For some time now. Wild wet and wonderful PA, one of the cloudier area, has been using Wind and solar very effectively for some time now.
Solar has an unexpected use. End of line extensions. When there isn't enough ugga-duggas left to meet demand at the last sub-station, solar comes to the rescue.
Placing panels is so much less expensive than getting new right of ways, running new lines, maybe even moving the substation, when new housing developments and businesses need their electricity. And please people, storage batteries are no longer science fiction. There are even bolt on solutions for arrays that don't have tehm now.
Then there is wind. There are places where the wind never stops, the Allegheny Front for instance. At this point, our new wind installs are less than before. The reason? At the moment, what we have now are supplying the power we need at the moment.