Wave power and tidal power are not the same thing, so understanding the difference is important to understanding exactly what tidal power is. Wave energy is energy transported by ocean waves and has nothing to do with the ebb and flow of tides. Waves are generated as a result of wind and not generally as a result of gravitational forces from the moon and sun like tides. Despite these differences, the power harnessed from each of these forces can ultimately be traced back to the force of gravity. In fact, all hydropower solutions, besides ocean thermal, have their origins in gravitational forces.
Wave power is generated from the bobbing motion of objects that float in the ocean. Energy from the wave crest itself lifts the object against gravity endowing it with potential energy. When the wave crest passes, the object falls into the wave trough, which translates its energy from potential to kinetic. This conversion can be used to manipulate a mechanical device and thereby generate electricity.
Another method of generating energy from waves involves a combination of wind and water energy. Water from the wave rises up inside a chamber, thus displacing air. This, in turn, pushes a small fan that generates electricity. When the water falls, air rushes back into the chamber and turns the fan once again. Such systems are generally only found in small-scale applications.
The concept of wave energy was actually considered as far back as 1799, but has gained little interest compared to other forms of energy generation due to the difficulty of maintaining equipment and generating large enough quantities of electricity at an affordable price. Wave farms that are used for testing the concept of wave power can be found in Portugal, the United Kingdom, Australia, and the United States. Currently, the only real application of wave power is in buoys that have lights or GPS tracking embedded in them.