1. ERT353: Ocean energy April 2014
Principle and devices of :
Wave power :
Tidal power
Ocean thermal energy conversion (OTEC

2. electricity generation, water desalination, or the pumping of water
WAVE POWER
Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example for
electricity generation, water desalination, or the pumping of water

3. Was used in California in 1909 for harbour lighting
Difficulties facing wave power
Irregularity in wave patterns, amplitude, phase and direction > difficult to design devices
probability of extreme gales or hurricanes
Peak power is generally available in deep water → difficult for transmitting power to land
Wave periods are commonly ∼5–10 s (frequency ∼01Hz). --> difficult to couple this irregular slow motion to electrical generators requiring ∼500 times greater frequency.

4. Example 1: Wave capture systems
Waves break over a sea wall and water is impounded at a height above the mean sea level. This water may then return to the sea through a conventional low head hydroelectric generator,

5. Waves flow over the top of the tapered channel into the
reservoir. Water flows from the pipe P near the top of the reservoir, though hydro turbines and then out to the sea at Q.

6. Wells turbine.

7. Example 2: Oscillating water column (OWC)
Electrical power is derived from the oscillating airstream using a Wells turbine; once started, turn in the same direction to extract power from air flowing in either axial direction,

8. Wells turbine.

9. Wave profile devices
This class of devices float on the sea surface and move in response to the shape of the wave, rather than just the vertical displacement of water.
Ingenious design is needed to extract useable power from the motion

10. Sketch of the Pelamis wave-power device, as seen from the side
Sketch of the Pelamis wave-power device, as seen from the side . Motion at the hinges produces hydraulic
power fed to electrical generators
Pelamis

11. Other types :

12. Tidal Power
Tidal power stations take advantage of the tidal rise and fall to generate electricity.

13. The major drawbacks are: 1 Optimum tidal is difficult to predict .
2 The change of tidal range over a two-week period, producing changing power production.
3 The requirement for large water volume flow--> need specially constructed turbines set in parallel.
4 The very large capital costs of most potential installations.
Tidal anim

16. Tidal current power device

17. Cross section of a typical tidal barrage

19. M´eriadec mill, Badens

20. Prototype of a tidal turbine installed o the Coast of Devon, England
Prototype of a tidal turbine installed o the Coast of Devon, England. The rotor/turbine assembly is shown in the raised position for maintenance.

22. Ocean Thermal Energy Conversion (OTEC)
Uses the temperature difference between deep and shallow waters to run a heat engine.
The greatest efficiency and power is produced with the largest temperature difference.
This temperature difference generally increases with decreasing latitude, i.e. near the equator, in the tropics.
Performance can be improved by improving efficiency of heat exchange in modern designs

26. At a temperature of 15 C, the pressure inside the canister is about 15
kPa (0.017 atmospheres). At this pressure, warm water at 25 C will boil
and the resulting vapor will condense on the parts of the dome refrigerated
by the cold water. The condensate runs o into the ocean, establishing a
continuous ow of warm water into the canister

28. Imaginary of OTEC Plant in Islands Country