(a) A windmill requires wind of speed more than 15 km/h to generate electricity from wind energy also large numbers of windmills are required to get feasible output which covers a large area.
(b) Very strong ocean waves are required in order to extract energy from waves.
(c) Very high tides are required in order to extract energy from tides. Also, occurrence of tides depends on the relative positions of the Sun, moon, and the Earth.
