Edit: Grid scale solar is its own thing for many reasons, one of which is not sticking things in a roof tends to dramatically lower risks and costs. But another is they are significantly more optimized.

> could both not be oversized on sunny days and cover usage on cludy days?

That isn’t a problem that’s worth trying to solve. Grid solar power is so cheap you can waste 70% over a year (even more on sunny days) and in many areas still be paying less than coal per kWh.

Ultimately the grid doesn’t care about being oversized for specific days. There’s a wild difference in demand on sunny day in the summer vs a day that’s 70f. When it was 70f in the 1970’s they didn’t go out and destroy nuclear reactors or coal plants because they are unnecessary in May. That’s valuable infrastructure even when not in current use.

The only metric grid operators care about is does this grid design need the demand and what does it cost. Peaking power plants exist to fit edge case demands even if not used for months at a time, “peaking solar” isn’t a term anyone uses but solar + batteries can fit that niche.