renewable energy limitations?

billrussell42 Answered:
They are not reliable.

solar energy is available only when the sun shines.
Wind energy only when the wind is blowing
tidal energy only at the peak of the tide.

fuel from corn takes away food from a starving world.
Trees are very limited in amounts and time to grow back.

And they all require locations that maximize those variations.

But the power demand is continuous.

Raymond Answered:
That is a good answer. As we approach exclusively, the cost rises rapidly. We could build a world wide electric grid using HVDC = high voltage direct current power lines, which would solve most of the problems of wind not blowing or sun not shining.
With 4 impounds, tide can produce continuous power, except rarely when the wind cancels a tide change. Space based solar power satellites, Gulf stream flow = OPEC, some rivers and geo thermal, can produce power 24/7, but are too costly in most locations. Fossil fuel generating systems also suffer rare unplanned shut downs.Neil