What are the limitations of energy that can be harnessed from the sea?

The limitations of energy that can be harnessed from the sea are as follows:

1. To obtain electricity from wave energy, very strong waves are required which are not available in the sea all the time. 

2. To harness ocean thermal energy efficiently, a temperature difference of 20℃ or more is required between the surface water (hot) and the water at a depth (cold).

3. Tidal energy depends on the relative positions of the earth, the moon and the sun. Also, very few sites are suitable for building tidal dams.