Tidal Power
Low duty cycle but feasible in certain
topologically favorable locations
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Natural Tidal Bottlenecks – Its those
damn crazy Welsh again …
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Boyle, Renewable Energy, Oxford University Press (2004)
1. Tidal Turbine Farms:
Challenge its top
optimize turbine design
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Tidal Fence
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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
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Boyle, Renewable Energy, Oxford University Press (2004)
Tidal Turbines (MCT Seagen)
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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
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Water 800x denser than air
Smaller rotors
More closely spaced
MCT Seagen Pile
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http://www.marineturbines.com/technical.htm
Tidal Turbines (Swanturbines)
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Direct drive to generator
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Gravity base
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Versus a bored foundation
Fixed pitch turbine blades
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http://www.darvill.clara.net/altenerg/tidal.htm
No gearboxes
Improved reliability
But trades off efficiency
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Deeper Water Current Turbine
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Boyle, Renewable Energy, Oxford University Press (2004)
Oscillating Tidal Turbine
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Oscillates up and down
150 kW prototype
operational (2003)
Plans for 3 – 5 MW
prototypes
http://www.engb.com
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Boyle, Renewable Energy, Oxford University Press (2004)
Polo Tidal Turbine
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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
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Boyle, Renewable Energy, Oxford University Press (2004)
Advantages of Tidal Turbines
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Low Visual Impact
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Low Noise Pollution
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Sound levels transmitted are very low
High Predictability
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Mainly, if not totally submerged.
Tides predicted years in advance, unlike wind
High Power Density
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Much smaller turbines than wind turbines for the
same power
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Disadvantages of Tidal Turbines
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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
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Boyle, Renewable Energy, Oxford University Press (2004)
Schematic of Tidal Barrage
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Boyle, Renewable Energy, Oxford University Press (2004)
Cross Section of La Rance
Barrage
http://www.calpoly.edu/~cm/studpage/nsmallco/clapper.htm
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La Rance Tidal Power Barrage
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Rance River estuary, Brittany (France)
Largest in world – 750 m dike
Completed in 1966
24×10 MW bulb turbines (240 MW)
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5.4 meter diameter
Capacity factor of ~33 %
Maximum annual energy: 2.1 TWh
Realized annual energy: 840 GWh
Electric cost: 3.7¢/kWh
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Boyle, Renewable Energy, Oxford University Press (2004)
Tester et al., Sustainable Energy, MIT Press, 2005
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%)
E  mgR/ 2   ( AR) gR / 2
E  1397R A kWh per tidal cycle
2
Assuming 706 tidal cycles per year (12 hrs 24 min per cycle)
Eyr  0.99710 R A
6
2
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Tester et al., Sustainable Energy, MIT Press, 2005
La Rance Barrage Example
 = 33%
R = 8.5 m
A = 22 km2
E yr  0.997106R 2 A
E yr  0.99710 (0.33)(8.5 )(22)
6
2
E yr  517 GWh/yr
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Tester et al., Sustainable Energy, MIT Press, 2005
Proposed Severn Barrage (1989)
Never constructed, but instructive
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Boyle, Renewable Energy, Oxford University Press (2004)
Proposed Severn Barrage (1989) 
Impressive Scale
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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 Proposal
Power Generation over Time
23
Boyle, Renewable Energy, Oxford University Press (2004)
Severn Barrage Proposal
Capital Costs
~$15 billion
(1988 costs)
24
Boyle, Renewable
Tester
et al., Sustainable
Energy,Energy,
OxfordMIT
University
Press, Press
2005 (2004)
Tidal Barrage Environmental
Factors
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Changes in estuary ecosystems
Less variation in tidal range
 Fewer mud flats
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Less turbidity – clearer water
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Accumulation of silt
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More light, more life
Concentration of pollution in silt
Visual clutter
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Advantages of Tidal Barrages
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High predictability
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Similar to low-head dams
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Tides predicted years in advance, unlike wind
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
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High capital costs
Few attractive tidal power sites worldwide
Intermittent power generation
Silt accumulation behind barrage
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Accumulation of pollutants in mud
Changes to estuary ecosystem
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But Bottom Line Sum is only about 70 GW  BFD?
Promising Tidal Energy Sites
Country
Location
TWh/yr
GW
Canada
Fundy Bay
17
4.3
Cumberland
4
1.1
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
USA
Korea
10
Australia
5.7
http://europa.eu.int/comm/energy_transport/atlas/htmlu/tidalsites.html
1.9
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Local Sites
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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)
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