Maori and the Sustainable Energy Business – 3-4 August 2005, Taupo Wave and Tidal Energy Richard Gorman National Institute of Water and Atmospheric Research
Contents • Waves and tides • Tidal energy technologies • The NZ tidal energy resource • Wave energy technologies • The NZ wave energy resource • Summary
Waves and tides • Tides vary on time scales of 6-12 hours (diurnal, semi-diurnal) • Surface wind-waves have periods of a few seconds • Tides are driven by gravitational attraction of moon and sun • Waves are created by winds blowing over the ocean
Tidal energy conversion • Underwater turbines • Hydroplane devices technologies • Tidal barrage
Rance Estuary Tidal Barrage • Rance Estuary, Brittany, France • Construction began in 1960, completed in 1967 • Dam length 330 m 22 km 2 basin • • Tidal range of 8m • Lock to allow passage for small craft • 24 turbines, each 5.4m diameter rated at 10MW were connected to the 225kV French Transmission network. • Bulb Turbines allow generation on both ebb and flood tides. • Turbines can also pump water into the basin • Total capacity 240MW, connected to French national grid • http://www.edf.fr
Tidal Power – SeaFlow turbine • Marine Current Turbines Ltd (UK) • Pilot plant installation in the Bristol Channel • horizontal axis turbine • http://www.mct.com
Tidal Power : Rotech Turbine • Rotech Tidal Turbine (RTT) • Bi-directional venturi shaped duct • Symmetrical turbine blades • Works with off-axis flows (<40 ° ) • Hydraulic transmission to generator • Power cable to shore • 1MW Prototype •http://www.lunarenergy.co.uk
Tidal Power - ENERMAR • Vertical axis Kobold turbine • Carbon fibre turbine blades • Turbine diameter 6 metres • blade span 5 metres • chord 0.4 metres • Floating platform diameter 10 metres • depth 2.5 metres • draft 1.5 metres • Mooring 4 concrete anchoring blocks
Tidal Power - ENERMAR
Messina Strait • Average tidal • 20 kW power current 2 m/s ENERMAR - output
Tidal Power: Stingray Hydroplane Device • Parallel linkage holding large hydroplanes • The angle of these hydroplanes to the flow of the tide is varied causing them to move up and down. • Motion pumps high- pressure oil in a cylinder • Hydraulic drive to an electric generator • http://www.engb.com
Tidal Power: Stingray Hydroplane Device
Measurement and prediction of tides • How do we measure tides around New Zealand? • How can we use modelling to extend the available data? • Where is the best potential for tidal power generation?
NIWA sea level network
Moturiki Is. sea level record
Tidal model of New Zealand’s EEZ
Wave energy conversion technologies • Tapered channel • Oscillating water column • Heaving buoy device • Other floating systems
Tapered Channel (TAPCHAN) A collector • concentrates incoming waves • The converter is a gradually narrowing channel in which waves increase in height • Waves overtop into a reservoir. • Hydraulic head drives flow through a turbine
The TAPCHAN at Toftestallen, Norway
Mighty Whale
Oscillating Water Column Device • Wavegen Limpet 500, Islay (Scottish west coast) • Wave capture chamber set into the rock face. • The waves cause the air in the chamber to alternately compress and decompress • Moving air drives a bidirectional Wells turbine • Presently supplying 0.5MW of power to the grid • http://www.wavegen.co.uk
Energetech OWC device • Parabolic wall focuses waves • Oscillating water Column • Dennis-Auld air turbine
Energetech OWC device - Port Kembla • Installed & tested June 2005 • Weight: 485 tonnes • 36 metres long, 35 metres wide • Will be connected to the local power grid by an 11kV cable. • Expected to produce at least 500 MWh of energy per annum. • http://www.energetech.com.au
Pendulor • Rectangular box, which is open to the sea at one end. A hinged pendulum flap swings back and forth with wave action. • Power take off through a hydraulic pump and generator. • A 15 kW prototype was tested in Muroran, Japan .
Archimedes Wave Swing • Float moves up and down relative to a fixed pontoon due to wave-induced pressure changes • Interior of the system is pressurised with air • The air spring, together with the mass of the moving part, is resonant with the frequency of the wave. • Power take off through a linear electrical generator and a nitrogen-filled damping cylinder.
Offshore device – Power Magnet Linear Generator • Works by electromagnetic induction • An electric coil fixed to the buoy, moving to a magnetic shaft anchored to the sea floor. • Each buoy could potentially produce 250 kilowatts of power • http://www.wave- energy.net/RTD/ProjDescriptions/I PS.htm
Offshore device - OPT PowerBuoy • Buoy moves up and down with the wave motion. • The resultant mechanical stroking drives the electrical generator. • The generated AC power is converted into high voltage DC and transmitted ashore via an underwater power cable. •http://www.oceanpowertechnologie s.com
Offshore device - OPT PowerBuoy
Offshore device - Pelamis • Semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. • The wave-induced motion of these joints is resisted by hydraulic rams that pump high-pressure oil through hydraulic motors. • The hydraulic motors drive electrical generators to produce electricity. • Umbilical cable to a junction on the seabed. • Several devices can be linked to shore via a single sub-sea cable. •http://www.oceanpd.com
Wave information for assessment of energy potential • How can we assess the wave climate at a given location? • How can we use modelling to extend the available data? • What variability can be expected in wave energy over various time scales? • How can we best predict wave conditions?
Datawell directional waverider buoy Accelerometers measure in x, y, z directions Integrated to give orbital velocities and x, y, z displacements Computes directional wave spectral estimates
Wave buoy data (> 1 year duration) directional non-directional
Wave buoys (present) non-directional directional
Wave statistics H T significant wave height H 1/3 = average of highest 1/3 of waves zero-crossing period T z = average of all periods
Satellite altimeter wave data A radar altimeter GEOSAT measures wave height from the spread in the return signal. Missions: SEASAT (1978) GEOSAT (1985- 1989) ERS1 & ERS2 (1991+) Topex/Poseidon (1992+)
Significant wave height from Topex/Poseidon altimeter
Wave measurement from X-band radar • WaMoS II system connected to a commercially available marine X-Band radar • Determines directional wave and surface current information from the sea clutter (up to 3 miles from the antenna )
Wave measurement from X-band radar Sea surface elevation map Radar image (sea clutter)
WAM wave generation model
New Zealand regional WAM model • spatial grid: 1.125° × 1.125° lat/lon • spectral grid 25 wave frequencies × 24 wave directions • windfields input from ECMWF reanalysis
New Zealand regional wave hindcast • A model has been established to simulate wave generation for the New Zealand region. • The model simulates deep water waves processes - wind forcing, propagation, whitecap dissipation, and nonlinear interactions. • The model has been used to hindcast 20-years (1979-1998) of deep water wave conditions at 1.125° resolution. • The hindcast has been validated against buoy and satellite data.
Hindcast: mean wave height and direction Satellite data: mean Hsig (m) 20°S 2.0 2.5 30°S 2.5 3.0 3.0 40°S 3.5 3.5 50°S 4.0 4.0 60°S
Hindcast: mean wave energy flux
Hindcast data near the coast • The hindcast is derived from a deep-water model, at relatively coarse resolution. • Most applications of hindcast data are near the coast. • The model needs to be validated against measurements, generally obtained near the coast.
Foveaux Strait buoy - 1989 Wave height from buoy and filtered WAM hindcast 8 model 7 buoy 6 Foveaux Str. buoy 5 Hsig (metres) 100 m water depth 4 3 2 1 0 21 May 10 Jun 30 Jun 20 Jul 9 Aug 29 Aug 18 Sep
Assessment of wave energy potential at Waipoua, Northland • Part of a study of renewable energy potential for remote communities • Wave energy flux was computed from WAM 20-year hindcast, for a site off the Northland coast • Work also includes wave data collection and nearshore wave refraction modelling
Wave energy flux at Waipoua Site 11 (−35.689,173.472) refracted to 30m 15 Flux Magnitude (kW/m) mean: 19.236 std. dev.: 22.531 min: 0.378 max: 514.890 % Occurrence 10 % Occurrence 5 0 0 10 20 30 40 50 60 70 80 90 100 |energy flux| (kW/m) 30m depth energy flux (kW/m)
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