Tidal Power

Low duty cycle but feasible in certain topologically favorable locations 1

Natural Tidal Bottlenecks – Its those damn crazy Welsh again …

2 Boyle,

Renewable Energy,

Oxford University Press (2004)

1. Tidal Turbine Farms: Challenge its top optimize turbine design

3

Boyle,

Renewable Energy,

Oxford University Press (2004)

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 4

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

5

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 6 http://www.darvill.clara.net/altenerg/tidal.htm

Deeper Water Current Turbine

Boyle,

Renewable Energy,

Oxford University Press (2004) 7

Oscillating Tidal Turbine

   Oscillates up and down 150 kW prototype operational (2003) Plans for 3 – 5 MW prototypes http://www.engb.com

8 Boyle,

Renewable Energy,

Oxford University Press (2004)

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 9 Boyle,

Renewable Energy,

Oxford University Press (2004)

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 10

Disadvantages of Tidal Turbines

 High maintenance costs   High power distribution costs Somewhat limited upside capacity  100 GW worldwide less than  Intermittent power generation over 24 hour day  Fish bumping (but not chopping due to low RPM) 11

2. Tidal Barrage Schemes



impound tides to create a damn resevoir

12

Potential Tidal Barrage Sites

Only about 20 sites in the world have been identified as possible tidal barrage stations 13 Boyle,

Renewable Energy,

Oxford University Press (2004)

Schematic of Tidal Barrage

Boyle,

Renewable Energy,

Oxford University Press (2004) 14

Cross Section of La Rance Barrage

http://www.calpoly.edu/~cm/studpage/nsmallco/clapper.htm

15

La Rance Tidal Power Barrage

 Rance River estuary, Brittany (France)  Largest in world – 750 m dike   Completed in 1966 24 × 10 MW bulb turbines (240 MW)  5.4 meter diameter  Capacity factor of ~33 %  Maximum annual energy: 2.1 TWh  Realized annual energy: 840 GWh  Electric cost: 3.7¢/kWh 16 Tester

et al., Sustainable Energy,

MIT Press, 2005 Boyle,

Renewable Energy,

Oxford University Press (2004)

La Rance Turbine Exhibit

17

La Rance River, Saint Malo

18

Tidal Barrage Energy Calculations

E R =

range (height) of tide (in m) A = area of tidal pool (in km 2 )

m

= mass of water

g

=  =  

9.81 m/s 2 1025 kg/m

= gravitational constant

3

= density of seawater 0.33 = capacity factor (20-35%)  

mgR

/ 2   ( 

AR

)

gR

/ 2

E

 1397 

R

2

A

kWh per tidal cycle Assuming 706 tidal cycles per year (12 hrs 24 min per cycle)

E yr

 0 .

997  10 6 

R

2

A

Tester

et al., Sustainable Energy,

MIT Press, 2005 19

La Rance Barrage Example  = 33%

R

= 8.5 m A = 22 km 2

E yr

 0 .

997  10 6 

R

2

A E yr

 0 .

997  10 6

E yr

 517 ( 0 .

33 )( 8 .

5 2 )( 22 ) GWh/yr Tester

et al., Sustainable Energy,

MIT Press, 2005 20

Proposed Severn Barrage (1989) Never constructed, but instructive Boyle,

Renewable Energy,

Oxford University Press (2004) 21

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) 22

Severn Barrage Proposal Power Generation over Time

Boyle,

Renewable Energy,

Oxford University Press (2004) 23

Severn Barrage Proposal Capital Costs

~$15 billion (1988 costs) 24 Boyle,

Renewable Energy,

Oxford University Press (2004)

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 25

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

26

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 27

But Bottom Line Sum is only about 70 GW



BFD?

Promising Tidal Energy Sites Country Canada USA Argentina Russia India Location

Fundy Bay Cumberland Alaska Passamaquody San Jose Gulf Orkhotsk Sea Camby Kutch

Korea Australia

http://europa.eu.int/comm/energy_transport/atlas/htmlu/tidalsites.html

TWh/yr

17 4 6.5

2.1

9.5

125 15 1.6

10 5.7

GW

4.3

1.1

2.3

1 5 44 7.6

0.6

1.9

28

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) 29