Wave and Tidal Energy Richard Gorman National Institute of Water - - PowerPoint PPT Presentation

Wave and Tidal Energy

Richard Gorman

National Institute of Water and Atmospheric Research Maori and the Sustainable Energy Business – 3-4 August 2005, Taupo

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
• f 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 technologies

• Tidal barrage
• Underwater turbines
• Hydroplane devices

• Rance Estuary, Brittany, France
• Construction began in 1960,

completed in 1967

• Dam length 330 m
• 22 km2 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

Rance Estuary Tidal Barrage

Tidal Power – SeaFlow turbine

• Marine Current

Turbines Ltd (UK)

• Pilot plant installation in

the Bristol Channel

• horizontal axis turbine
• http://www.mct.com

• 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 : Rotech Turbine

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

ENERMAR - Messina Strait

• Average tidal

current 2 m/s

• 20 kW power
• utput

• 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

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
• f 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
• ne 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.

• 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 – Power Magnet Linear Generator

• 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 - OPT PowerBuoy

• 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

Offshore device - Pelamis

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?

Accelerometers measure in x, y, z directions Integrated to give orbital velocities and x, y, z displacements Computes directional wave spectral estimates

Datawell directional waverider buoy

directional non-directional

Wave buoy data (> 1 year duration)

directional non-directional

Wave buoys (present)

H T significant wave height H1/3 = average of highest 1/3 of waves zero-crossing period Tz = average of all periods

Wave statistics

Satellite altimeter wave data

GEOSAT A radar altimeter 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

Radar image (sea clutter) Sea surface elevation map

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)

2.0 2.5 2.5 3.0 3.0 3.5 3.5 4.0 4.0

20°S 30°S 40°S 50°S 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

• btained near the coast.

Foveaux Strait buoy - 1989

21 May 10 Jun 30 Jun 20 Jul 9 Aug 29 Aug 18 Sep 1 2 3 4 5 6 7 8 model buoy

Wave height from buoy and filtered WAM hindcast Hsig (metres)

Foveaux Str. buoy 100 m water depth

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

10 20 30 40 50 60 70 80 90 100 5 10 15 |energy flux| (kW/m) 30m depth % Occurrence Flux Magnitude (kW/m) mean: 19.236

• std. dev.: 22.531

min: 0.378 max: 514.890 Site 11 (−35.689,173.472) refracted to 30m

energy flux (kW/m) % Occurrence

Wave energy flux at Waipoua

1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 10 20 30 40 50 60

monthly mean |Flux| (kW/m) Site 11 (−35.689,173.472) refracted to 30m

monthly mean energy flux (kW/m) year

Monthly mean wave energy flux at Waipoua

1 2 3 4 5 6 7 8 9 10 11 12 10 20 30 40 50 60 70

Month monthly mean |Flux| (kW/m) Site 11 (−35.689,173.472) refracted to 30m

Wave energy flux mean annual cycle

New Zealand regional wave forecast

http://www.niwa.co.nz/ncco/forecast/

Wave forecast - Otago

• Some wave energy

devices can be “tuned” or secured depending on wave conditions

• Can use ocean scale

forecasts to predict wave conditions hours/days ahead

• It may be possible to

combine measurement and models to predict on a wave-by-wave basis seconds/minutes ahead

Wave prediction

Summary

• Tidal and wave energy are relatively

concentrated forms of renewable energy

• Tidal motions are very predictable and reliable
• Wave conditions are more variable in time, but

still predictable

• New Zealand has some favourable locations for

both tidal and wave energy generation

• Technologies are developing

North Island tidal currents

Moturiki Is. long wave record

Tidal model validation

M2 Tidal ellipses from the EEZ model (red) and current meter deployments (blue)

Tidal model of New Zealand’s EEZ

Cook Strait tidal currents

Banks Peninsula tidal currents

Foveaux Strait tidal currents

Oscillating Water Column Device

H T significant wave height H1/3 = average of highest 1/3 of waves zero-crossing period Tz = average of all periods

Wave statistics

= + + + + ...

) (t z

.... cos cos cos cos + + + + = t a t a t a t a

4 4 3 3 2 2 1 1

ω ω ω ω

Each component travels with a different speed

Wave components

Directional wave spectrum

fpeak fpeak

T = 2 1 0.66 0.5 seconds

Wave measurement - summary

• Wave time series at one point – wave

staffs, wave buoys, current meters, pressure sensors

• Remote sensing – satellite, radar, lidar
• From point records, compute summary

statistics, e.g. significant wave height

• Represent the sea state by a spectrum,

describing the energy carried at different wave frequencies and propagation directions