One can now get (flexible-ish) multi-junction PV (say 29% efficiency) from the factory for under $1/W. Still a higher price than the $0.2/W, lower efficiency panels, but when I messed with panels I felt like we were living in the future.

Anyway, one could also set up the panel to output a much higher voltage by having the factory wire cells in series (though how well that trades off with partial shading for a car roof I have no idea, and I have no idea the minimum quantity required to get that).

... but I agree, even with all that, it seems like a stretch to make it work.