Tidal
Tidal power, also known as tidal energy, is a form of hydropower that exploits the movement of water caused by tidal currents or the rise and fall in sea levels due to the tides.
Although not yet widely used, tidal power has potential for future electricity generation and is more predictable than wind energy and solar power. In Europe, tide mills have been used for many centuries mainly for grinding grains.
This is the only form of energy which comes from the tidal forces by the Moon and the rotation of the Earth in the Earth-Moon system, though some of it comes from the solar tidal forcing as well. Most other sources of energy originate directly or indirectly from the Sun, including fossil fuels, conventional hydroelectric, wind, biofuels, and solar. The remainder, nuclear and geothermal for instance, have radioactive material on Earth as their source.
Tidal energy is generated by the relative motion of the Earth, Sun and the Moon, which interact via gravitational forces. Due to the interaction of these gravitational forces with the water in the oceans and seas, in combination with the Earth’s rotation, water levels follow periodic highs and lows. Associated with these water level changes, there are tidal currents. The specific tidal motion produced at a certain location is the result of the changing positions of the Moon and Sun relative to the Earth, the effects of Earth rotation, and the local shape of the sea floor and coastlines.
A tidal energy generator uses this phenomenon to generate energy. The stronger the tide, either in water level height or tidal current velocities, the greater the potential for tidal energy generation.
Tidal movement causes a continual loss of energy in the Earth-Moon system due to pumping of water through the natural restrictions around coastlines. This loss of energy has caused the period of rotation of the earth to slow in the 4.5 billion years since formation from perhaps 17hrs to 24hrs we see now. There is less than half the rotational energy in the system now than at formation. Tidal power takes further energy from the system, increasing the rate of slowing.
