When you build a capacity of 100MW, you are not going actually gain 100MWs in actual energy. Take a look at the 1000MW solar project that Pakistan is building; right now, only 100MWs has been added, and out of the 100, only 10MWs is useful, due to inefficiency of solar energy, thus a 10% efficiency rate. More expensive panels can take that up to 15% and even 20%, but the financial cost would be enormous.
A similar problem is with Wind, which could give you a lot of enery, or give you nothing, depending on how strong the wind flow is.
Hydroelectricity, you're literally giving up a vast amount of land, to build water resources and increased energy.
Nuclear, far too expensive to build a lot of power plants, plus it carries a lot of geopolitical baggage.
---------------
Admittedly, renewable energy has become cheaper over the decades, and is making strides in efficiency, going from 20% to 35% in a few years....
http://www.sciencealert.com/engineers-just-created-the-most-efficient-solar-cells-ever
...but the issue is that more efficient panels (including the 35%), that compete with traditional power sources, are still a decade away from being consumer ready.
I hope that made sense, I'm still half asleep right now.