Tidal Power

This form of energy derives directly from the relative moves of Earth, Moon and Sun.

Tidal power is classified as a renewable energy source because it’s generated by the gravity interactions between Earth, Moon and Sun.

The Earth-Moon system is losing mechanical energy because of the tides. Because of this loss of energy, in the last 620 million years the rotation period of Earth has increased from 22 to 24 hours.

Tidal power can be converted into electricity using:

- Tidal stream generators;

- Barrages.

Tidal Stream Generators

This technology transforms the energy from the currents (kinetic energy) like the wind turbines do.

Now you’re probably thinking: ‘But the speed of water is around one-tenth of the wind speed!’ Yes, that’s true. But the water density is around 830 times the density of air, so a system of turbine of the same size may produce the same power.

Barrage Tidal Power

Barrages, placed into estuaries, use the difference of height (potential energy) between low and high tides.
This way to produce electricity involves more costs, can only be used in some sites and may cause some environmental issues. Those environmental issues are related to the reduction of the saltwater flow, what make changes to the estuary as a habitat.





Sources:
http://en.wikipedia.org/wiki/Tidal_power
http://www.youtube.com/watch?v=tSBACzRE3Gw