What are the limitations of extracting energy from - (a) the wind? (b) waves? (c) tides?

(a) Wind energy is harnessed by windmills. One of the limitations of extracting energy from wind is that a windmill requires wind of speed more than 15 km/h to generate electricity. Also, a large number of windmills are required, which covers a huge 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, the occurrence of tides depends on the relative positions of the Sun, Moon, and the Earth.