Energy from the oceans can be tapped in three different ways,

(i) Tidal energy.
(ii) Wave energy.
(iii) Ocean thermal energy.

(i) Tidal energy: Dams are constructed across the narrow openings in the sea and, the tidal energy can be harnessed using these methods. Such sites are limited and the electricity generated is not high enough to be commercially viable.

(ii) Wave energy:Kinetic energy of the air movement causes winf energy.
Such sites in the world are limited where the waves strike the shorelines with sufficient power.

(iii) Thermal energy: To convert ocean thermal energy into electricity, it is necessary that a difference of more than 20°C temperature between the surface waters and water at depths of 1000 metres is required. This process is not economical.