ABSTRACT
The level of water in oceans rises and falls predictably as tides due to the relative positions of the Sun, Earth and Moon. Since the astronomical periodicities are known accurately and the effects of particular coastlines remain constant, the prediction of tidal rhythms and amplitudes is mathematically exact. The main periods t of tides are diurnal at about 24 hours and semi-diurnal at about 12 hours 25 minutes. The change in height between successive high and low tides is the tidal range, R. This varies between about 0.6 m in mid-ocean to about 10 m at a few locations of continental land masses. The movement of the water produces periodic tidal currents, which may reach peak speeds of ~5 m/s in coastal and inter-island channels. The increased tidal flow and tidal range at specific locations permit two distinct technologies for electricity generation, namely (a) tidal-current power (also called tidal-stream power), and (b) tidal-range power. We consider both technologies in this chapter, despite their considerable differences.
