Electricity Production from Renewables Energies

4.2. Hydraulic power of the sea

4.2.1. Wave power

4.2.1.1. Origin and description of the waves

Waves are a form of non-polluting renewable energy. They can be created by:

– the presence of an object in water (example: wake of a boat);

– the crossing of currents;

– seismic and volcanic activity;

– wind blowing at the surface of water.

In this book, we will take a more specific look at waves generated by the wind, because their energy concentration is the highest in comparison to other waves. They represent a natural conversion of the wind power coming from wind blowing on the ocean surfaces, which itself coming from the conversion of part of the solar power. With these two successive conversions, energy is very concentrated. The average flow of the wave power is generally five times denser in surface waters than that of the wind power located 20 m above the sea surface and 10 to 30 times denser than the solar power flow.

When the wind blows on a smooth surface of water, air particles rub water molecules. This frictional force between air and water, associated with the surface tension of water and with gravity, spreads over the surface, thereby forming small wrinkles or oscillations. The latter are called capillary waves. They will become increasingly well formed as the wind keeps on blowing. The size of the waves depends on the wind speed, on the distance over which it blows – called the fetch – on the time during which the wind blows, as well as on the depth and the topography ...