Marine EnergyMarine Energy

Dr Gareth HarrisonDr Gareth HarrisonUniversity of EdinburghUniversity of Edinburgh

OverviewOverview

•• What is marine energy?What is marine energy?•• Wave powerWave power•• Tidal powerTidal power

Marine EnergyMarine Energy

•• Marine energy covers all methods for Marine energy covers all methods for extracting energy from the oceansextracting energy from the oceans–– Wave powerWave power–– Tidal powerTidal power–– Ocean Thermal Energy Conversion (OTEC)Ocean Thermal Energy Conversion (OTEC)

Wave Power Wave Power

Wave PowerWave Power

•• The UK is exposed to Atlantic waves The UK is exposed to Atlantic waves incident from the west and south westincident from the west and south west

•• These waves are generated by the These waves are generated by the predominant winds blowing across the predominant winds blowing across the Atlantic FetchAtlantic Fetch

•• There was a major UK R&D programme in There was a major UK R&D programme in the late 70s to early 80s the late 70s to early 80s

•• Renewed interest in the 1990sRenewed interest in the 1990s

Wave GenerationWave Generation

In effect, the Atlantic acts as an enormous wind energy converter

W I N DW I N DW

A V E S

W A V E S

Wave GenerationWave Generation•• Waves at sea generated by friction Waves at sea generated by friction

between wind and water surfacebetween wind and water surface•• Transfer of energy from the wind Transfer of energy from the wind

to the water to the water • Sea surface shape becomes

unstable • Wind creates differential pressure

distribution and waves grow

• The term Hsig, or Significant Height, is used to describe the ‘size’ of waves

• Hsig is average value of the biggest third of the observed waves

Water Surface

Motion of seawater

wind

Wind

water movementfrom high to low pressure

+

+

_

_

Watersurface

The Energy in a WaveThe Energy in a Wave•• Energy is being continually Energy is being continually

transformed from kinetic to potential transformed from kinetic to potential and back again. and back again.

•• Particles move in circular paths, known Particles move in circular paths, known as as orbitalsorbitals. .

•• The diameter of the The diameter of the orbitalsorbitals decreases decreases rapidly as one descends below the sea rapidly as one descends below the sea surface. surface.

•• Hence, any device designed to harness Hence, any device designed to harness energy in waves should lie at or close energy in waves should lie at or close to the sea surfaceto the sea surface

direction of wave propogation

95% of theenergy in awave is within1/4 of awavelengthfrom thesurface

Power (watts per metre)

water density

gravitational acceleration

wave height

wave period

eg: 3m height and 10 second period: P = 90kW/m

Wave PowerWave Power

Mean solar radiation: 350Wm-2

Mean wind power transfer to waves <1Wm-2

World wave power densities in kilowatts per metre (kW/m)

sun – wind - waves

Wave ResourceWave Resource

Wave ResourceWave Resource

•• Possible to express the Possible to express the mean annual wave mean annual wave energy flux density energy flux density around the UKaround the UK

•• Atlas of UK Marine Atlas of UK Marine Renewable Energy Renewable Energy Resources is an Resources is an invaluable source of invaluable source of preliminary datapreliminary data

>40kW/m

Wave resource is highest during the winter months.

These are also the periods of highest energy demand across the UK

Wave Power Wave Power -- Offshore or CoastalOffshore or Coastal

OffshoreOffshore•• Exploit the Exploit the

massive resource massive resource of the North of the North AtlanticAtlantic

CoastalCoastal•• Utilise the more Utilise the more

modest but modest but accessible coastal accessible coastal resourceresource

Tethered Buoyant StructuresTethered Buoyant Structures

•• Essentially free floating objects whose motion is Essentially free floating objects whose motion is restricted by a mooring system, which incorporates some restricted by a mooring system, which incorporates some form of power extraction system.form of power extraction system.

Energy Extraction device

“Free” Floating Object

Relative Motion DevicesRelative Motion Devices

•• Devices in which energy is extracted via the relative Devices in which energy is extracted via the relative motion of different parts of an extended structure. motion of different parts of an extended structure.

Energy extracted via therelative motion of hingedelements

A more exotic version of this principle might involve the use of motion relative to internal gyroscopes as proposed for the Salter Duck.

Pelamis is an example of this.

The DuckThe Duck

Flexible Membrane DevicesFlexible Membrane Devices

•• In this family of devices, characterised by the Clam, the In this family of devices, characterised by the Clam, the pressure under a wave is used to compress air, which is pressure under a wave is used to compress air, which is then driven through low pressure turbines.then driven through low pressure turbines.

sealedflexiblemembrane

encloseddevicestructure

Enclosed Water Column DevicesEnclosed Water Column Devices•• These devices are philosophically related to the flexible These devices are philosophically related to the flexible

membrane types, in that they use water pressure to membrane types, in that they use water pressure to drive air through a turbine, but they rely on the air water drive air through a turbine, but they rely on the air water interface itself to act as the pressure mechanism. interface itself to act as the pressure mechanism.

•• This type of device is already in commercial use, most This type of device is already in commercial use, most notably in Japan, to power navigation buoys.notably in Japan, to power navigation buoys.

air flow

incoming wave semi encloseddevice structure

Large Scale PrototypesLarge Scale Prototypes•• Pelamis (Ocean Power Delivery Ltd) Pelamis (Ocean Power Delivery Ltd)

–– An articulated relative motion device rated at 750kWAn articulated relative motion device rated at 750kW

Wave DragonWave DragonA floating system which uses reflectors to direct the sea water into a storage lagoon.Prototype has a rated power of 20kW. It is approximately 58m by 33m in size.

© Earth-vision.biz

© Wave Dragon ApS© Wave Dragon ApS

Large Scale PrototypesLarge Scale Prototypes•• Archimedes Wave SwingArchimedes Wave Swing

–– Uses a buoyant float chamber which moves relative to Uses a buoyant float chamber which moves relative to a base on the sea bed. a base on the sea bed.

–– A prototype rated at 2MW is being tested in Portugal A prototype rated at 2MW is being tested in Portugal after a delayed launch in 2004.after a delayed launch in 2004.

System under tow to installation site Being sunk into position

Other Wave DevicesOther Wave DevicesThe Aquabuoy(Aqua Energy)The Powerbuoy (Ocean Power Technology)

CRE+E

Coastal Wave Energy InstallationsCoastal Wave Energy Installations

•• Wave power density in coastal waters lower due Wave power density in coastal waters lower due to friction with sea bed to friction with sea bed –– 50kW/m in deep water drop to 20kW/m in shallow 50kW/m in deep water drop to 20kW/m in shallow

water water

•• Reduced storm powerReduced storm power•• Robust devices if fixed to the seaRobust devices if fixed to the sea--bed or cliffsbed or cliffs•• Electricity connection costs lowerElectricity connection costs lower•• Maintenance costs lowerMaintenance costs lower

Technology Options for Coastal Technology Options for Coastal Wave Power SystemsWave Power Systems•• Two principal technologies suited to Two principal technologies suited to

coastal wave energy developments: coastal wave energy developments: –– The enclosed water column devices already The enclosed water column devices already

mentioned for deep water applications andmentioned for deep water applications and–– Tapered channel systemsTapered channel systems

Enclosed Water Column Devices Enclosed Water Column Devices in Coastal Watersin Coastal Waters

•• Stable fixing Stable fixing •• Location in gully to Location in gully to

maximise the effect of maximise the effect of wave focusingwave focusing

incomingwave energy water column

device

rock gulley

in and outflowof lowpressure air

rise and fallof watersurface

The Tapered Channel ConceptThe Tapered Channel Concept

•• The tapered channel The tapered channel is uniquely applicable is uniquely applicable to a coastal to a coastal developmentdevelopment

•• The energy of a The energy of a wave is used to lift wave is used to lift water up an artificial water up an artificial channel into an channel into an artificial pondartificial pond

•• Drain back down to Drain back down to sea level through a sea level through a low head water low head water turbineturbine

incoming wave

channel

water rushing up channel

“storage pond”

incoming wave energy

storage pondchannel

••Tapered ChannelTapered Channel

Tidal Power Tidal Power

The TidesThe Tides

DefinitionDefinition•• The rise and fall of the ocean surface The rise and fall of the ocean surface

under the influence of the gravitational under the influence of the gravitational and dynamic influence of the and dynamic influence of the Earth/Moon/Sun systemEarth/Moon/Sun system

•• The first effective theory was produced by The first effective theory was produced by NewtonNewton

•• Attraction of Moon and Sun means water tends to bulge Attraction of Moon and Sun means water tends to bulge on side of Earth nearest Moon and on opposite sideon side of Earth nearest Moon and on opposite side

•• As the Earth rotates the tidal bulges try to maintain As the Earth rotates the tidal bulges try to maintain position relative to Moon and travel round the Earth in 24 position relative to Moon and travel round the Earth in 24 hours hours

•• The MoonThe Moon’’s orbit means the period is 24 hours and 50 s orbit means the period is 24 hours and 50 minutes minutes

Earth

tidal bulge

Moon

The TidesThe Tides

SunSun’’s Influences Influence

Moon

Earth

Lunar tide

solar tide

Sun

Moon and Sun reinforce each other to produce large tides known as Spring Tides

A similar effect at Full Moon.

New Moon New Moon -- ““Spring TideSpring Tide””

SunSun’’s Influences Influence

When the Sun and Moon are at 90o to each other, the effect is of cancellation as shown.

Moon

Earth

Lunar tide

solar tide

Sun

This configuration results in Neap Tides

Half Moon Half Moon –– ‘‘Neap TidesNeap Tides’’

Tidal Structure

Land and sea Land and sea depth and depth and CoriolisCoriolisforce strongly force strongly affect the tidesaffect the tides

Energy in the TidesEnergy in the Tides•• Total energy from the tides dissipated through friction Total energy from the tides dissipated through friction

estimated at 3000 GW 1000 GW available in relatively estimated at 3000 GW 1000 GW available in relatively shallow coastal regions shallow coastal regions

•• Achievable worldwide electrical power extraction Achievable worldwide electrical power extraction estimated as 120 estimated as 120 -- 400 GW; (UK 36400 GW; (UK 36--50 50 TWhTWh))

Extracting Energy : Tide MillsExtracting Energy : Tide Mills

•• The extraction of The extraction of energy from the tides energy from the tides is not a new idea is not a new idea

•• Mills, using tidal Mills, using tidal flows in bays and flows in bays and estuaries to drive estuaries to drive machinery to grind machinery to grind cereal were used in cereal were used in Middle Ages in Middle Ages in EnglandEngland

•• Rare after First World Rare after First World WarWar

Tidal Barrage SystemsTidal Barrage Systems

•• Essentially modern electrical generation developments of Essentially modern electrical generation developments of the traditional tide millthe traditional tide mill

•• In the nineteenth and twentieth centuries, there were In the nineteenth and twentieth centuries, there were numerous proposals to exploit the tidal energy potential numerous proposals to exploit the tidal energy potential of the Severn Estuary. None have yet been developed. of the Severn Estuary. None have yet been developed.

•• The world's first serious scheme to exploit tidal energy The world's first serious scheme to exploit tidal energy was constructed in France, at La Rance in Brittany, was constructed in France, at La Rance in Brittany, between 1961 and 1967 and consists of a barrage across between 1961 and 1967 and consists of a barrage across a tidal estuary to utilise the rise and fall in sea level a tidal estuary to utilise the rise and fall in sea level induced by the tides. induced by the tides.

Tidal Barrages

head

flow ofwaterthroughturbines

turbine andgenerator

possible roadlink

Tidal Barrage SystemsTidal Barrage Systems

•• Designed to harness the rise and fall of Designed to harness the rise and fall of the sea by enclosing tidal estuaries the sea by enclosing tidal estuaries egeg

•• LaRanceLaRance, Severn, Solway, Severn, Solway

Single Basins

enclosed basin

barrage

openwater

sluices

Gated turbines

La La RanceRance Tidal BarrageTidal Barrage

•• First serious tidal First serious tidal scheme constructed at scheme constructed at La La RanceRance in Brittany, in Brittany, France in 1961 France in 1961 -- 1967 1967

•• It consists of a barrage It consists of a barrage across a tidal estuary to across a tidal estuary to utilise the rise and fall utilise the rise and fall in sea level induced by in sea level induced by the tides the tides

•• This scheme has proven This scheme has proven itself to be highly itself to be highly successful despite some successful despite some early teething problemsearly teething problems

Site mean tidal range

(m)

Barrage

length (m)

estimated annual energy

production (GWh)

Severn Estuary(UK) 7.0 17,000 12,900

Solway Firth (UK) 5.5 30,000 10,050

Bay of Fundy

(Canada)

11.7 8,000 11,700

Gulf of Cambay

(India)

6.1 25,000 16,400

Possible Sites WorldwidePossible Sites Worldwide

Tidal Barrage DevelopmentTidal Barrage Development

• The Severn Estuary could provide in excess of 8% of the UK’s requirement for electrical energy

• Long construction times make them expensive

• Potentially serious environmental impacts

• It is anticipated that public and political opposition will limit the development of tidal barrage schemes in the short term

Tidal CurrentsTidal Currents•• Typically small in the open oceanTypically small in the open ocean•• Local geographical effects can enhance flow speeds Local geographical effects can enhance flow speeds

Key European sites: Pentland Firth (Scotland), Straits of MessinKey European sites: Pentland Firth (Scotland), Straits of Messinaa

Tidal Current DevicesTidal Current Devices•• Must convert energy in moving water into Must convert energy in moving water into

mechanical movementmechanical movement–– Horizontal axis devicesHorizontal axis devices–– Vertical axis devicesVertical axis devices–– Linear lift devicesLinear lift devices–– Venturi devicesVenturi devices

•• Must be held in place against fluid loadingMust be held in place against fluid loading–– Fixed to sea bedFixed to sea bed–– Anchored floatingAnchored floating

Tidal Conversion ConceptsTidal Conversion Concepts

Tidal flow

rotationalaxisTidal flow

rotational axis

Horizontal axis turbine Vertical axis turbine

Venturi based device Linear lift based device

Vertical Axis TurbinesVertical Axis Turbines

•• The rotational axis of The rotational axis of the system is the system is perpendicular to the perpendicular to the direction of water flowdirection of water flow

•• A horizontal axis A horizontal axis turbine has the turbine has the traditional form of traditional form of ““fanfan”” type system type system familiar in the form of familiar in the form of wind turbineswind turbines

Horizontal Axis TurbinesHorizontal Axis Turbines

Technology options: Technology options: holding a turbine in placeholding a turbine in place

Shallow water options Deeper water options

Loch Linnhe TurbineLoch Linnhe TurbineSmall floating demonstration device in the early 1990s

Study conducted by IT Power Ltd and funded by Scottish Nuclear

Prototype SystemsPrototype SystemsENERMAR

Tested in 2000 in the Strait of Messina (between Sicily and the Italian mainland)A large vertical axis floating generator

CRE+E

Prototype DevicesPrototype Devices•• SeaFlow (Marine Current Turbines Ltd)SeaFlow (Marine Current Turbines Ltd)•• Rated power output of 300kW, Rated power output of 300kW, •• mounted on a vertical pillar fixed into mounted on a vertical pillar fixed into

the sea bed. the sea bed. •• In Bristol Channel off LynmouthIn Bristol Channel off Lynmouth

Prototype DevicesPrototype Devices•• Stingray (The Engineering Business Ltd)Stingray (The Engineering Business Ltd)•• Tested in Yell Sound, Shetland during 2002 to 2003 Tested in Yell Sound, Shetland during 2002 to 2003 •• Uses a unique linear foil systemUses a unique linear foil system•• Novel barge based installation systemNovel barge based installation system

Stingray awaiting installation in Yell Sound Artists impression of Stingray

Prototype DevicesPrototype Devices•• Hammerfest StromHammerfest Strom

–– Grid connected, sea bed mounted horizontal axis Grid connected, sea bed mounted horizontal axis system which was installed in Norway in 2003. system which was installed in Norway in 2003.

Artists impression Installation process

Systems under developmentSystems under development

60kW device being installed

Hydroventuri LtdEnergy extraction system based upon utilisation of the pressure differential created in a venturi

Lunar Technology LtdUses a horizontal axis turbine in a protective/flow enhancing cowl

1.5MW device concept

Systems under developmentSystems under development

•• TiDel (SMD TiDel (SMD HdrovisionHdrovision))–– Tethered twin horizontal Tethered twin horizontal

axis systemaxis system

The Sea SnailThe Sea Snail•• Support system for tidal Support system for tidal

energy extraction energy extraction systemssystems

•• ““minimalminimal”” sea bed sea bed preparationpreparation

•• System is prefabricated System is prefabricated requiring minimal onrequiring minimal on--site site constructionconstruction

•• Installation requires the Installation requires the use of a tuguse of a tug

•• ““EasilyEasily”” removed for removed for maintenance, etc.maintenance, etc.

Kinetic Energy in Moving WaterKinetic Energy in Moving Water

A(m2)

U(r)r

ρ is the water density (kg/m3)

A is the cross sectional area of the channel (m2) and

U is the component of the fluid flow velocity (m/s)

3

A21 UAP ρ=

Influence of Flow Speed on Energy Flux

0

5

10

15

20

25

30

35

0 1 2 3 4

Flow Speed (m/s)

Pow

er D

ensi

ty (K

W/m

2)

0

200

400

600

800

1000

1200

1400

Ene

rgy

Flux

(MW

)

Influence of Flow Speed on Energy Influence of Flow Speed on Energy Flux in a Simple ChannelFlux in a Simple Channel

40m40mChannel DepthChannel Depth

1000m1000mChannel WidthChannel Width

Mean consumption: Edinburgh

Tidal Current Energy Flux DensityTidal Current Energy Flux Density

Spring Tide Speed Predictions Neap Tide Speed Predictions

Advantages of Tidal CurrentAdvantages of Tidal Current

•• High energy densityHigh energy density

Small devicesSmall devices

•• Low visibilityLow visibility•• Predictable resourcePredictable resource

Suitability for energy storageSuitability for energy storage

Marine currents Marine currents -- energy intensityenergy intensity

A tidal current turbine gainsover 4x as much energy perm2 of rotor as a wind turbine

Visual ImpactVisual Impact

50 to 100MW / km2

10 to 20 MW / km2

marine current farm

wind farm

PredictabilityPredictability

Will Marine Energy be viable? Will Marine Energy be viable?

ScaleScale

•• UK Renewable TargetsUK Renewable Targets

201010% of all electrical energy generated in the UK should be from renewable sources

Equivalent to 14GW installed capacity(600MW at present)

Capital investment requirement of some £2billion per annum required

Up to 35,000 direct manufacturing and installation related jobs- not necessarily in the UK!

(8000 at present- DTI )

202020% generation targets

Equivalent to 35GW installed capacity(assuming consumption continues to rise)

Capital investment needs to continue at £2billion per annum

At least 35,000 steady state jobs- not necessarily in the UK

Relative to windRelative to wind•• If onshore wind alone is used to meet the If onshore wind alone is used to meet the

2020 target, then some 1750km2020 target, then some 1750km22 of wind of wind farms will be needed!farms will be needed!

Area to be covered by onshore wind farms, if 2020 UK target is to be met

Economic ChallengesEconomic Challenges

•• Onshore wind can be economic as a result Onshore wind can be economic as a result of the sale of electricity and the trading of of the sale of electricity and the trading of Renewable Obligation CertificatesRenewable Obligation Certificates

•• Not yet the case for marine renewablesNot yet the case for marine renewables

Towards a Marine Renewable Industry Towards a Marine Renewable Industry

• Current estimated costs are too high• Once economies of scale apply costs will fall

© Scottish Executive

Who pays the up front costs before commercial viability?

Estimated requirement for under £200 million to kick start an industry

Scottish parliament cost £430 million!

Experience with wind

RewardsRewards

•• In Scotland alone (Scottish Executive figures)In Scotland alone (Scottish Executive figures)–– Direct employment of 7000 by 2020Direct employment of 7000 by 2020–– 10% of Scotland electricity from marine sources by 10% of Scotland electricity from marine sources by

20202020

•• (these figures do not consider the implications of (these figures do not consider the implications of a developing export industry)a developing export industry)

ChallengesChallenges

•• Survivability (wave)Survivability (wave)–– Devices must be able to survive the biggest waves, yet be Devices must be able to survive the biggest waves, yet be

sensitive to the more common , less extreme, seassensitive to the more common , less extreme, seas

•• Power smoothingPower smoothing–– Wave devices produce power which varies at wave frequenciesWave devices produce power which varies at wave frequencies–– Tidal produces Tidal produces ‘‘lumpylumpy’’ powerpower

•• ConnectionConnection (especially offshore floating systems)(especially offshore floating systems)–– Devices must be connected to the shoreline in potentially Devices must be connected to the shoreline in potentially

hostile watershostile waters

First commercial orderFirst commercial order

Povoa do Varzim

3 Pelamis units have been delivered to Portugal.

Currently being assembled at Peniche.

If successful, another 30 to follow.

Pelamis in PortugalPelamis in PortugalPovoa do Varzim

Leaving Stornoway In Portugal Welcomed in Portugal

ConclusionsConclusions

•• Marine energy offers a potentially large Marine energy offers a potentially large new renewable energy sourcenew renewable energy source

•• Lots of competing technologies Lots of competing technologies –– which which will win?will win?

•• Scotland needs to develop these to Scotland needs to develop these to generate economic rewardsgenerate economic rewards