Unless some very serious technical breakthroughs happens in more efficient manufacture, energy capture efficiency and energy storage, by the point that around 1% of Earth is covered in solar panels, Earth probably ran out of "useless" land space and materials to make solar panels and the associated infrastructure to actually use said energy to something useful.
That's rather the point; tech breakthroughs happen when there is a drive to achieve something, increased demand for solar causes that pressure to strive and thus increases the likelihood of innovation. The more panels that are built, the better we get at building them, innovate, repeat.
