Which means on a 8 hour day I get to charge around 6 cars? With angle of sun and other efficiency losses, it is probably even less
That's only two out of the five arrays, but you're general observation is correct - the solar arrays are not capable of replacing the grid at Tesla's Supercharger stations even on the sunniest of days. This will be particularly interesting when it comes to the semi and Megachargers since Elon claims that they'll be sun-powered. I expect them to be grid-tied just like Supercharger stations. The solar panels will help reduce the peak, but they aren't enough to offset the entire operation unless you're attaching acres of panels to a charging location. Who knows - that might be exactly what they plan on doing.