I read someplace that about 15% of grid power can be supplied with solar or wind. Much more that that, if the wind does not blow or skies are overcast, the grid gets unstable, overloaded and crashes. It is not really feasible to have a coal, nuke or gas fired plant on standby to make up any short fall as you would have to have crews on standby to run them. If you have to pay the crews, you might as well use the plant to generate power in the first place.
The small mini-nuke plants have a new design that makes them a lot safer than the traditional large nuke plant. If the mini plant overheats, the design is such that the reactive material is forced apart and the reaction is stopped, so it can not melt down.
Down side is that building a bunch of small plants is more expensive than one large one. Another downside is that securing many small plants is a potential problem that would require a large number of security officers.
Dave