What are the limitations of enegry that can be obtained from the oceans ?

Explanation

The energy from the oceans can be obtained mainly in three forms : Tidal energy, Wave energy and Ocean thermal energy. Some of the important limitations of these forms of energy are as follows :
(i) There are very few places around the world where barrages (or dams) can be built to harness tidal energy. Moreover, the rise and fall of water during high and low tides is not enough to generate electricity on a large scale.
(ii) The wave energy can be harnessed only at those places where the sea-waves are very strong. The efficiency of power plants based on wave energy is very low. Moreover, the power plants built in oceans or at sea-shores have high cost of installation, corrode easily and need a lot of maintenance.
(iii) A temperature difference of `20^(@)C` (or more) between the surface water of ocean and deeper water is necessary to harness ocean thermal energy. The efficiency of OTEC power plants which work by utilising ocean thermal energy, is very low. Moreover, it is very expensive to establish OTEC power plants.