(iii) Tidal power
(iv) Ocean currents
(v) Ocean winds
(vi) Salinity gradients
The first three technologies viz. wave power, OTEC and tidal power are the most developed technologies. These are briefly described below.
Wave Power :
The energy in waves comes from the movement of the ocean and the changing heights and speed of the swells. It is estimated that the total power of waves breaking on the world’s
coastlines is 2 to 3 million megawatts.
An average 4 foot, 10-second wave striking a coast puts out more than 35000 horse power per mile of coast. This is equivalent to about 65 megawatts of wave energy density per mile of coast. One of the approaches to capture wave energy is the use of oscillating water columns (OWC).
Its simple design is illustrated in The OWC generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine. The theoretical potential of renewable energy from wave energy is estimated to be on the order of 8000-80000.