Tidal Power

1. Tidal Power Low duty cycle but feasible in certain topologically favorable locations

2. Natural Tidal Bottlenecks – Its those damn crazy Welsh again … Boyle, Renewable Energy, Oxford University Press (2004)

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

4. 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 Tidal Fence Boyle, Renewable Energy, Oxford University Press (2004)

5. 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

6. Direct drive to generator No gearboxes Gravity base Versus a bored foundation Fixed pitch turbine blades Improved reliability But trades off efficiency Tidal Turbines (Swanturbines) http://www.darvill.clara.net/altenerg/tidal.htm

7. Deeper Water Current Turbine Boyle, Renewable Energy, Oxford University Press (2004)

8. Oscillates up and down 150 kW prototype operational (2003) Plans for 3 – 5 MW prototypes Oscillating Tidal Turbine http://www.engb.com Boyle, Renewable Energy, Oxford University Press (2004)

9. 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 Polo Tidal Turbine Boyle, Renewable Energy, Oxford University Press (2004)

10. 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

11. 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)

12. 2. Tidal Barrage Schemes  impound tides to create a damn resevoir

13. 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)

14. Schematic of Tidal Barrage Boyle, Renewable Energy, Oxford University Press (2004)

15. Cross Section of La Rance Barrage http://www.calpoly.edu/~cm/studpage/nsmallco/clapper.htm

16. 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 Boyle, Renewable Energy, Oxford University Press (2004) Tester et al., Sustainable Energy, MIT Press, 2005

17. La Rance Turbine Exhibit

18. La Rance River, Saint Malo

19. 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

20. La Rance Barrage Example • =33% • R = 8.5 m • A = 22 km2 GWh/yr Tester et al., Sustainable Energy, MIT Press, 2005

21. Proposed Severn Barrage (1989) Never constructed, but instructive Boyle, Renewable Energy, Oxford University Press (2004)

22. 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)

23. Severn Barrage ProposalPower Generation over Time Boyle, Renewable Energy, Oxford University Press (2004)

24. ~$15 billion (1988 costs) Severn Barrage ProposalCapital Costs So that’s about 30 Billion dollars today for 9 Billion Watts  not terrible but not great Boyle, Renewable Energy, Oxford University Press (2004) Tester et al., Sustainable Energy, MIT Press, 2005

25. 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

26. 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

27. 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

28. But Bottom Line Sum is only about 70 GW  BFD? Promising Tidal Energy Sites http://europa.eu.int/comm/energy_transport/atlas/htmlu/tidalsites.html

29. 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)