It is possible to cover the entire parking lot or the roofs on all the surrounding buildings but I don't think the plan is to do all that.
wasn't there mention that those superchargers would be connected to a battery?
then they would not need high-power connection to the grid!
It still seems to me that the marginal cost of adding one to an existing Tesla facility would be significantly less than building one from scratch.
At a sales facility, I'd also think that potential customers seeing and talking to owners charging there would make them feel better and existing owners might wander through the showroom and think about another car or an upgrade.
As far as completely solar powering a Supercharger, that would seriously not work in many areas of the country, e.g. New England. After the first few days of overcast weather with intermittent sleet I don't think there'd be much charging going on.
In fact you aren't going to bring in that much power on 480 3phase anyway it requires too much copper, you are going to bring in much higher voltage and step down near the supercharge units.
www.Power12.com ----- Sweet Silver Sixty: 60KWH, Non-perf, Silver ext/Black int, Pano, Tech, 21" Silver wheels