Amazing how folks have forgotten the discussion that went on right in this TMC forum several years ago, where the consensus was that it was eminently possible to make a profit from selling the excess Supercharger solar electricity back to the grid. Many superchargers outside of major population areas like California have very little traffic, maybe one or two cars per hour, while the sun is beating down the whole time, and the battery would get full pretty quickly.
Here's Elon in May 2013: Tesla Planning Grid Storage As Part Of Supercharger Expansion
There is a difference between profitable with selling excess energy (while charging for charging) and being self support purely on excess generation. (In the macro view, the extra will be powering the sites without solar).
With production going up 6x this year, those chargers are going to see more use. There is also the demand shift factor of preventing excess usage due to it being free vs home charging. If it is at parity with home charging, it will only be used by those on long travels or unable to have at home/ work charging. Also provide common price expectation of urban vs plaza chargers.