There's still sun during the winter; you just need more solar panels for the same amount of energy. Also, there tends to be more wind during the winter, so wind power makes a good complement to solar.
My larger point is that solar is only ever going to be a piece of the puzzle at best. In space it might be quite nice, but otherwise it's kinda goofy to invest too much in.
Doesn’t that apply to any power source?
Short-term we're waiting for mass production and distribution of the new designs (relatively easy to predict), not R&D which is less predictable.