Pointabsorbers

• Attenuator • Termi-nator

Wave front

Wavedirection

J.F.&J.H.

8

- According to location• � Shore-based• � Near-shore bottom-

standing• � Floating; near-shore or

offshore• � Bottom-standing or

submerged on not toodeep water.

� �

��

�

• � Submerged not far from awater surface

• � Hybrid; units of types 2-5combined with an energystorage (such as a pressuretank or water reservoir) andconversion machinery onland.

J.F.&J.H.

- According to end use of energy

• Electricity• Desalination of sea water• Refrigeration plants• Pumping of clean sea water (fish farms,

cleaning of contaminated lagoons and othersea areas with insufficient water circulation)

• Heating of sea water (e.g. for fish farms, andswimming pools)

• Propulsion of vessels• Combination with desired reduction of wave

activityJ.F.&J.H.

- According to form of primary energyconversion

•To hydraulic energy•To pneumatic energy•To mechanical energy (typical for the 19thcentury proposals)

•Directly to electricity (unfortunately noenergy-storing buffer between wave inputand electric output)

J.F.&J.H.

• The tapered channel is ahorizontal channel which iswide towards the sea where thewaves enter and graduallynarrows in a reservoir at theother side. As the waves passthrough the channel, water islifted over the channel wall andinto the reservoir due to theshortage of space which occursas the channel gets narrower.

The tapered channel

8sea

reservoir

Principle:

J.F.&J.H.

•A tapered channeldemonstration plant was builtin 1985 at Toftestallen on thewest coast of Norway. Due tothe tapering of the horizontalchannel, water is lifted to thereservoir 3 m above. Thewater in the reservoir flowsback into the sea (behind thereservoir dam and turbinehouse) through aconventional low-pressurewater turbine running a 350kW generator connected to thelocal grid.

J.F.&J.H. Copyright: NORWAVE AS, Norway, 1986

NORWAVE’s TAPCHAN • Even on a rather calmday, the effect ofsqueezing the water inthe narrowing space ofthe channel results init gaining speed andfury, giving animpressing view as thewater overtops thewalls and bursts intothe reservoir atToftestallen.

Copyright: NORWAVE AS, Norway, 1986

J.F.&J.H.

9

INDONOR’s planned TapChan power plant in Indonesia

Installed power: 1,1 MWReservoir level: 4 mReservoir surface: 7000 m2

Collector: Length: 126 m. Max. width: 124 mTapered channel: Length: 60 m. Max. width: 7m. Bottom: -8 m

Oscillating water column (OWC)

Principle:• In an oscillating water column

a part of the ocean surface istrapped inside a chamberwhich is open to the sea belowthe water line. When theinternal water surface movesup and down in response toincident waves outside thechamber, the air in thechamber is pressed and suckedthrough a turbine due to thegenerated overpressure andunderpressure.

air

fixed platform

Turbine and generator

Waves

J.F.&J.H.

The Wells turbine

• For a Wellsturbine thedirection of thetorque isindependent of thedirection of the airflow. This issuitable for theair’s oscillatingmotion induced bythe sea waves.J.F.

&J.H.

Copyright: JAMSTEC, Japan

Sanze shoreline gully• A lot of different designsof the OWC have beenrealised for research anddemonstration purposes.The picture shows aJapanese OWC which wastested at Sanze on thewest coast of Japan in1984. It had two Wellsturbines on each side of a40 kW generator in orderto cancel the thrust forceson the rotating shaft. Copyright: JAMSTEC, Japan

J.F.&J.H.

Kværner Brug’sOWC plant at

Toftestallen , Norway

• The OWC structure isconcrete below level +3,5m and a steel structurebetween +3,5 m and +21m. The machinery has avertical shaft The generatorhousing is at the top.Below is the (red) housingfor the self-rectifying airturbine (500 kW).

Photo: J. Falnes, 1985.J.F.&J.H.

ShorelineOWC,Isle ofIslay,

Scotland• This device was• erected by• Queens• University,• Belfast,• in a project• sponsored by the Department of Trade and Industry. The plant has a

75 kW Wells turbine and flywheels for energy storage. The systemhas been connected to the island’s grid since 1991, but is now (1999)under decommisioning, as a new, improved design, LIMPET, is underconstruction just north of the previous site (next slide).

Photo: Håvard Eidsmoen, 1993

J.F.&J.H.

10

LIMPET

• The new OWC at Isle of Islay, LIMPET,with a 500 kW electric generator.

Acousticbafflearoundair outlet/inlet

Wells turbine +generatorassembly

Concretecollector

Incomingwave

Rockgully

OscillatingWater Column

Source: WAVEGEN, UK, 1999J.F.&J.H.

LIMPET

• Left: The old IslayOWC is seen in thebackground (right).The new LIMPETdevice is indicatedon the left.

• Right: The 500kW turbine to beinstalled with thenew OWC.

Source: WAVEGEN, UK

Source: WAVEGEN, UK

J.F.&J.H.

The PicoPower Plant,

Azores

• An OWC pilot plant• is now (1999) being• tested on the island• of Pico, Azores.• The project is• sponsored by the European Commission (JOULE programme) and

coordinated by Instituto Superior Técnico in Portugal. It has abottom-standing concrete structure and a water plane area of 144 m2.The installed turbine has a rated power of 400 kW. Apart from beinga test plant, the device is supposed to provide 8-9 % of the annualelectrical energy demand of the 15 thousand islanders.

Photo: A. Sarmento, IST, Portugal, 1999

J.F.&J.H.

Air duct with turbine and air valvefor the Pico wave power plant

J.F.&J.H.

Photo: A. Sarmento, IST, Portugal, 1999

TheMIGHTYWHALE

• A full-scale designof a device calledthe “MightyWhale” has beenconstructed inJapan, and now(1999) sea trialsare carried out inGokasho bay. Copyright: JAMSTEC, Japan

J.F.&J.H.

Backward bent duct buoy

• This buoy shape wasproposed by the Japaneseinventor and scientistYoshio Masuda. Thewaves cause the hull tomove, thereby giving riseto a change of the waterlevel in the chamber.Results from wave tanktests have been verypromising.

buoy

air

8

Principle:

mooring

J.F.&J.H.

air turbine

wave direction

11

Array of point absorbers

Source: SINTEF, Norway, 1982.J.F.&J.H.

The Trondheimpoint absorber

Source: K. Budal, 1981 Photo: J. Falnes, 1983J.F.&J.H.

KN’s device

• A proposal by KimNielsen in Denmarkconsists of a heaving buoyconnected to a bottom-standing concrete base.The motion of the buoyresults in a pumping thatlowers the pressure in andremoves water from thebase housing. Then waterfrom outside can drive thelow-pressure turbinewhich generateselectricity.J.F.

&J.H.

pump

buoy

8 water out

water inthroughturbine

base

rectifying valves

TheRAMBØLL

point absorber

• The Rambøll point absorberrepresents a continuation of thework with the KN device inDenmark. A difference is thatthe power take-off is in thefloating buoy in stead of ahousing on the sea bed Photos: RAMBØLL, Denmark, 1998J.F.

&J.H.

Photo: Technocean, Gothenburg, Sweden, 1984

The Swedish hose pump

• This Swedish heaving buoyhas uses a specially designedhose to pump sea water tohigh pressure.

J.F.&J.H.

Float

Hosepump

Reaction Plate

Compressed Sea Water to Generator

Sea bed

Source: Tom Thorpe, UK

J.F.&J.H.

Three hosepump units placed in the sea at Vinga, offthe Swedish west coast.

Photo: Technocean, Gothenburg, Sweden, 1984

12

The Swedish IPS buoy

Photo: Technocean, Gothenburg, Sweden, 1981

The wave-power IPSbuoy slides up anddown along a verticalrod connected toinertial mass somedistance down in thewater. By mechanicalor hydraulic means,activated through therelative motionbetween the buoy andthe rod, wave energyis converted to usefulenergy.

J.F.&J.H.

Chinese navigationlight buoy

• In China, research hasbeen carried out at morethan ten universitiessince 1980. The pictureshows a 60W Chinesenavigation light buoy,deployed in 1985 byGuangzhou Institute ofEnergy Conversion.

Photo: Niandong Jiang, China, 1987J.F.&J.H.

TheConWEC

device

• ConWEC is an OWC devicewhere the more usual airturbine is replaced by a floatwith hydraulic power take-off.

J.F.&J.H.

Photo and figure: ConWEC, Norway, 1998

wavedirection

t

Optimal phase at resonance

Phase control by latching

Pitching raft• A system called the McCabe Wave Pump has been designed to

produce drinking water or electricity by use of wave energy. It hasbeen developed by Dr. Peter McCabe and a team of engineers fromHydam Technologies Limited in Ireland. The device makes use ofthe slope change on the water surface due to waves. A 40 m longprototype was launched in the Shannon River near Kilbaha, CountyClare in Ireland in 1996.

Equipment Cabin

Bow Pontoon Aft Pontoon

Hydraulic Pumps

Central PontoonSteel TubesDamper Plate

Hinge

J.F.&J.H.

Source: Tom Thorpe, UK

Animation of “Pelamis”

pursued by the Scotch companyOCEAN POWER DELIVERY LTD.

http://www.oceanpd.com

13

The Pendulor

• A new design of a devicecalled Pendulor is being tested(picture) in the sea nearMuroran, Hokkaido, Japan.

Photo: Tomiji Watabe, 1999

J.F.&J.H.

Source: Tomiji Watabe

The SEA Clam• As a part of the UK

Wave EnergyProgramme, researchand development havebeen carried out byCoventry Polytechnicin England. The resultis a flexible bag devicecalled the SEA Clam.A circular design wastested at 1/15th scale inthe Scottish lake LochNess in 1986.

Principle:

8airflexible bag

spine

mooring

J.F.&J.H.

wave direction

• Model with 12 airchambers, (black)rubber membranesand instrumentationcables prepared fortest.

• Below: Model withwhite rubbermembranes under testin Loch Ness.

Test of 1:15 scaleCLAM model in Loch

Ness

Test of 1:15 scaleCLAM model in Loch

Ness

Photos reproduced by permission of L.Duckers/Sea Energy Associates, UK

J.F.&J.H.

The Bristol cylinder• This wave energy device was

proposed by David Evans at theUniversity of Bristol in England. Inresponse to an incident wave thesubmerged horizontal cylinderoscillates vertically and horizontally.With a sinusoidal wave the combinedoscillation results simply in a circularmotion whereby all the incident waveenergy may be absorbed provided thehydraulic power take-off is able toprovide for optimum amplitude andoptimum phase of the circular motion.The hydraulic power take-off is builtinto the anchors.

Principle:

cylinder

anchors

Hydraulicpump

J.F.&J.H.

wave direction

Wave-drivensea-water pump

• In this OWCthe airchamber ispartlyevacuated.Thus seawater ispumpedacross a sandbarrier. Sand barrier

Coastallagoon

Ocean

Source: S.P.R. Czitrom,Mexico, 1995

J.F.&J.H.

Is wave energy commercial?

• Wave energy utilisation is still in an earlystage of technological development. It iscommercially competitive in certain markets,such as to supply power for navigation buoys,for water desalination plants, and for isolatedcoastal communities with expensive electricityfrom diesel aggregates. With further researchand development wave-energy devices willbecome economically competitive in anincreasingly larger part of the energy market.

J.F.&J.H.

14

Cost reduction by experience and learning

• It is a well-known fact that due to experience andimproved methods of production the unit cost of aproduct usually diminishes as the production volumeis increased. Thus, for electricity production in theUS during 1926 to 1970 there was a main trend of25 % decline in the inflation-corrected price for eachdoubling of the cumulative production. For retailgasoline processing the corresponding decline was20 %. (J.C. Fischer, Energy Crisis in Perspective,John Wiley, New York, 1974.)J.F.

&J.H.

Estimated cost of electricity from variousOWC devices versus year of design.

0

5

10

15

20

1980 1985 1990 1995 2000

Design Year

Early Nearshore OWCWavegen OSPREYShoreline OWC

Source: Tom Thorpe, UK, 1998

J.F.&J.H.

Cos

t of E

lect

ricity

(pen

ce/k

Wh)

Estimated cost of electricity from various offshorewave-energy devices versus year of design.

1

10

100

1980 1985 1990 1995 2000

Year of Design

Cos

t of E

lect

ricity

(pen

ce/k

Wh)

Edinburgh DuckBristol CylinderSEA ClamPS FrogMcCabe Wave PumpSloped IPS Buoy

Source: Tom Thorpe, UK, 1998

J.F.&J.H.

Experience curve example: Estimated investmentcost (c) relative to installed power capacity (P)versus cumulative volume of total installed capacityof wave power plants.

c (EU

R / W

)

Source: J. Falnes, 1995

J.F.&J.H.

Promoting new energytechnologies

• During the initial stages of the developmentof a new energy technology niche marketswill be helpful. Otherwise, governmentalsubsidies to cover the difference betweencost and market price may promote a newtechnology.

J.F.&J.H.

Initial handicap for newenergy technologies

• Experience curves illustrate the handicapwhich new energy technologies haveinitially, in market competition with well-established conventional energytechnologies. This fact must be borne inmind when comparisons are made of energycost from new and conventionaltechnologies. Such comparisons would belike comparing the performance of a childwith the performance of an adult.

J.F.&J.H.