They’re almost always S-curves; but no one knows where the inflection point will be.

Probably https://news.ycombinator.com/item?id=42266903 provides some useful clues about where the inflection point will be. 2 terawatts is about 1/64000 of the 128000 terawatts of ground-level insolation. Probably people will not cover literally every square meter of the planet with solar panels, but why would they stop much short of that goal?

In Shandong they're already building a 1-gigawatt solar farm offshore, 20 years earlier than I expected people to start doing that: https://www.youtube.com/watch?v=l_MlFOizMBo

The expected capacity factor for the Shandong project is 20.3%.