So my two babies were standing in the sun for about 2 hours next to each other. Temperature was about 18 degrees in the shade, but of course much warmer in the light.
As I got into the S3 to park her in the garage I noticed she really warmed up inside, granted she is black, but still I started to sweat a bit.
Then I got into the RS4 and it was still cool inside. So the solar is doing its job very well in these sorts of temperatures. When it gets really hot outside it won't make much of a difference I'm guessing but will report on it during the summer.
Glad I ordered it.