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

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

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.

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,

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.

Wells turbine.

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,

Wells turbine.

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

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

Other types :

Tidal Power Tidal power stations take advantage of the tidal rise and fall to generate electricity. http://www.ipe.cuhk.edu.hk/

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

Tidal current power device

Cross section of a typical tidal barrage

M´eriadec mill, Badens

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.

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

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

Imaginary of OTEC Plant in Islands Country