There is a three-part method for this:Karma 2012 said:
(1) get out of the car
(2) look up in the sky
(3) if you can see the sun, the solar panel is working
Just kidding, of course! Actually, the Solar section of the command center is intended to display the current and historical data on amount of energy generated and captured by the rooftop solar panel. You may currently have a static screen showing a "star pattern", fixed on a particular month of the year, which may be the case in some (if not most) cars. I was told this is something being de-bugged in the next software release.
Also, remember that the panel is primarily intended to run the battery's cooling system on a hot day, while also avoiding having the battery run down. So unfortunately, in my view the best test of the panel will be when summer comes and I can park it on hot asphalt at WalMart on a 105 degree day, set the car to cool the cabin (double-click the lock) while also cooling the battery, then come out in an hour and see if the cabin is cool and the battery range has not declined.