Tidal power
Tidal power is a means of electrical generation that uses the difference in height (or head) between high and low tides. It is one of a number of forms of water power. Because tides are caused by the orbital mechanics of the solar system, they are considered inexhaustible within a human timeframe. Tidal generation has great potential for future power and electricity generation because of the total amount of energy involved in the process. Tidal power is reliably predictable (unlike wind energy and solar power) and renewable, tapping the virtually infinite amount of the earth's rotational energy.The efficiency of tidal power generation largely depends on the amplitude of the tidal swell, which can be up to 10m (33 feet) where the periodic tidal waves funnel into rivers and fiords. Amplitudes of up to 17m (56 feet) occur for example in the Bay of Fundy, where tidal resonance amplifies the tidal waves.
Several smaller tidal power plants have recently started generating electricity in Norway. They all exploit the strong periodic tidal currents in narrow fiords using sub-surface propellers.