What is Tidal Power?
What is tidal power ? Well, the simple answer is that it is energy harnessed from ocean tides. Anywhere you have kinetic energy, which is to say energy that moves an object from one place to another you can harness that energy to move a turbine. The turbine is attached to a generator and that makes electricity. Because the tides move water, that movement can be used to spin a turbine. It really is that simple in concept. Of course, implementation is a bit more difficult thanks to some of the aspects mentioned above.
A tide is nothing more than a periodic oscillation in the height of ocean water under the influence of gravity. Because the moon is closer to the Earth, the majority of tidal force is a result of the moon orbiting the Earth. This is why tides are periodic and predictable. A tidal generator simply converts this period rise and fall of ocean water into electricity. There are three basic mechanisms (though many variations on each) for harnessing this energy.
Dynamic Tidal Power
These are suitable only for certain regions because they work on a complex hydrodynamic concept that is most accessible in shallow ocean settings. Basically, dynamic tidal power interferes with tidal wave patterns that run parallel to the coast. These systems have yet to be tested, but have very high theoretical power outputs (one DTP dam could supply enough energy for ~3 million Europeans).
This system is much more like traditional hydropower in that it uses the potential energy that results from the difference in height between high and low tide. The system generally works by creating a pool that fills during high tides and then drains through a turbine as the tide goes out.
Tidal Stream Generator
These systems use the kinetic energy of moving water to move turbines in a manner very similar to that of wind turbines. These systems work as long as water is moving, so they generate electricity as the tide goes in and as it goes out in a given location.