Tidal energy
The periodic rise and fall of water level of sea is called tides which are caused by gravitational effect of moon combined with the rotation of the earth. This variation in the sea level is utilized for the generation of electrical power is known as tidal energy.
The tidal can be harnessed by constructing a tidal barrage. During high tide the sea-water flows into reservoir of the barrage and which turns the turbine to produce electricity. Under low tide water from the reservoir flows back into sea and turns the turbine again to generate electricity.
Advantages:
1. It is renewable source which uses inexpensive sources (water) to generate electricity.
2. It is reliable source of energy.
3. It does not produce pollution.
4. It is highly efficient. (80%).
Disadvantages:
1. It is expensive to construct tidal barrages.
2. Power is generated such places, where there is little demand for electricity (coastal areas).
3. Barrages may affect aquatic ecosystem.
4. Transportation of electricity is problematic.