There are certain limitations to harness energy from the sea. Those limitations are

a) High dams are required to be built to convert tidal energy into electricity which incurs lot of cost.

b) Very strong waves are required, which are not possible all the time.

c) Tidal energy depends on the relative positioning of the Earth, moon, and the Sun.

d) To harness ocean thermal energy the difference in the temperature of surface hot water and the cold water at depth must be 20°C or more.