“Other Energy”

1. “Other Energy” Professor Ian Bryden Chair of Renewable Energy

2. Contents • Tidal Barrages • Ocean Thermal Energy Conversion (OTEC) • Geothermal Energy

3. Tidal Barrages • Principles • La Rance • Ebb Generation • Flood Generation • Environmental Issues • Lagoons

4. Tidal Barrage Systems • Essentially modern electrical generation developments of the traditional tidemill • In the nineteenth and twentieth centuries, there were numerous proposals to exploit the tidal energy potential of the Severn Estuary. None have yet been developed. • The world's first serious scheme to exploit tidal energy was constructed in France, at La Rance in Brittany, between 1961 and 1967 and consists of a barrage across a tidal estuary to utilise the rise and fall in sea level induced by the tides.

5. Tidal Barrage Systems • Designed to harness the rise and fall of the sea by enclosing tidal estuaries eg • LaRance, Severn, Solway

6. LaRance • The world’s first serious scheme to exploit tidal energy was constructed in France, at La Rance in Brittany, between 1961 and 1967. • It consists of a barrage across a tidal estuary to utilise the rise and fall in sea level induced by the tides. • This scheme has proven itself to be highly successful despite some early teething problems.

7. La Rance Tidal Barrage Now 36 years old! Currently undergoing a 10 year maintenance programme

8. Cross Section of a Tidal Barrage http://europa.eu.int/comm/energy_transport/atlas/htmlu/tidal.html

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

10. Tidal Barrage Rim Generator Boyle, Renewable Energy, Oxford University Press (2004)

11. Tidal Barrage Tubular Turbine Boyle, Renewable Energy, Oxford University Press (2004)

12. La Rance Tidal Power Barrage • Rance River estuary, Brittany (France) • Largest in world • Completed in 1966 • 24×10 MW bulb turbines (240 MW) • 5.4 meter diameter • Capacity factor of ~40% • 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

13. La Rance Tidal Power Barrage http://www.stacey.peak-media.co.uk/Brittany2003/Rance/Rance.htm

14. La Rance River, Saint Malo

15. La Rance Barrage Schematic Boyle, Renewable Energy, Oxford University Press (2004)

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

17. La Rance Turbine Exhibit

18. 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

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

20. Possible Sites World Wide

21. Ebb Generation • This is the most likely approach to be used commercially • Sluices are opened during the flood tide allowing the basin to fill up. • Sluices are closed at high tide and during the ebb tide a head is initially allowed to develop • Once a sufficient head has been developed between the basin and the outer waters, gates are opened and water allowed to flow out of the basin through turbines.

22. Flood Tide- Sea water flows through sluices into basin Open sea Within barrage flow of water through sluices

23. High Tide- Sluices closed to retain water in basin Open sea Within barrage flow of waer through sluices

24. Ebb Tide(a)- water retained in the basin to allow a useful head to develop Open sea Within barrage

25. Ebb Tide(b)- sea water flowing through generators Open sea Within barrage flow of water through turbines

26. Ebb Generation

27. Flood Generation Mode • In this alternative to ebb generation, the sluices are are closed at low water and a head develops during the flood tide. • Gates are opened once the head is sufficient to drive the turbines.

28. Flood Generation

29. Two Basin Systems • Double basin system have been proposed to allow an element of storage and to give time control over power output levels. • Typically, he main basin would behave, essentially like an ebb generation single basin system. • A proportion of the electricity generated during the ebb phase would be used to pump water to and from the second basin to ensure that there would always by a generation capability.

30. Multiple basin systems are unlikely to become popular, as the efficiency of low-head turbines is likely to be too low to enable effective economic storage of energy. • The overall efficiency of such low head storage, in terms of energy out and energy in, is unlikely to exceed 30%. • It is more likely that conventional pump-storage systems will be utilised. • The overall efficiencies of these systems can exceed 70% which is, especially considering that this is a proven technology, likely to prove more financially attractive.

31. Two Basin Systems

32. Combined Generation and Storage

33. The Financial Implications of Tidal Barrage Development • Severn Estuary could provide in excess of 8 % of the UK’s requirement for electrical energy . • La Rance took 6 years to complete. No electricity could be generated before the total project was completed. This is a major disincentive for commercial investment.

34. Environmental Opposition to Tidal Barrages • Environmental groups, although generally in favour of the exploitation of alternative energy sources, are suspicious of the likely environmental changes large estuary based schemes would produce. • One politician in the UK likened the proposed creation of a barrage across the Severn Estuary to the formation of a “large stinking lake”. • Similar opposition has been voiced against any development of the tidal resource in the Solway Firth between Scotland and England. It is anticipated that public and political opposition will limit the development of tidal barrage schemes in the short term.

35. An ebb generation system will reduce the time tidal sands are uncovered. This would have considerable influences on the lives of wading birds and other creatures. • The presence of a barrage will also influence maritime traffic and it will always be necessary to include locks to allow vessels to pass through the barrage. • This problem will be less problematic for an ebb system, where the basin is potentially kept at a higher level, than it would be with a flood generation system, in which the basin would be kept at a lower than natural level.

36. Offshore Tidal Lagoon Boyle, Renewable Energy, Oxford University Press (2004)

37. Ocean Thermal Energy Conversion (OTEC) • Principles • Closed Cycle • Open Cycle • Hybrid systems • Applications

38. Ocean Thermal Energy Conversion (OTEC) • Ocean Thermal Energy Conversion produces electricity from the natural thermal gradient of the ocean, using the heat stored in warm surface water to create steam to drive a turbine, while pumping cold, deep water to the surface to recondense the steam.

39. Global Ocean Thermal Gradient Temperature difference between warm surface water and cold deep water must be >20°C (36°F) for OTEC system to produce significant power

40. Ocean Thermal Energy Conversion • Ocean Thermal Energy Conversion is only viable in the tropical seas, in areas where the thermal gradient between the surface and a depth of 1000m is at least 22°C.

41. Ocean Thermal Energy Conversion (OTEC) • Generates power with temperature differential between warm surface water and cooler, deep water • Requires temp differential of 36 F • 50 kW mini-OTEC plant in Hawaii operated in the ’80s • OTEC limited applications • Very costly • Limited suitable sites • can’t justify for electricity – must also desalinize, sustain aquaculture, etc…

42. The Technologies: Ocean Thermal Energy Conversion (OTEC) • Ocean’s natural thermal gradient (warm surface waters, cold deep waters) drives power-producing cycle • OTEC converts solar radiation to electric power • Tropical seas cover 60 million km2 -- world’s largest solar collector • Solar radiation absorbed on average day equal in heat content to ~250 billion barrels of oil • Three types of OTEC systems: open, closed, and hybrid

43. Ocean Thermal Energy Conversion

44. Closed Cycle OTEC • In closed-cycle OTEC, warm seawater heats a working fluid, such as ammonia, with a low boiling point, such as ammonia, which flows through a heat exchanger (evaporator). • The ammonia vapor expands at moderate pressures turning a turbine, which drives a generator which produces energy. • The vapor is then condensed in another heat exchanger (condenser) by the cold, deep-ocean water running through a cold water pipe. • The working fluid (ammonia) is then cycled back through the system, being continuously recycled.

45. OTEC Open CycleSystem • In an open-cycle plant, the warm water, after being vaporized, can be recondensed and separated from the cold seawater, leaving behind the salt and providing a source of desalinated water fresh enough for municipal or agricultural use.

46. Open Cycle OTEC • In an open-cycle OTEC plant, warm seawater from the surface is the working fluid that is pumped into a vacuum chamber where it is flash- evaporated to produce steam at an absolute pressure of about 2.4 kilopascals (kPa). • The resulting steam expands through a low-pressure turbine that is hooked up to a generator to produce electricity. • The steam that exits the turbine is condensed by cold, deep-ocean water, which is returned to the environment. • If a surface condenser is used, the condensed steam remains separated from the cold ocean water and can be collected as a ready source of desalinated water for commercial, domestic or agricultural use.

47. OTEC Hybrid Cycle System Hybrid plants, combining benefits of the two systems, would use closed-cycle generation combined with a second-stage flash evaporator to desalinate water.

48. Case Study:: Cayman Trench • For a shore-based plant, an additional requirement is topography that allows access to very deep water (1km or deeper) directly offshore, conditions that exist at certain tropical islands, coral atolls, and a limited number of continental sites. • In the United States, potential sites include Hawaii, Puerto Rico, and the continental shelf off the Gulf of Mexico. • The three Cayman Islands are an ideal location for OTEC technology, as they are surrounded by the Cayman Trough to the north and the Bartlett Deep to the south. This is the deepest part of the Caribbean, over four miles deep. • Islands off of the Puerto Rican trench are also viable locations.

49. Potential OTEC Sites • The OTEC platforms could be located in shallow water, right on the edge of the trench, which is a huge escarpment like structure that plunges straight down. • The South Pacific and Molokai, Hawaii. • American Territories such as Guam, American Samoa and US Gulf Coastal areas. • Hawaii. • Caribbean islands adjacent to deep-sea trenches. • Puerto Rico, Gulf of Mexico, Pacific, Atlantic and Indian Oceans. • Military and security uses of large floating plant -ships with major life-support systems such as power, desalinated water, cooling and aquatic food. Ships such as this would have saved many lives and relieved great suffering in disaster areas such as Banda Ache, Thailand, Indonesia, Sri Lanka and the US Gulf Coast.

50. OTEC Efficiency • The thermal gradient gives OTEC a typical energy conversion of 3 to 4%, whereas conventional oil or coal fired steam plants, often have temperature differentials of 500oF, yielding thermal efficiencies of 30 to 35%. • Remember, the greater the difference between hot and cold temperatures, the greater the efficiency of the energy conversion system. • So to compensate for its low thermal efficiency, OTEC has to move a tremendous amount of water. • It takes 20 to 40% of the power generated to pump the water through intake pipes in and around an OTEC system. • This is why, almost 100 years after the idea was first conceive, OTEC researchers are still striving to develop plants that will consistently produce more energy than is needed to run the pumps, and that will operate in the corrosive marine climate, to justify the development and construction.