Well, that is a very fudge-able thing. 90+% of solar systems are offset (net-metering) systems where excess beyond what is used in the house/business/charging station at the moment of generation is sent on to the grid, and is used to offset energy that is drawn from the grid when solar generation is insufficient. Over a period of time you true up your net usage (or generation) with the power company. It is completely possible that Tesla's supercharges could ALL be solar powered in the sense that SOMEWHERE Tesla is offsetting the power drawn from the grid with power sent to the grid.
Al, you probably know all that… not trying to correct you, but to point out that it could be considered solar powered even if it is not connected to panels.