(i) Tidal energy — the energy possessed by rising and falling water in tides is known as tidal energy.
But this is not a major source of energy because of the following two reasons —
- The rise and fall of sea water during tides is not enough to generate electricity on a large scale.
- There are very few sites which are suitable for building tidal dams.
(ii) Ocean — Water in oceans possesses energy in two forms:
- Ocean thermal energy — The energy available due to the difference in temperature of water at the surface and at deeper levels of ocean.
- Oceanic (or sea) waves energy — the kinetic energy possessed by fast moving oceanic (or sea) waves.
(iii) Geo thermal energy — The heat energy possessed by rocks inside the earth is called geothermal energy.
It is harnessed to produce electricity. The rocks present at hot spots, heat the underground water and turn it into steam, which gets compressed at high pressure between the rocks.
By drilling holes into the earth up to the hot spots, steam is extracted through pipes which is utilized to rotate the turbine connected to the armature of an electric generator to produce electricity.
