Marine Energy Dr Gareth Harrison University of Edinburgh
Overview What is marine energy? Wave power Tidal power
Marine Energy Marine energy covers all methods for extracting energy from the oceans Wave power Tidal power Ocean Thermal Energy Conversion (OTEC)
Wave Power
Wave Power The UK is exposed to Atlantic waves incident from the west and south west These waves are generated by the predominant winds blowing across the Atlantic Fetch There was a major UK R&D programme in the late 70s to early 80s Renewed interest in the 1990s
Wave Generation W A V E S W I N D In effect, the Atlantic acts as an enormous wind energy converter
Wave Generation Motion of sea water wind Water Surface Waves at sea generated by friction between wind and water surface Transfer of energy from the wind to the water Sea surface shape becomes unstable Wind creates differential pressure distribution and waves grow + + Wind water movement from high to low pressure Water surface 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
The Energy in a Wave Energy is being continually transformed from kinetic to potential and back again. Particles move in circular paths, known as orbitals. The diameter of the orbitals decreases rapidly as one descends below the sea surface. Hence, any device designed to harness energy in waves should lie at or close to the sea surface direction of wave propogation 95% of the energy in a wave is within 1/4 of a wavelength from the surface
Wave Power water density gravitational acceleration wave height wave period Power (watts per metre) eg: 3m height and 10 second period: P = 90kW/m
Wave Resource sun wind - waves Mean solar radiation: 350Wm -2 Mean wind power transfer to waves <1Wm -2 World wave power densities in kilowatts per metre (kw/m)
Wave Resource >40kW/m Possible to express the mean annual wave energy flux density around the UK Atlas of UK Marine Renewable Energy Resources is an invaluable source of preliminary data
Wave resource is highest during the winter months. These are also the periods of highest energy demand across the UK
Wave Power - Offshore or Coastal Offshore Exploit the massive resource of the North Atlantic Coastal Utilise the more modest but accessible coastal resource
Tethered Buoyant Structures Essentially free floating objects whose motion is restricted by a mooring system, which incorporates some form of power extraction system. Free Floating Object Energy Extraction device
Relative Motion Devices Devices in which energy is extracted via the relative motion of different parts of an extended structure. Energy extracted via the relative motion of hinged elements Pelamis is an example of this. A more exotic version of this principle might involve the use ofmotion relative to internal gyroscopes as proposed for the Salter Duck.
The Duck
Flexible Membrane Devices In this family of devices, characterised by the Clam, the pressure under a wave is used to compress air, which is then driven through low pressure turbines. sealed flexible membrane enclosed device structure
Enclosed Water Column Devices These devices are philosophically related to the flexible membrane types, in that they use water pressure to drive air through a turbine, but they rely on the air water interface itself to act as the pressure mechanism. This type of device is already in commercial use, most notably in Japan, to power navigation buoys. air flow incoming wave semi enclosed device structure
Large Scale Prototypes Pelamis (Ocean Power Delivery Ltd) An articulated relative motion device rated at 750kW
Wave Dragon Earth-vision.biz A 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. Wave Dragon ApS Wave Dragon ApS
Large Scale Prototypes Archimedes Wave Swing Uses a buoyant float chamber which moves relative to a base on the sea bed. A prototype rated at 2MW is being tested in Portugal after a delayed launch in 2004. System under tow to installation site Being sunk into position
CRE+E Other Wave Devices The Powerbuoy(Ocean Power Technology) The Aquabuoy(Aqua Energy)
Coastal Wave Energy Installations Wave power density in coastal waters lower due to friction with sea bed 50kW/m in deep water drop to 20kW/m in shallow water Reduced storm power Robust devices if fixed to the sea-bed or cliffs Electricity connection costs lower Maintenance costs lower
Technology Options for Coastal Wave Power Systems Two principal technologies suited to coastal wave energy developments: The enclosed water column devices already mentioned for deep water applications and Tapered channel systems
Enclosed Water Column Devices in Coastal Waters Stable fixing Location in gully to maximise the effect of wave focusing incoming wave energy rock gulley water column device in and outflow of low pressure air rise and fall of water surface
The Tapered Channel Concept The tapered channel is uniquely applicable to a coastal development The energy of a wave is used to lift water up an artificial channel into an artificial pond Drain back down to sea level through a low head water turbine incoming wave incoming wave energy water rushing up channel storage pond channel channel storage pond
Tapered Channel
Tidal Power
The Tides Definition The rise and fall of the ocean surface under the influence of the gravitational and dynamic influence of the Earth/Moon/Sun system The first effective theory was produced by Newton
The Tides Attraction of Moon and Sun means water tends to bulge on side of Earth nearest Moon and on opposite side As the Earth rotates the tidal bulges try to maintain position relative to Moon and travel round the Earth in 24 hours The Moon s s orbit means the period is 24 hours and 50 minutes Earth Moon tidal bulge
Sun s s Influence New Moon - Spring Tide Earth solar tide Lunar tide Moon Sun Moon and Sun reinforce each other to produce large tides known as Spring Tides A similar effect at Full Moon.
Sun s s Influence Half Moon Neap Tides When the Sun and Moon are at 90 o to each other, the effect is of cancellation as shown. Moon Earth solar tide Sun This configuration results in Neap Tides Lunar tide
Tidal Structure Land and sea depth and Coriolis force strongly affect the tides
Energy in the Tides Total energy from the tides dissipated through friction estimated at 3000 GW 1000 GW available in relatively shallow coastal regions Achievable worldwide electrical power extraction estimated as 120-400 GW; (UK 36-50 TWh)
Extracting Energy : Tide Mills The extraction of energy from the tides is not a new idea Mills, using tidal flows in bays and estuaries to drive machinery to grind cereal were used in Middle Ages in England Rare after First World War
Tidal Barrage Systems Essentially modern electrical generation developments of the traditional tide mill In the nineteenth and twentieth centuries, there were numerous proposals to exploit the tidal energy potential of the Severn Estuary. None have yet been developed. The world's first serious scheme to exploit tidal energy was constructed in France, at La Rance in Brittany, between 1961 and 1967 and consists of a barrage across a tidal estuary to utilise the rise and fall in sea level induced by the tides.
Tidal Barrage Systems Designed to harness the rise and fall of the sea by enclosing tidal estuaries eg LaRance,, Severn, Solway Single Basins Tidal Barrages open water barrage sluices enclosed basin possible road link turbine and generator head Gated turbines flow of water through turbines
La Rance Tidal Barrage First serious tidal scheme constructed at La Rance in Brittany, France in 1961-1967 It consists of a barrage across a tidal estuary to utilise the rise and fall in sea level induced by the tides This scheme has proven itself to be highly successful despite some early teething problems
Possible Sites Worldwide 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 11.7 8,000 11,700 (Canada) Gulf of Cambay (India) 6.1 25,000 16,400
Tidal 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 Currents Typically small in the open ocean Local geographical effects can enhance flow speeds Key European sites: Pentland Firth (Scotland), Straits of Messina
Tidal Current Devices Must convert energy in moving water into mechanical movement Horizontal axis devices Vertical axis devices Linear lift devices Venturi devices Must be held in place against fluid loading Fixed to sea bed Anchored floating
Tidal Conversion Concepts Tidal flow rotational axis Tidal flow rotational axis Horizontal axis turbine Vertical axis turbine Venturi based device Linear lift based device
Vertical Axis Turbines The rotational axis of the system is perpendicular to the direction of water flow
Horizontal Axis Turbines A horizontal axis turbine has the traditional form of fan type system familiar in the form of wind turbines
Technology options: holding a turbine in place Shallow water options Deeper water options
Loch Linnhe Turbine Small floating demonstration device in the early 1990s Study conducted by IT Power Ltd and funded by Scottish Nuclear
Prototype Systems ENERMAR Tested in 2000 in the Strait of Messina (between Sicily and the Italian mainland) A large vertical axis floating generator CRE+E
Prototype Devices SeaFlow (Marine Current Turbines Ltd) Rated power output of 300kW, mounted on a vertical pillar fixed into the sea bed. In Bristol Channel off Lynmouth
Prototype Devices Stingray (The Engineering Business Ltd) Tested in Yell Sound, Shetland during 2002 to 2003 Uses a unique linear foil system Novel barge based installation system Stingray awaiting installation in Yell Sound Artists impression of Stingray
Prototype Devices Hammerfest Strom Grid connected, sea bed mounted horizontal axis system which was installed in Norway in 2003. Artists impression Installation process
Systems under development Hydroventuri Ltd Energy extraction system based upon utilisation of the pressure differential created in a venturi Lunar Technology Ltd Uses a horizontal axis turbine in a protective/flow enhancing cowl 60kW device being installed 1.5MW device concept
Systems under development TiDel (SMD Hdrovision) Tethered twin horizontal axis system
The Sea Snail Support system for tidal energy extraction systems minimal sea bed preparation System is prefabricated requiring minimal on-site construction Installation requires the use of a tug Easily removed for maintenance, etc.
Kinetic Energy in Moving Water P = 1 ρau 2 A 3 ρ is the water density (kg/m 3 ) A is the cross sectional area of the channel (m 2 ) and A(m 2 ) U is the component of the fluid flow velocity (m/s) r U(r)
Influence of Flow Speed on Energy Flux in a Simple Channel Channel Width Channel Depth 1000m 40m Influence of Flow Speed on Energy Flux 35 1400 Power Density (KW/m2) 30 25 20 15 10 5 Mean consumption: Edinburgh 1200 1000 800 600 400 200 Energy Flux(MW) 0 0 0 1 2 3 4 Flow Speed (m/s)
Tidal Current Energy Flux Density
Spring Tide Speed Predictions Neap Tide Speed Predictions
Advantages of Tidal Current High energy density Small devices Low visibility Predictable resource Suitability for energy storage
Marine currents - energy intensity A tidal current turbine gains over 4x as much energy per m 2 of rotor as a wind turbine
Visual Impact wind farm 10 to 20 MW / km 2 marine current farm 50 to 100MW / km 2
Predictability
Will Marine Energy be viable?
Scale UK Renewable Targets 2010 10% 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 ) 2020 20% 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 wind If onshore wind alone is used to meet the 2020 target, then some 1750km 2 of wind farms will be needed! Area to be covered by onshore wind farms, if 2020 UK target is to be met
Economic Challenges Onshore wind can be economic as a result of the sale of electricity and the trading of Renewable Obligation Certificates Not yet the case for marine renewables
Towards a Marine Renewable Industry Current estimated costs are too high Once economies of scale apply costs will fall Experience with wind 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! Scottish Executive
Rewards In Scotland alone (Scottish Executive figures) Direct employment of 7000 by 2020 10% of Scotland electricity from marine sources by 2020 (these figures do not consider the implications of a developing export industry)
Challenges Survivability (wave) Devices must be able to survive the biggest waves, yet be sensitive to the more common, less extreme, seas Power smoothing Wave devices produce power which varies at wave frequencies Tidal produces lumpy power Connection (especially offshore floating systems) Connection Devices must be connected to the shoreline in potentially hostile waters
First commercial order 3 Pelamis units have been delivered to Portugal. Currently being assembled at Peniche. If successful, another 30 to follow. Povoa do Varzim
Pelamis in Portugal Povoa do Varzim Leaving Stornoway In Portugal Welcomed in Portugal
Conclusions Marine energy offers a potentially large new renewable energy source Lots of competing technologies which will win? Scotland needs to develop these to generate economic rewards