Tidal energy,

sometimes called tidal power, is the power achieved by capturing the energy contained in moving water in tides and open ocean currents.
There are two types of energy systems that can be used to extracted energy: kinetic energy, the moving water of rivers, tides and open ocean currents; and potential energy from the difference in height (or head) between high and low tides. The first method - generating energy from tidal currents - is becoming more and more popular because people believe that it does not harm the environment as much as barrages or dams. Many coastal sites worldwide are being examined for their suitability to produce tidal (current) energy.

Tidal power is classified as a renewable energy source, because tides are caused by the orbital mechanics of the solar system (ocean currents are caused by the surface effect of winds) and are considered inexhaustible. The root source of the energy is the orbital kinetic energy of the earth-moon system, and also the earth-sun system. Tidal power has great potential for future power and electricity generation because of the essentially inexhaustible amount of energy contained in these rotational systems. Tidal power is reliably predictable (unlike wind power and solar power). In Europe, Tide Mills have been used for nearly 1,000 years, mainly for grinding grains.

Wave Energy

Waves are generated by the wind as it blows across the sea surface. Energy is transferred from the wind to the waves.
Wave energy is sometimes confused with tidal energy, which is quite different.
Waves travel vast distances across oceans at great speed. The longer and stronger the wind blows over the sea surface, the higher, longer, faster and more powerful the sea is. The energy within a wave is proportional to the square of the wave height, so a two-meter high wave has four times the power of a one-meter high wave.

Why Wave Energy?
Wave energy has the potential to be one of the most environmentally benign forms of electricity generation. It is a clean and renewable energy source and its potential is huge. Some additional benefits of wave energy are:

1.  With the wave energy resource distributed across the globe, wave energy offers many countries the benefit of security of supply
2.  Waves are generated over large areas of ocean and, once generated, travel immense distances with only small energy losses.
3.  Waves can be anticipated one or two days in advance through direct satellite measurements and meteorological forecasts which provide a high level of predictability and hence good network planning.

SOURCE:- Wikipedia.org , pelamiswave.com