The issue is that solar is produced when energy is cheapest during the day, and during the night when everyone returns home energy surges.[1] This means that the grid has to include non-solar backup generation that can exceed the peak generation of all the solar on the grid.
The real breakthrough for solar will have to come from energy storage advancements, such as cheap neighborhood-scale batteries. This will allow the energy created during the day by solar to be used at night when demand peaks.