6.3 Wave and tidal power generation - treccani.it Waves are formed by wind blowing across the...

6.3.1 Introduction

The seas and oceans of the world are a vast store ofenergy. Ocean energy is manifested in many forms andof these, the best known and most freely available, arewave and tidal energies. No one really knows howmuch power can practically be extracted from theoceans but in the UK, the Marine Foresight Panel,reporting to the Government, stated that, “It has beenestimated that if less than 0.1% of the renewableenergy available within the oceans could be convertedto electricity it would satisfy the present world demandfor energy more than 5 times over” (UK Office ofScience and Technology, 1999). Clearly, this is a vastresource and both governments and private industryare making increasing efforts to develop the

technologies needed for its exploitation. With minorexceptions, the means of extracting power from waveand tide are quite distinct; this reflects the widelydifferent characteristics of the two energy sources.

Wave energy occurs due to the movement of waternear the surface of the sea. Waves are formed by windblowing across the surface of the water to promotewave generation and growth. Since the winds derivefrom the action of the Sun on the atmosphere, wavesrepresent a store of solar energy. In deep water,individual water particles make circular motions whilstenergy is transmitted in the direction of wavepropagation. In the absence of a current, there is nonet movement of the water as the energy moves; this isin sharp contrast to tidal power where both energy andwater move together.

575VOLUME III / NEW DEVELOPMENTS: ENERGY, TRANSPORT, SUSTAINABILITY

6.3

Wave and tidal power generation

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Tidal energy is available as a consequence of themovement of the huge quantities of water in the seasand oceans associated with the tides. The tides deriveprimarily from the gravitational attraction of the Moonon the water mass, coupled with the rotation of theEarth around the Sun, and power lost in tidalmovement results in an infinitesimal reduction in thedistance between the Earth and the Moon and in aslowing down of the Earth. Thus the Earth and itsnearest neighbour in space lose both potential andkinetic energy to fuel the tides. As the tides ebb andflow, the water height near a coast changes, offeringthe opportunity to extract power from the changes inpotential energy associated with the height difference.Also, as a consequence of the shape of coastlines and

general bathymetry, tidal flows are not uniformthroughout the world and in some areas the flows areconcentrated into strong tidal streams. These streamscontain large quantities of kinetic energy which is alsoavailable for capture and conversion.

Whilst some might disagree, it is probably fair tostate that at the time of writing, there are no whollycommercial wave or tidal generation schemes. Thereare tidal schemes, such as those at La Rance, nearSt. Malo in France, and at Annapolis in the Bay ofFundy in Canada, which make a significantcontribution to the local electricity supply, and theLimpet wave energy plant on the Scottish Island ofIslay, which has been feeding the local grid since itscommissioning in 2000.

We are now entering an era in which it is believedthat wave and tidal generation can make a major, andcost effective, contribution to power generation incoastal states. The first decade of the Twentiethcentury has seen an explosion of interest in thetechnology for power extraction and a plethora ofprototype devices are due for installation andcommissioning.

There is more energy in the sea than man is everlikely to use but unfortunately only a very smallproportion of this will be accessible using thetechnologies currently under development. Waveenergy is measured in terms of the power in each metreof wave front and is typically given in units of kW/m.An indication of the available wave power in differentdeep water locations worldwide is given in Fig. 1.

576 ENCYCLOPAEDIA OF HYDROCARBONS

POWER GENERATION FROM RENEWABLE RESOURCES

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possible tidalbarrage sites

approximately resourcein GW at reasonable cost

mean tidal rangeappropriate toinstalled

Fig. 3. Areas suitable for tide barrages.

Waves generated in deep water lose very little oftheir power until they start to ‘feel the bottom’ andpower is lost to bottom friction. This typicallybecomes significant when the water depth fallsbelow half a wavelength. An example of the fall inavailable power with water depth is shown in Fig. 2.The rate of fall of power with depth depends uponthe local bathymetry and particularly on the slope ofthe seabed. A long shallow slope will dissipate morepower than a short steep rise. The higher power indeeper water makes deep water attractive to manytechnology developers but the environment indeeper waters is also more severe than inshore andas such the technical aspects are potentially morechallenging.

Tidal power resource varies with the square oftidal range. Fig. 3 shows areas that have beenidentified as suitable for tidal barrage schemes.These aggregate to 239 GW. Whilst this diagramhighlights the optimal sites worldwide, it is by nomeans exhaustive and represents only a smallproportion of the power in the tides. Tidal streamdevices need a strong current rather than a largetidal range and a mean spring peak velocity of 2.5 m/s is typically quoted as necessary foreffective generation.

Generic wave energy technologiesThere is no unique means of classifying wave

energy extraction systems. The classification chosenhere is arbitrary and not all encompassing, but itnonetheless describes the majority of wave energydevices currently under development. The selectedcategories are: a) overtopping devices; b) articulatedrafts; c) Oscillating Water Columns (OWC); d ) floats and buoys; e) contained buoyancy; f ) subseaturbine.

A list including existing or proposed examples ofwave energy devices in the various categories isgiven in Table 1.

Overtopping devices. These rely on wave actionto drive lift water up a ramp from where it spillsinto a reservoir. In some devices, a flat ramp ofconstant width is used and under typical operatingconditions the water may be lifted 3 m. Water fromthe reservoir discharges back to the sea through aturbine (typically a Kaplan form) usingconventional low head hydrotechnology adapted forthe marine environment. The first majordevelopment of this form was the Tapchan unit(Tapered Channel) designed for use on the coastutilizing a land-based reservoir. The technology hassubsequently been adapted by a number ofdevelopers for deep-sea use employing a floatingreservoir and ramp.

Articulated rafts. These rely on the relativemotion of segments of the raft to allow powerextraction. The ability of one raft segment to workagainst its neighbour gives a self-referencing systemand avoids the problem of having to tie the workingpart of the device rigidly to the sea bed to give theunit something to work against. A hydraulic pump istypically fitted between each pair of raft segments.The pump supplies an accumulator from whencepressurized fluid drives a motor and generator. Raftstypically lie perpendicular to the incoming wavefront and the wave is attenuated as it passes downthe raft. For this reason articulated rafts aresometimes grouped with other device types whichlie at right angles to the waves and are calledattenuators. This is in contrast to devices that lieparallel to the wave front, providing a completeobstruction to the passage of waves. These are calledterminator devices.

Oscillating water columns. These are one of themost popular wave energy device types. An OWC comprises a partly submerged structure(or collector) which has an opening to the seabeneath the water surface. Under wave action,water flows in and out of the opening. This, in turn,alternately compresses and rarefies the air withinthe collector above the water surface. The air,driven by piston action passes through a turbineunit which extracts power and drives a generator.The most commonly used turbine is theself-rectifying Wells turbine which, whilst having a peak efficiency lower than some other designs,scores in terms of simplicity and whole cycleperformance. Prototype OWC units have beenoperational in various parts of the world since themid 1980s and developers have more fieldexperience of this technology than any other.

Floats and buoys. These have been used aspower collectors in many wave energy systems. Ithas been shown mathematically and practically thatrelatively small buoys can draw in power from awave front larger than the diameter of the buoyitself and this ‘point absorber’ effect providesmuch of the attraction of buoy designs. Somesystems use a rigid buoy and employ its buoyancyto drive a power take-off mechanism. This may bein the form of a hydraulic cylinder between thebuoy and the seabed, or between the buoy and adamper plate, or it may be an inertial referencesuch as a water mass. In one particular design, anelastomeric hose is used as a pump instead of amore conventional hydraulic cylinder. Some buoyscontain a water column and, using the relativemotion between the buoy and the water surface todrive the water column, extract power through the


WAVE AND TIDAL POWER GENERATION



Table 1. Wave energy devices in development (March 2005)

Generic type Device nameCompany/

organizationLocation Status Country

Overjopping device

Wavedragon Wave Dragon ApS Floating Prototype Denmark

Seawave Slot-coneGenerator (SSG)

WAVEenergy Fixed Concept Norway

WavePlaneWaveplaneProduction

Floating Small scale prototype Denmark

FWPV SeaPower Floating Prototype Sweden

Articulated raft

WavebergWaveberg

DevelopmentMoored, floating Prototype United States

McCabe Wave Pump Hydam TechnologyMoored, floating

with reaction platePrototype Ireland

Pelamis Ocean Power Delivery Moored, floatingGrid connected

prototypeUK

Oscillating WaterColumns (OWC)

LIMPET Wavegen ShorelineGrid connected

prototype UK

LIMPET ST Wavegen Breakwater applicationsGrid connected

prototype UK

EnergetechNearshore, bottom

standingPrototype Australia

Guangzhou Institute of Energy Conversion

Shoreline Ongoing project China

JApanese Marine Scienceand TEchnology Centre

(JAMSTEC)Floating OWC Prototype Japan

National Institute of Ocean Technology

Nearshore,bottom standing

Prototype India

Grampus Ocean Wave Energy Floating OWC Concept UK

Pneumatically StabilizedPlatform (PSP)

Float Large raft

incorporating OWCsystems

Concept United States

Sperboy Embley EnergyMoored buoy,

multiresonant OWCGrid connected

prototype UK

MRC100 OREConMoored buoy,

multiresonant OWCGrid connected

prototypeUK

Float/buoy

WaveMill Wavemill Energy

CorporationNearshore bottom

standing reference frameSmall scale prototype United States

AquaBuoy AquaEnergy GroupMoored buoy.

Inertial referenceSmall scale prototype United States

WaveBob ClearPower TechnologyMoored buoy,reaction plate

Small scale prototype UK

SDE Energy Restrained plate Small scale prototype Israel

Wave Rider SeaVolt

TechnologiesMoored, floating Tank tests United States

Scientific Applicationsand Research Associates

(SARA)Bottom standing Laboratory prototype United States

Salter Duck University of Edinburgh Model tested UK

Containedbuoyancy

ArchimedesWave Swing

AWS Ocean Energy Bottom standingGrid connected

prototype UK

SeaDog PumpIndependent Natural

ResourcesBottom standing Tank tests United States

Wave Master Ocean WaveMaster Bottom standingTank tests

on 20 m long unit UK

Power Buoy Ocean PowerTechnologies

Moored buoy Prototype United States

Subsea turbine WaveRotor Ecofys UK Bottom standing Model tests UK

turbo-generation mechanism described above. InTable 1 these OWC buoys have been included inthe OWC section. A significant difficulty in thedesign of a wave energy buoy is the provision of,and adequate reaction to, the forces driving thewave energy collector, without transmitting thisforce to the foundation or mooring.

Contained buoyancy. In a surface-piercing buoythe change in water height on the buoy exteriorcauses a change in buoyancy that provides a drivingforce to the system. If a rigid buoy is fullysubmerged then the passage of a wave does notaffect the buoyancy and there is no driving forcefrom this source. If, however, the buoy is flexible,then the pressure change caused by the passage of awave will cause the buoy to change in volume with asubsequent change in buoyancy. This principle isused in a number of wave energy devices in which avolume of air is trapped but exposed to the local seapressure. Typically, there will be an air-filled buoythat is open at the base and the air is pressurized sothat the buoy will be neutrally buoyant at aprescribed distance beneath the surface. As a wavecrest passes, the pressure on the air will increase,buoyancy is lost due to air compression and the buoysinks. A limit on the buoy displacement prevents arunaway situation. As a wave trough passes, thereverse happens and the buoy is driven upwards.Power take-off is via hydraulics or a linear generator.Similar systems have been proposed using sea floormounted pressure pads.

Subsea turbine. This system uses aself-rectifying turbine directly in the water, therebyeliminating the need to convert the hydraulic powerin the sea into pneumatic power before extraction.

Generic tidal energy systemsTidal power systems fall into two main groups,

tidal barrage or tidal stream. The operation of atidal barrage involves the construction of a barrier toobstruct a natural tidal flow. The flow restrictioncreates a height difference on either side of thebarrier and this pressure head is used to drive a lowhead hydroelectric system. Tidal stream devices relyon extracting the kinetic energy directly. There arethree generic classes of tidal stream device.

Tidal stream turbines. These work on a similarprinciple to wind turbines and indeed may look quitesimilar. Both horizontal and vertical-axis machinesare being investigated, some with ducting/cowlingaround the rotor. The turbine may be coupleddirectly to a standard generator via a gearbox, or usean alternative power train design.

Reciprocating tidal stream devices. These havehydrofoils that move back and forth in a plane

normal to the tidal stream, instead of rotating blades.One design uses hydraulic pistons to feed ahydraulic circuit, which turns a hydraulic motor andgenerator to produce power.

Venturi effect tidal stream devices. In these, thetidal flow is directed through a duct whichconcentrates the flow and produces a pressuredifference. This causes a secondary fluid flowthrough a turbine.

In addition to the main groupings there areother novel approaches to the extraction of tidalpower, such as the direct extraction of power fromthe flow using magneto-hydrodynamics and theapplication of an unstable articulated raft. Asummary of tidal stream systems underdevelopment is given in Table 2.

6.3.2 Historical perspective

The earliest recorded application of tidal power wasto drive a tide mill in the Fifteenth century. Theearliest use of wave power is believed to have beenin navigation aids. Wave-driven whistling buoyswere in common use towards the end of theNineteenth century where air, trapped in the canopyof a floating buoy, was expelled through a whistle towarn mariners of local peril at night time or in caseof a coastal mist. Whistling buoys were theforerunners of all modern OWC wave energysystems. Prior to the introduction of a whistle, bellbuoys were in common use, where the rocking of abuoy under wave action caused a bell to ring.Unfortunately, fog and calm waters tend to coincideso that bell buoys were least effective when mostneeded. To overcome this problem some bells, suchas those at Whitehead in Maine, United States, in1830, were placed on the shoreline and operatedmanually. In 1837, equipment was fitted to drivethe bell using the tides and, save for tide mills, thisrepresents the earliest recorded application of tidalpower. It was over half a century before the nextsignificant development in wave power. Again, thisoccurred in the field of navigation buoys when in1947, Masuda in Japan designed and installed thefirst OWC, driving an impulse turbine to produceelectricity. The unit was sited in Osaka Bay and theelectricity which was generated supplied power tonavigation lights. Security of operation wasprovided by rechargeable batteries which took theirpower from the turbine/generator in times of plenty.A commercial range of buoys was developed fromthis original and are still available from theRyokuseisha company in Japan. Whilst the outputof each unit is small (70-500 W), this still



represents the most common application of a waveenergy plant.

After the initial development of the navigationlight buoy there was little interest in the furtherdevelopment of wave energy until 1973. Then, thesharp rises in oil prices, resulting from theMiddle Eastern conflict that year, caused thegovernments of the developed nations to examinetheir energy dependence on fuels imported frompolitically sensitive areas and to consider

alternative, more secure options. Wave energydevelopment programmes were initiated in anumber of countries, most significantly in theUK, where from 1974 to 1983 a total of £15m ofgovernment money was spent. The basic objectiveof the UK programme was, “To establish thefeasibility of extracting energy from ocean wavesand to estimate the cost of this energy if used on alarge scale to supply UK needs” (Davies et al.,1985).



Table 2. Tidal stream device developers (March 2005)

Generic type Device nameCompany/

organization Location Device Status Country

Tidal current

Stingray Engineering Business Bottom standingReciprocating

hydrofoilPrototype UK

Tidal HydraulicGenerators

Bottom standing Horizontal turbine Prototype UK

TidElSoil Machine

DynamicsBuoyant against

mooringHorizontal turbine Tank model tests UK

Underwater ElectricKite

UEK SystemsBuoyant against

mooringHorizontal turbine Field model tests United States

StatkraftBuoyant against

mooringHorizontal turbine Research project Norway

Verdant PowerMounted from

floating platformHorizontal turbine Field model tests United States

Tidal FenceBlue Energy

Canada

Buoyant againstmooring or fixed

in breakwaterVertical axis turbine

Small scale fieldtrials United States

Gorlov HelicalTurbine

No mountingspecified

Spiral vertical axisturbine

Turbine prototypetested United States

Open Centre Turbine Florida HydroNo mounting

specified Open centre turbine

Turbine prototypetested United States

Blue Concept Hammerfest Strøm Bottom standing Horizontal turbineGrid connected

prototype Norway

Rochester VenturiImperial College

InnovationsMultioptionmounting

Venturi air turbine Prototype UK

HydroHelixHydroHelix

EnergiesBottom standing Horizontal turbine Test model France

Inocean AS Mechanical Eel Floating unitArticulated

submerged raftConcept Norway

VariousKinetic Energy

SystemsBottom standing Horizontal turbine Concept United States

Rotech Tidal Turbine Lunar Energy Bottom standing Ducted horizontal

turbineTest model.

Prototype planned UK

SeaFlowMarine Current

Turbines

Bottom standing,surface piercing

towerHorizontal turbine

Prototype. 2nd

Prototype underconstruction

UK

Mermade Mermade Energy Conceptual Variable orientation

turbineConcept UK

Magnetahydrodynamicconversion

Neptune Systems Conceptual MHD (Magneto-

HydroDynamics) withsuper conductors

Concept Netherlands

Tidal lagoon Tidal Electric Project proposals UK

A range of technologies was considered, basedupon the requirement for a 2 GW scheme, but in1982 it was concluded that, “The overall economicprospects for wave energy looked poor whencompared with other electricity-producingrenewable energy technologies” (Davies et al.,1985). Notwithstanding the widespread criticismof this conclusion from within the wave energycommunity, the programme was halted with theexception of the continuing small-scaledevelopment of the more promising systems. Theongoing programme led to Queen’s University,Belfast, building a 75 kW demonstration shorelineOWC on the Scottish Island of Islay (Whittaker et al., 1997). The plant first ran in 1991 andcontinued in intermittent operation until it wasdecommissioned in 2000. The grid-connected plantused a Wells turbine/induction generatorcombination to convert the pneumatic power fromthe OWC to electricity and the researchprogramme provided field data (Whittaker andStewart, 1994) to aid the design of subsequentplants; most notably Wavegen’s LIMPET OWC,also on Islay (Heath et al., 2000; Folley et al.,2002). The Wavegen LIMPET has beengrid-connected and operating since 2000.

Between 1976 and 1979, a Japanese teamoperating under the auspices of the InternationalEnergy Agency tested OWC units mounted on afloating barge, the Kaimei. The 800 t, 80 m longbarge was moored off the coast of Yura, Tsuruokacity, Yamagata prefecture (Fig. 4). With Japan as the lead national partner there were contributionsfrom the UK, Canada, Ireland and the US. EightOWC chambers were mounted in the barge, eachwith a nominal 125 kW rating. A range of powertake-off units were tested including theself-rectifying Wells and McCormick turbines andmore conventional turbine systems usingrectification valves.

A number of demonstration OWC plants havebeen constructed, either in the shoreline or inbreakwaters, elsewhere in Japan. The Sakata portOWC is the largest of those built and tested inJapan during the 1980s and 1990s. The device isa five-chambered OWC built as part of a harbourwall. It is a concrete caisson structure that wasfloated into position before being sunk and filledwith ballast. The machine, which becameoperational in 1989, is fitted with a tandem Wellsturbine. The original rating of the machine was60 kW.

A second floating OWC system, the MightyWhale, was launched in 1998 for sea trials. Theprototype, developed by the Japanese Marine

Science and Technology Centre (JAMSTEC), is 50 m long, 30 m wide and 12 m deep and designedto float at a draught of 8 m when ballasted. Thestructure contains three OWC units each of whichdrives a Wells turbine. The total system rating is 110 kW. This low output for the device size is areflection of the relatively low incident wave powersavailable in Japan, in comparison to the moreenergetic seas incident on Western Europe andelsewhere.

A parallel programme, but on a smaller scalethan in the UK, was performed in Norway wherework initially concentrated on a point absorber buoyreacting against its mooring and on the use ofsubmerged plates to focus wave energy to thecollector. Attention then moved to examine thepotential of the OWC, and with the support of theindustrial company Kvaerner Brug, a 500 kWcliff-mounted unit was built in 1985 near Bergen.This unit was destroyed during storms in 1988. Ithas been reported that the failure was a consequenceof corrosion fatigue in the bolts holding the deviceto the cliff.

A cellular concrete collector was built by a teambased at the Ocean Engineering Centre of the IndianInstitute of Technology in Madras. The projectstarted in 1983 and came to fruition in October1991, when the plant was connected to the local gridand energized. The 6,000 t device (structural weight3,000 t�3,000 t ballast) was designed to be stable inbreaking waves of up to 7 m and was placed on aprepared rubble mound. The original Wells turbinewas replaced by an impulse turbine but withoutperformance improvement.

Meanwhile, in the People’s Republic ofChina, a shoreline OWC was built on Dawanshanisland (European [...], 1994) in the South ChinaSea in 1989 and run briefly for test purposes. A Wells turbine of 0.8 m diameter was connectedto a 3 kW 1,500 rpm generator. The air chamberwas 4 m wide and 3 m deep with average seaconditions of 4.4 kW/m. The tests wereconsidered successful with chamber efficiencies



Fig. 4. Kaimei barge (courtesy of the Author).

of 50-150% reported and overall efficiencies of10-35%.

In 1986, the Tapchan device (Fig. 5) becameoperational. Tapchan, or the Norwegian TaperedChannel, comprises a collector, a converter, areservoir and a low head hydrogeneration plant. Theenergy collector is a naturally-occurring gully nearToftesfallen on the North Sea coast of Norway. Thisfunnels waves into the converter which is avertically-walled channel, 6-7 m in depth, rising to2-3 m above mean sea level. The converter narrowstowards the shore so that the height of water flowinginto the channel increases as it moves shorewardeventually spilling over into the reservoir. Thereservoir itself was made by connecting existingrock formations to create an energy store with asurface area of some 8,500 m2 and enough water tokeep the 350 kW low head hydrosystem operatingfor 30 minutes in the event of insufficient waves tocause overtopping. This innovative system has manyadvantages over other wave energy generators, butsuffers the major disadvantage of having veryspecial site requirements. In an attempt to dispel thesite-specific nature of Tapchan and to remove theinfluence of the tide, a number of developers haveadopted the overtopping principle for a floatingdevice.

The Swedish government promoted a modestwave energy programme from 1976 onwards withthe main focus of interest being a floating buoysystem which, as the buoy floats upwards underwave action, stretches an elastomeric hose anddelivers the pressurized seawater into a high-pressure reservoir. From the reservoir, the fluiddrives a Pelton wheel to generate electricity. As thebuoy falls, the hose relaxes and a fresh charge ofwater is drawn in from the sea. A number of unitswere successfully tested during the 1980s and thesystem, originally developed and tested by Inter

Project Service (IPS) in Sweden, has now beenadopted for commercial development by the United States Company Aqua Energy.

The majority of the projects described abovewere publicly funded but the combination ofreducing oil prices, the modest performance ofprototype devices and pessimistic reports on thelong-term potential of wave power resulted in adrastic diminution of governmental support for waveenergy towards the end of the 1980s. At around thistime, however, there was a growing realization thatlittle or no account was being made ofenvironmental impact in the estimation of energycosts and there was a growing awareness of theimportance of fossil fuel emissions influencingglobal warming. There was a growing belief that ifthe full environmental cost of fossil fuel and nucleargeneration were included, then fully-developed wavepower technologies would become commerciallyattractive. Fuelled by this belief, a number ofentrepreneurs entered the wave power industry andthe balance of funding changed from beingpredominantly public monies to predominantlyprivate with public support. Foremost among thesewas A. Thomson, who with A. Wells, inventor of theWells turbine, set up Wavegen in the UK to developOWC technology and in Australia, Energetech wasestablished by T. Denniss to develop a deviceoperating on similar principles. In Holland,Teamwork Technology, led by F. Gardner and H. vanBruhgel started the Archimedes Wave Swing (AWS)project and, more recently, R. Yemm set up OceanPower Delivery (OPD) in Scotland to commercializethe Pelamis articulated raft (Yemm, 2003).SeaPower, in Sweden, established work on a floatingovertopping device whilst the Wave Dragonconsortium, based in Denmark, started thedevelopment of an overtopping unit with widefocussing arms.

6.3.3 Current status

Wave energy plantsThe injection of interest from private

companies and the realization that a wide portfolioof renewable powers was necessary to meet thechallenge of global warming led to renewedinterest from governments and other public bodiestowards the end of the 1990s and this has carriedthrough into the new millennium. The form ofpublic support varies. The EU frameworkprogramme fosters international co-operation bysupporting ‘thematic networks’ and alsocontributing to specific projects, which incorporate



Fig. 5. The Tapchan device (courtesy of the Author).

wave energy (Clément et al., 2002). ThePortuguese offer preferential tariffs to wave-generated power, whilst the UK government issplitting its support between proof of conceptprojects and larger scale grid-connecteddemonstrator projects which receive capital grantsand revenue support. Other support mechanismsoperate elsewhere. Whilst welcome, the industry is,in general, still at the development stage and wouldprefer greater public support at this pre-commercial stage. Some developers arenonetheless starting to make sales. The followingprototype units are either in operation or scheduledfor deployment.

SeaPower FWPV. Having tested a reduced scaleprototype of their Floating Wave Power Vessel(FWPV; Lagstroem, 1999) the Swedish companySeaPower International AB has announced plans todeploy a 1.5 MW unit off the coast of the ShetlandIslands. The 160 t pilot plant was tested in the opensea for eight months, including a winter period, andon the strength of these trials, the company won acontract in the UK for the supply of renewablepower under the Scottish Renewables Obligation in1999.

Pelamis (OPD). The Pelamis articulated raft isundergoing trials at the European Marine Energytest Centre (EMEC) on Orkney (Thorpe, 1998,1999). It is an articulated raft made up of four 30 mlong cylindrical segments. A novel feature is that theinterconnecting joints between segments move at anangle to the vertical so that a heave action ispartially converted into sway and vice-versa. Thisoffers interesting tuning capabilities and enables anexcellent coupling to the waves in a wide range ofwave conditions. A successful series of tests atEMEC will lead to commercial orders for thesystem. The device is typically slack-moored in 50 m of water and is designed to tunnel throughlarge waves to avoid overloading either structure ormooring. The hydraulic control system allows forpower to be fed back into the sea in order to activelytune the device and maintain optimal tuning to theincoming wave field.

AWS Ocean Energy. The Archimedes WaveSwing prototype (Vriesema, 1995) was successfullydeployed in 2005 off the coast of Viana do Costellain Portugal for a series of field trials. The waterdepth at the tests site was 46 m. The containedbuoyancy device comprises a floater, containingtrapped air, which sits atop a lower cylinder and therelative movement between the two, caused by waveaction, is restrained by a set of linear generatorsgiving direct conversion of mechanical power toelectricity. The generated power is returned to the

shore via a sub sea cable. The prototype unit wasbuilt on a self-floating steel frame designed tofacilitate placement and recovery during thedevelopment phase of the project. Fig. 6 shows theunit in dock, prior to deployment, with the floatersitting on the deck. It is anticipated that productionversions of the system will not have the steel framebut will comprise units floating sub surface andslack moored to the seabed.

Energetech. The Australian company Energetechdeployed its prototype OWC collector in 2005. Thesteel structure includes a section in front of theOWC collector which focusses the incoming wavepower onto the collector entrance. This focussingenables the collector to work at higher pressuresthan otherwise and leads to more effective materialuse than with an unfocussed system. The site for theprototype installation at Port Kembla near Sydneywas chosen for its relatively benign waveenvironment; the objective was to test the generationcapacity of the device without exposing the unit toextreme weather. Further development is expectedon the structure and the mooring system, prior toinstallation in a more energetic environment. Thecollector is fitted with a novel power take-off whichuses the Dennis-Auld turbine instead of the moreconventional Wells unit. This turbine is activelycontrolled, as it depends on wave conditions toremain in an optimal operating situation. The powertake-off is through an inverter-driven inductionmachine.

Wavegen. Wavegen’s LIMPET collector has beenin service on the Scottish island of Islay since 2000and continues to supply power to the local gridwhilst at the same time serving as a test and proving



Fig. 6. AWS prior to deployment (courtesy of INETI).

facility for the next generation of turbine powertake-off units (Fig. 7). Using the experience gainedthrough plant operation, Wavegen have designed amodular power take-off unit for general applicationin any type of OWC collector. Each unit comprises apair of Wells turbines co-rotating on either end of athrough-shaft induction motor which has beenspecifically designed for the application. Thehousing of the turbo-generation unit connects to acontrol and isolation valve, and facility is providedfor the fitment of an in-line silencer. In contrast tothe majority of devices to date, the modular unitshave been designed for series production so that thewave energy industry can start to take advantage ofthe economies of scale. The initial market for thefirst in a size range starting at 20 kW is for fitmentto breakwaters. At a typical spacing of one moduleper 4 m of breakwater, a caisson breakwater can,with minimal modifications to the civil engineering,be converted to a generator with a typical rating of 5 MW/km of breakwater. Wavegen are currentlyperforming reliability trials on prototype units prior

to commercial deployment. A prototype modularassembly is shown in Fig. 8.

Tidal plantsUntil the last few years of the Twentieth

century, efforts to extract power from the tides hadcentred on tidal barrage schemes. The most notableof these was the 240 MW installation at La Rancenear St. Malo in France (Fig. 9). Construction ofthe plant was completed in 1967 after a 7-yearbuilding period. The barrage incorporates a roadcrossing over the estuary of the river Rance and isfitted with a total of 24x10 MW bulb turbines eachof 5.4 m diameter. A similar but smaller plant (20 MW) was opened in 1984 in Annapolis Royalon the Bay of Fundy in Canada. More recently,however, attention has switched to tidal streamgenerators and the more notable developments aredescribed below.

Marine Current Turbines. The prototype 300 kW SeaFlow turbine was tested off Lynmouth,feeding power into a dump load (Fig. 10).Performance was described as 27% better thanexpected and a 1 MW device is planned.

Blue Energy Canada. The technologypromoted by Blue Energy is based upon theapplication of the Davis Hydro Turbine, which is adevelopment of the vertical-axis Darreius windturbine. The long-term objective is to mount theseturbines in large numbers in a ‘tidal fence’ (Fig. 11)where the ‘fence’ structure can double as a roadcauseway, thereby sharing the cost. The companyhas tested six units of different sizes. The largestrating was 100 kW.

HydroVenturi. This company was originally aspin-off company from Imperial College,London, and now has offices in London and SanFrancisco. They use a fixed structure, containinga venturi, to accelerate the tidal flow and create adepression within the venturi that can be used toinduce flow in a secondary pipe. The secondarypipe can be shore-mounted, thereby neatly



Fig. 7. Completed LIMPET on Islay, The Hebrides (courtesy of Wavegen).

Fig. 8. Prototype of power generation unit modular assembly(courtesy of Wavegen).

removing any moving parts to a place of relativeconvenience. A prototype was tested in Grimsby.The system is inherently less efficient in terms ofextractable power per power flowing through theventuri than a turbine exposed to the full flow.However, it does have the great advantage ofrelatively easy access.

Hammerfest Strøm. This is a company set up tobuild a tidal generator for Hammerfest (whichclaims to be the world’s most northerly town) andto subsequently exploit the technology. The unitwas commissioned in late 2003 and is nowsupplying the local grid. Shareholders includeABB and Statoil.



Fig. 9. Tide barrage device at La Rance (France) (Archivio iconografico IEI).

Fig. 10. SeaFlow turbine (courtesy of Marine Current Turbines).

Fig. 11. Tidal fence (courtesy of Blue Energy).

Engineering Business. The EngineeringBusiness’s Stingray device differs from the majorityof other systems in two major respects. Firstly, thepower take-off is hydraulic. Secondly, the primarydriver is an oscillating wing rather than a turbine.The prototype unit was tested in Orkney in late 2002but development has been placed on hold forcommercial reasons (Fig. 12).

SMD HydroVision. SMD are developing a twin-rotor tidal power device named TidEl. Twin-rotordevices are common because there is no (or little)reaction torque on the foundation or mooring. Therotors are buoyant and flexibly moored. A 1:10model was tested at the New and Renewable EnergyCentre (NaREC) in Blyth, UK, and goodperformance was reported.

Verdant Power. This company is a relativelynew Virginia-based company which is testing anumber of turbine concepts in open streams withthe objective of developing a business based onlow head hydro and marine currents. Its mostimpressive trial to date is that of a conventionalturbine slung beneath a pontoon on New York’sEast River.

Inocean. The Inocean ‘mechanical eel’ isradically different from other proposed tidal devicesbut remarkably similar to later developments ofWavegen’s Hydra attenuator wave power concept. Itis a segmented raft that relies on instabilities tocause snaking and allow power to be extracted fromthe relative movement of the segments.

Underwater Electric Kite. The UnderwaterElectric Kite is a well-tested conventional tidalstream turbine. The turbine module is suspended in

the tidal stream and designs exist for up to 1 MWnominal output (Fig. 13).

6.3.4 Estimation of wave energyresource and deviceperformance

Ocean waves represent a temporary store of solarpower. Differential heating of the Earth’s surface dueto the orbital movement of the Earth relative to theSun creates patterns of heating and cooling thatcreate winds. Winds, which derive from acombination of differential atmospheric heating bythe Sun and the influence of the Earth’s rotation, acton the surface of areas of open water to start waveformation. Initially, the air exerts a tangential stresson the air-water interface to initiate wave formation.The disturbed water surface then interacts with thewinds to create varying shear stresses and pressurefluctuations which, when in phase with the existingwaves, will promote further wave development. Theeffect of the air-water interactions is firstly toincrease the wave height and then to increase thelength and period of the waves. In general terms, thegreater the distance over which winds can act on thewater to promote wave growth (the fetch) the largerthe waves and the longer the predominant waveperiod. This leads to the contrast between longwavelength ocean swell and the short period wavesproduced in a local storm. At any particular locationthe actual movement of the water surface will be acombination of many different wave systems and anaerial view will often reveal a predominant swell



Fig. 12. Stingray device.

with a locally-generated wind sea acting in adifferent direction to produce a quilted pattern onthe water’s surface.

The energy stored in a unit area of sea isproportional to the wave height squared and theaverage energy per unit area may be calculated as:

1 rg[1] E�23 1344�

T

0y(t)2dt

2 T

where r is the water density (usually taken as 1.025 kg/m3 for sea water), g is gravitational acceleration(9.81 m/s2), T is the time over which the energy isaveraged and y(t) is the time-varying water elevation.

For any particular wave record taken over a time T,the water elevation y may be represented, via a Fourieranalysis, as the sum of a set of harmonic waves so that:

[2] y(t)�N

�n�1

Ancos(nwt �en)

where w is the wave angular frequency in radians/s,and N is the number of Fourier components. Theexpression for stored energy per unit area may then bewritten in the frequency domain as:

1 A(w)2[3] E �22443 rg

�

�0

2233441 dw2p T

The expression S(w)�A(w)2�pT is defined as theSpectral Energy Density (SED, in m2�s) so that thesurface energy per unit area may then be written as:

1[4] E�23 rg�

�

0S(w)dw

2

Waves energy propagate across the water surfacewith a velocity, described as the energy propagation orgroup velocity Cg, which varies with wave frequency.Mathematically Cg�dw�dk, where the wavelength (l)at a particular frequency is related to the wave numberk by the equation k�2p�l.

In the time domain, if the surface energy E at aparticular frequency, moves forward at a velocity Cg

then the amount of energy per unit time crossing a 1 mlong line perpendicular to the direction of wavepropagation is equal to ECg. This is the powertransmitted by the wave at that frequency. In thefrequency domain this power may be calculated as:

1[5] Pi�

23 rg��

0S(w)Cg(w)dw

2

Thus, to calculate available wave power from a setof wave data it is necessary to know the SED and thegroup velocity. The group velocity varies as a functionof wave frequency and water depth (h). In a finitewater depth the relationship w2/g�ktanh(kh) must besolved iteratively to determine k as a function of wavefrequency. In very deep water tanh(kh)��1 so that thissimplifies to w2/g�k.

If time series data is available for waterelevation at a particular location, then a Fourieranalysis may be performed to determine S(w). It isnoted that a Fourier analysis of typical wave datawill generally produce a ‘noisy’ curve of SED andit is normal to perform a smoothing operation. Adescription of different smoothing techniques isgiven by Chakrabarti (1988).

In practice, time series data is rarely availableand as an alternative, a range of ‘synthetic’ spectrahave been developed based upon long-termobservation. These spectra assume that the sea canbe described as a stationary random process whichmeans that they are representative of a relativelyshort period which is typically taken as 1/2 hour upto 10 hours. The majority of mathematical spectralmodels follow the form S(w)�B(w)�pexp(�Cw�q)where B, C, p and q are parameters whichdetermine the spectral form. This general form isreferred to as a four-parameter model.

Many wave spectra in common use may bedescribed by just two independent parameters relatingto wave height and wave frequency and anon-dimensional constant which varies as a functionof the wave frequency. The general form of thistwo-parameter model is:

A w344 4 w

[6] S(w)�23Hs2134 exp��A�1�

�4

�4 w5 w344

where A is the non-dimensional constant, Hs thesignificant wave height, and w

344

the characteristicfrequency for the spectrum.

Spectral moments are defined as:

[7] mn��

0wnS(w)dw

thus the zeroth moment is m0�∫�

0S(w)dw and isequivalent to the area under the SED curve.



Fig. 13. Underwater Electric Kite (courtesy of the UEK Corporation).

The significant wave height is defined byHs�4(m0)1/2. This is equivalent to four standarddeviations of the water elevation.

The spectral moments may be used to determineother properties of the spectrum. For example, thesignificant wave period Ts�2pm0�m1 and the zeroup-crossing period Tz�2p(m0�m2)1/2.

An earlier definition of significant wave heightwas that it was equal to the average height of thehighest one third of individual waves within aspectrum and was so chosen because the valueobtained appeared to correlate with the waveheight reported by a trained observer. Thesignificant wave period was similarly defined asthe average period of the highest one third ofwaves within a spectrum.

Models for fully-developed seas have beendeveloped by (amongst others) Pierson andMoskowitz (P-M), Bretschneider, the InternationalShip and offshore Structures Congress (ISSC) andthe International Towing Tank Conference (ITTC).They give similar results and the parameters for thetwo-parameter model are as defined in Table 3.This table includes the following parameters: A,non-dimensional coefficient; w

344

, mean frequency;wz, zero-crossing frequency; w0, peak frequency;ws, significant frequency.

To allow for a modification of the spectral shapeand peaked ness in seas which were not fullydeveloped, the JONSWAP spectrum was developedby Hasselmann, as part of the Joint North Sea WaveProject (Hasselmann et al. 1973). The P-M formulationwas modified to give:

w[8] S(w)�ag2w�5exp��1,25�12�

�4

� �w0

(w �w0)2

gexp��1113�2t2w02

The peaked ness parameter g (kurtosis) can varyfrom 1 to 7 but is typically 3.3.

The shape factor t is taken as 0.07 for w�5.24/Tz

and 0.09 for w�5.24/Tz.

The parameter a�0.076X0�0.22 where X0 is the

non-dimensional fetch defined as X0�gX�U 2w, X is the

fetch (m) and Uw is the prevailing wind velocityduring the development of the waves.

In the absence of specific site data, waveenergy developers will typically assume that thewave climate at a particular site may berepresented by a series of P-M or Bretschneiderspectra. This assumes a fully-developed wave field,which is reasonable, given that developers willnormally wish to site their devices in exposedlocations with maximum incident energy. Anexample of the SED of a Bretschneider spectrumwith Tc�9 s and Hs�2 m is shown in Fig. 14. Thepower in kW per metre of wave front for eachone-second period band centred on an integralnumber of seconds is also shown in this figure.These values integrate to 18.0 kW/m which is thetotal power in the sea. It is seen that, as aconsequence of the group velocity increasing withperiod, the peak of the power curve is at a longerperiod than that of the SED curve.

To maximize the performance of a wave energydevice it is necessary to optimize the response of thewave energy collector as a function of wave periodwith respect to the distribution of power, by period,within the sea.

As part of the development of a wave energycollector it is typical, in the first instance, to assessthe likely potential of the device by estimating itscapture efficiency as a function of frequency. Thiscan be done either via wave tank testing in regularwaves or by applying a mathematical model. In theearly stages of development, mathematical modelstend to rely on linear theory.

Developers are often interested in the‘efficiency’ of the power capture device and thesubsequent conversion of wave power to electricity.For this reason, capture performance is often non-dimensionalized. For example, in the case of OWCdevices, a capture factor (CF) may be defined asCF�W�Pid where W is the power captured by thewave energy collector, Pi is the incident power in



Table 3. Constants for 2-parameter models

Model A wz wz �w0 wz �w344 wz �ws

Pierson-Moskowitz (P-M) 1.25 w0 1.0 0.772 0.710

Bretschneider 0.675 ws 1.167 0.90 0.829

ISSC 0.4427 w344 1.296 1.0 0.921

ITTC 1.25 w0 1.0 0.772 0.710

kW/m and d is a dimension representative of thedevice. In the case of an OWC the representativedimension is usually taken as the width of thecollector opening. An example of capture factorsmeasured in regular wave testing of a cliff-mounted shoreline device is shown in Fig. 15. It isseen that the capture is poor at both short and longperiods but that at a 10-second period the capturefactor is much greater than unity. This means thatthe collector is capturing power from a width ofwave front that is broader than the device. In effect,it is acting as a focussing device for wave energyand drawing power into itself. Clearly, if thecollector were infinitely wide then this could nothappen as there would be nowhere from whence todraw the extra power but, as the size of a collectorreduces, it becomes increasingly easy to obtaincapture factors greater than unity (and an apparentefficiency greater than 100%). The ability ofincreasingly smaller units to capture power from awave front greater than their size is known as thepoint absorber effect. Evans (1980) demonstratedthat the magnitude of the point absorber effect islimited to the lower of l�2pd or 2, whichever is the

smaller; where l is the incoming wavelength and dthe device width.

It should be noted that since the capture factor isdefined on an arbitrary representative length, theinterpretation of capture factor as collector efficiencyis at best misleading. Whilst the non-dimensionalcapture factor is an extremely useful parameter forcomparing similar devices, it bears no firmrelationship to the size of a general collector structureor, more importantly, the cost of producing power fromthe waves. As such, there is no correlation betweencapture factor, or apparent efficiency, and the absoluteeffectiveness of a particular collector. It might be, forexample, that a low efficiency, low cost collectorproduces power more economically than a highefficiency, high cost unit.

If the capture factor of the collector is known asa function of wave period and the available wavepower in each period band is also known, then theabsolute power capture from each spectrum may becalculated as W=CFPi. An individual spectrumwill, however, only give the distribution of powerfor a short duration and is unlikely to berepresentative of the annual average performance.



tota

l pow

er (

kW)

SE

D (

m2 .

s)

0

0.6

0.5

0.4

0.2

0.1

0.3

0

0.5

1.0

1.5

2.0

2.5

3.0

wave period (s)

SEDpower in1 second band

0 5 10 15 20

Fig. 14. Example of a Bretschneider spectrumof SED with Tc�9 s, Hs�2 m water depth.

capt

ure

fact

or

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

period (s)5 7 9 11 13

Fig. 15. Capture factors 10 m wide shoreline OWC.

To give such an estimate of annual averageperformance, the power distribution as a functionof period for the whole year must be determinedand the device capture factors applied to thosedata. Annual (and seasonal) wave data are typicallyavailable in the form of a scatter diagram in whichthe proportionate occurrence of combinations ofwave height and period are recorded.

6.3.5 Environmental impact of wave and tidal devices

Although a key driver for the development of waveand tidal power plants is climate change and theneed to produce clean, green energy, there is alocal environmental impact that has to beconsidered. The local environmental impact isconcerned with the immediate surroundingphysical and socio-environmental changes that willor may occur if development in the coastal orocean waters takes place. There are many impactsto take into consideration: a) recognized shippingroutes and sea lanes; b) vessel safety; c) militarymovements; d ) security of supply; e) changes inwater and sediment movement; f ) grid cableroutings; g) fishing. These require consideration ona global and local scale. Special planning todetermine ‘no development’ areas is an issuefacing all nations that wish to take advantage ofpotential wave and tidal developments.

Spatial planning should be three-dimensional(major users of the spatial area are the militarywho use submarines). The military will havespecial access and routing requirements anddesignated testing grounds. They have an issue inspecifying ‘no-go’ areas as a result of theinformation they are putting into the publicdomain. There is also the major issue of the pastdisposal of UneXploded Ordinance (UXO). All thedisposal grounds will have to be clearly identifiedto ensure the safe development of projects; whilewave and tidal generation is at an early stage ofdevelopment, there is a limited amount of specificexperience regarding the environmental impact.For early projects, the assessment of actual impactwill provide knowledge which will be used for thesuccessful planning of future larger developments.

Navigational risk has to be considered. The impactdepends on the type of device. Many devices will haveto be kept well away from major shipping routes.Some devices will operate on the seabed and allowshipping to continue unaffected. The need for markerbuoys, light and sound signals and possibly foghornswill have to be considered.

As far as other projects above the surface areconcerned, there are different issues that will need tobe addressed regarding the life cycle of marinerenewable energy plants. For example, during theconstruction and decommissioning phase, disturbanceof the seabed will be important, whilst during theoperational phase machinery noise, including turbo-generators, may be an issue.

Some of the features of wave and tidal devices areshared across a number of technologies while otherswill be specific. Features such as sub-sea cables,overhead transmission cables, foundations andmoorings are common across a number oftechnologies. Sub-sea cables can have electromagneticinteractions with fish especially Elasmobranches(sharks and rays). Deep burial can alleviate theproblem but adds to the cost and seabed disruption dueto excavation. During construction, maintenance orremoval there is also disturbance of sediment on theseabed.

Many sites which are suitable for wave and tidalenergy projects are remote from the centres ofconsumption, so there will be a requirement foroverland transmission lines. These transmission lineschange the landscape and cause visual impact. Thisissue is shared with other renewable energytechnologies, specifically onshore wind. In countrieswith high population densities this impact has becomea potential block in the development of somerenewable energy projects.

Deployment of structures, foundations and devicesin flow streams may influence the speed of water flowboth locally and globally. Seabed scouring or partialdeposits may increase or decrease both flows byinfluencing further impact. Feeding and breedinghabits of all types of wildlife could be influenced bythese changes.

Wave and tidal developments have to consider theirimpact on marine mammals and seabirds. There is apotential impact on migratory routes. For instance,grey whales would have to swim around devices ifthey were located on their coastal path. Pinnipeds(seals and sea lions) may attempt to haul out onto lowfreeboard floating wave energy converters. This canhave a negative impact on the local fishingcommunity. For some developments the potential fordisplacing breeding seabirds would be an issue whichought to be addressed.

Tidal barrages change estuarinehydrodynamics, including possible reduction of thetidal regime and changes to the patterns ofsedimentation and erosion. The resulting loss ofshoreline habitats and change in marine habitats,due to the development of brackish or freshwaterconditions and increased build-up of nutrients, can



also create a barrier to migratory fish, unlesssuitable fish passes are provided.

Rotary turbines in tidal stream devices couldpotentially injure sea mammals and fish, althoughwith large size units the risk is minimal due to therelatively low speed of the rotation of the turbines.

Shoreline plants or substations for offshore plantscan have a landscape and visual impact that needs tobe considered. The visual impact of near shore andoffshore devices depends on the distance from theshore and the height of the devices above sea level.Another aspect that needs to be considered is pollutionfrom debris, if devices break up, or from the leakageof hydraulic fluids.

In the case of larger wave energy developments,the effects on wave regime and any consequentialeffect on inshore habitats and shoreline sedimenttransport would have to be considered. Little work hasbeen done, to date, on the impact of energy extractionfrom the oceans. The question remains as to whensufficient energy extraction will result in majorimpacts such as a disturbance of littoral flow.

Access to fishing is a major issue to deal with, butdevelopment wave and tidal devices may also lead tothe creation of fish no take zones. These are areaswithin the marine energy development boundariesthat, due to the development of energy machines,prohibit fishing boats entering.

The advantage of this restriction, however, may beto provide ideal habitats for fish or marine life to breedand grow in an area that is protected from exploitation.The creation of artificial reefs may improve thepotential for shellfish and crustacean growth, andbring the additional benefit of shoreline protection in anatural way.

Environmental management must be done on aglobal, local and specific basis. Consideration forwildlife, socio-economic and other key stakeholdersmust be given. Balancing these environmental impactsare the environmental benefits of: a) the resultingreduction in climate change; b) fishery protection; c) cleaner fuel; d ) security of energy supply; e) fossilfuel replacement. On a local basis, each and everydevice will require environmental impact assessmentsto be performed. The construction impact, thedevice-operating characteristics and the operationalimpact will have to be investigated and appropriaterisk-mitigation measures introduced.

6.3.6 Global prospects for the energy industry

Marine renewables have the potential to be a majorsource of energy and could significantly impact the

way in which energy is generated, transported andutilized. However, the full potential and extractionmethodologies have yet to be developed.

The force field illustrated in Fig. 16 attempts todemonstrate that there are drivers and resisters tomarine energy evolving. To ensure the industrysucceeds, the drivers must be reinforced and theresisters/blockers must be removed, diluted orsatisfied.

With the world population growing and increasingenergy needs per capita, the demand for electricity isgreater than ever. The International energy outlook2004 (EIA, 2004) predicts, “From 2001 to 2025 totalworld consumption of marketed energy is expected toexpand by 54 per cent”.

Onshore planning approvals for energy projectsare becoming more difficult to obtain. Withincreasing pressure on valuable land resources, it isnatural that mankind should look to the renewableenergy in the oceans to provide some of the energysupply. As fossil fuels become a scarcer and morevaluable resource, emerging alternative fuels, such asmarine renewables and hydrogen, will increasinglyfeature in the global energy equation. Hydrogen is astorable fuel which is both sustainable and flexible inits use. Fuel cells technology is advancing at a rapidrate and the potential for a ‘hydrogen economy’ ismoving closer. Sustainability issues and theenvironmental impact associated with traditionalmeans of energy production mean that if thehydrogen revolution is to occur it will rely on the useof ‘green’ electricity. Therefore, not only does thefuture appear to demand that the marine renewableenergy industry will grow to produce power forcurrent electrical consumption but it will also supplya massive increase in power to produce hydrogen fortransport and heat use.

Clean water is another major potential user formarine renewable energy. As the opportunities fordeveloping new sources of water rapidly disappear,more clean water is being produced by desalination.Therefore, whilst current marine renewable projectsare focussing on electricity generation for grid supply,it is possible that in the future, the production ofdesalinated water to alleviate water shortages willbecome a major driver for the development of waveand tidal projects. As the number and size of wave andtidal energy projects increases, the technologyimprovements and economies of scale will result in thedecreased cost of energy from these sources. The waveand tidal energy industry development path is likely tobe as follows.

2000-2010: the technology years. New emergingtechnology ideas grow from research and developmentinstitutions. Some of these ideas are adopted by



technology development companies who take theseideas forward and build full-scale prototype powerplants. A selection of leading technologies willcommence work on small-scale marine energy parks.

2010-2015: the opening era. A select fewtechnologies will emerge that are attractive on bothenvironmental and economic grounds and the firstcommercial-scale power plants will evolve.

2015-2020: the growth phase. Confidence in thesuccess of the ‘opening era’ will follow, resulting inthe significant growth of new marine energy powerplants. Marine energy supply will be considered as asignificant player in the world’s energy portfolio.

Marine renewables have the potential forgenerating enormous quantities of power. Currentprojects are demonstrating viability and opening theway for future major developments. It could take 10 to15 years for marine renewables to be developed tosuch a stage where they will be the energy source ofchoice. This energy source has the potential to be thepowerhouse of the hydrogen economy, which couldtake 30 to 40 years to evolve and will form the basisfor a clean, renewable and sustainable future forgenerations to come.

References

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Clément A. et al. (2002) Wave energy in Europe: currentstatus and perspectives, «Renewable and Sustainable EnergyReviews», 6, 405-431.

Davies P.G. et al. (1985) Wave energy. The Department ofEnergy’s R&D Programme 1974-1983, UK Department ofEnergy-Energy Technology Support Unit.

EIA (US Energy Information Administration) (2004) Internationalenergy outlook 2004, Washington (D.C.), EIA.

European Wave Energy symposium: proceedings of aninternational symposium held in Edinburgh, Scotland, 21-24 July 1993 (1994), East Kilbride (UK), NEL-RenewableEnergy.

Evans D.V. (1980) Some analytic results for two and threedimensional wave-energy absorbers, in: Power from seawave: based on the proceedings of a conference on powerfrom sea waves, oganized by the Institute of mathematicsand its applications, and held at the University of Edinburghfrom June 26-28 1979, London, Academic Press, 213-249.

Folley M. et al. (2002) Performance investigations of theLIMPET counter-rotating wells turbine, in: Proceedingsof the 2nd Marine Renewable Energy conference, Newcastle,11-12 September.

Hasselmann K. et al. (1973) Measurement of wind-wavegrowth and swell decay during the Joint North Sea WaveProject (JONSWAP), Hamburgh, Deutsche HydrographischeFeitschrift, 8-95.

Heath T. et al. (2000) The design, construction and operationof the LIMPET energy converter (Islay, Scotland), in:Proceedings of the 4th European Wave Energy conference,Aalborg (Denmark), 4-6 December.

Lagstroem G. (1999) SeaPower International. Floating WavePower Vessel, FWPV, in: Wave power. Moving towardscommercial liability. Proceedings of the IMECHE seminar,London.



climate change technology development availability

declining fossil fuel supply cost of energy from non-renewables e.g. fossil fuels

security of supply higher awareness of public choice

cleaner fuel planning and consultation, legislation, stakeholders

new energy demands lack of interest (someone else’s problem)

green power lobby groups non-aligned national/international agendas

new socio-economic development lack of funding, investment

environmental protection agencies

alternative energy lobbies e.g. nuclear

total of pushing forces total of resistance forces

drivers resisters/blockers

Fig. 16. The force field diagram for change.

Thorpe T.W. (1998) An overview of wave energy technologies,Report produced for the UK Office of Science andTechnology, AEA Technology Report AEAT-3615.

Thorpe T.W. (1999) A brief review of wave energy, Reportproduced for the UK Department of Trade and Industry,AEA Technology Report ETSU-R-120.

UK Office of Science and Technology (1999) Energiesfrom the sea. Towards 2020: a marine foresight panel report,Report 99/501.

Vriesema B. (1995) The Archimedes wave swing: a new wayof utilising wave energy, ECN Energie Efficiency ReportECN-I-95-030.

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Yemm R. (2003) Pelamis WEC. Intermediate Scale Demonstration,UK DTI New and Renewable Energy Programme, ReportV/06/00188/00/00.

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