I'm not totally up to date on theoretical solar panel efficiency, but last I checked you could get about 250 watts about of a 3x5 foot panel. Let's assume Model 3 can generate two panel's worth of power.
A standard outlet (NEMA 5-15) can charge the car at 1,400 watts and adds 3 miles per hour of charging time.
2X a single panel would generate 500 watts of power. Assuming similar efficiency between solar and the UMC, the solar roof would charge the car at 1.07 miles per hour.
If the car was parked outside for a full workday (8 hours), it could add about 8.6 miles of range assuming conditions are ideal for solar panels (sunny day, summer time, etc).
This would indeed be pretty cool, but I'm assuming the cost of such a charging set up + solar panels would greatly outweigh the benefits.
I'm not sure I would pay anything extra at all for such a slow charging rate, when at home the vehicle is connected to an HPWC and
charging at a comparatively-supersonic 48 miles per hour. It would take just 11 minutes of charging at home to add the same 8 miles of range.
Thoughts?