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What are the limitations of extracting energy from:
a. The wind?
b. Waves?
c. Tides?
 
a. The wind:
One of the wind energy limitations is that the windmills require a speed of  to produce electricity. And the number of windmills will be  to cover a vast area.
 
b. Waves:
To get the energy from the waves,  ocean waves are required.
 
c. Tides:
To extract energy from the tides, the sun, the moon and the earth should be in a  alignment, and the tides should be .