Tidal%20Power

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Tidal Power

• Low duty cycle but feasible in certain
  topologically favorable locations

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Natural Tidal Bottlenecks - Wales
Boyle, Renewable Energy, Oxford University Press
(2004)
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In Nova Scotia
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1. Tidal Turbine Farms Challenge its to optimize
turbine design
300 KW Turbine
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State of the Art Design
1.5 MW 1350 Tons
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Tidal Fence

• Array of vertical axis tidal turbines
• No effect on tide levels
• Less environmental impact than a barrage
• 1000 MW peak (600 MW average) fences soon

Boyle, Renewable Energy, Oxford University Press
(2004)
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Tidal Turbines (MCT Seagen)

• 750 kW 1.5 MW
• 15 20 m rotors
• 3 m high Pile
• 10 20 RPM
• Deployed in multi-unit farms or arrays
• Like a wind farm, but
• Water 800x denser than air
• Smaller rotors
• More closely spaced

MCT Seagen Pile
http//www.marineturbines.com/technical.htm
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Tidal Turbines (Swanturbines)

• Direct drive to generator
• No gearboxes
• Gravity base
• Versus a bored foundation
• Fixed pitch turbine blades
• Improved reliability
• But trades off efficiency

http//www.darvill.clara.net/altenerg/tidal.htm
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Deeper Water Current Turbine
Boyle, Renewable Energy, Oxford University Press
(2004)
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Oscillating Tidal Turbine

• Oscillates up and down
• 150 kW prototype operational (2003)
• Plans for 3 5 MW prototypes

http//www.engb.com
Boyle, Renewable Energy, Oxford University Press
(2004)
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Polo Tidal Turbine

• Vertical turbine blades
• Rotates under a tethered ring
• 50 m in diameter
• 20 m deep
• 600 tonnes
• Max power 12 MW
• Much better power per ton ratio than Power Buoys

Boyle, Renewable Energy, Oxford University Press
(2004)
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Advantages of Tidal Turbines

• Low Visual Impact
• Mainly, if not totally submerged.
• Low Noise Pollution
• Sound levels transmitted are very low
• High Predictability
• Tides predicted years in advance, unlike wind
• High Power Density
• Much smaller turbines than wind turbines for the
  same power

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Disadvantages of Tidal Turbines

• High maintenance costs
• High power distribution costs
• Somewhat limited upside capacity ? less than 100
  GW worldwide
• Intermittent power generation over 24 hour day
• Fish bumping (but not chopping due to low RPM)

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2. Tidal Barrage Schemes ? impound tides to
create a damn resevoir
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Potential Tidal Barrage Sites
Only about 20 sites in the world have been
identified as possible tidal barrage stations
Boyle, Renewable Energy, Oxford University Press
(2004)
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Schematic of Tidal Barrage
Boyle, Renewable Energy, Oxford University Press
(2004)
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Cross Section of La Rance Barrage
http//www.calpoly.edu/cm/studpage/nsmallco/clapp
er.htm
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La Rance Tidal Power Barrage

• Rance River estuary, Brittany (France)
• Largest in world 750 m dike
• Completed in 1966
• 2410 MW bulb turbines (240 MW)
• 5.4 meter diameter
• Capacity factor of 33
• Electric cost 3.7/kWh

Tester et al., Sustainable Energy, MIT Press, 2005
Boyle, Renewable Energy, Oxford University Press
(2004)
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La Rance Turbine Exhibit
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La Rance River, Saint Malo
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Tidal Barrage Energy Calculations

• R range (height) of tide (in m)
• A area of tidal pool (in km2)
• m mass of water
• g 9.81 m/s2 gravitational constant
• 1025 kg/m3 density of seawater
• ? 0.33 capacity factor (20-35)

kWh per tidal cycle
Assuming 706 tidal cycles per year (12 hrs 24 min
per cycle)
Tester et al., Sustainable Energy, MIT Press, 2005
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La Rance Barrage Example

• 33
• R 8.5 m
• A 22 km2

GWh/yr
Tester et al., Sustainable Energy, MIT Press, 2005
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Proposed Severn Barrage (1989)
Never constructed, but instructive
Boyle, Renewable Energy, Oxford University Press
(2004)
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Proposed Severn Barrage (1989) ? Impressive Scale

• Severn River estuary (Border between Wales and
  England)
• 216 40 MW turbine generators (9.0m dia)
• 8,640 MW total capacity
• 16 km (9.6 mi) total barrage length
• 8.2 (15) billion estimated cost (1988)

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Severn Barrage ProposalCapital Costs
Boyle, Renewable Energy, Oxford University Press
(2004)
Tester et al., Sustainable Energy, MIT Press, 2005
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Tidal Barrage Environmental Factors

• Changes in estuary ecosystems
• Less variation in tidal range
• Fewer mud flats
• Less turbidity clearer water
• More light, more life
• Accumulation of silt
• Concentration of pollution in silt
• Visual clutter

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Advantages of Tidal Barrages

• High predictability
• Tides predicted years in advance, unlike wind
• Similar to low-head dams
• Known technology
• Protection against floods
• Benefits for transportation (bridge)
• Some environmental benefits

http//ee4.swan.ac.uk/egormeja/index.htm
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Disadvantages of Tidal Barrages

• High capital costs
• Few attractive tidal power sites worldwide
• Intermittent power generation
• Silt accumulation behind barrage
• Accumulation of pollutants in mud
• Changes to estuary ecosystem

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Promising Tidal Energy Sites
But Bottom Line Sum is only about 70 GW ? BFD?


Country Location TWh/yr GW
Canada Fundy Bay 17 4.3
  Cumberland 4 1.1
USA Alaska 6.5 2.3
  Passamaquody 2.1 1
Argentina San Jose Gulf 9.5 5
Russia Orkhotsk Sea 125 44
India Camby 15 7.6
  Kutch 1.6 0.6
Korea   10  
Australia   5.7 1.9
http//europa.eu.int/comm/energy_transport/atlas/h
tmlu/tidalsites.html
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Local Sites

• Tacoma Narrows
• Deception Pass (Oceana Energy has Permit)
• San Francisco Bay (Golden Gate)
• Straits of Juan De Fuca (twice the scale to that
  of Severn Barge)