It makes sense. A fan powered by solar energy extracts hot air from the car while it is parked. But does it really work?
We purchased a unit and tested it for a couple of days. We found that the fan is relatively weak and consequently not powerful enough to lower the temperature inside the car substantially.
Further the unit has to be in direct sunlight to function. Another inconvenience is that the unit and the rubber seal have to be removed when driving to avoid loud road noise.
We do not recommend this product. The car manufacturers might however consider the idea and integrate a more powerful unit at the ceiling of the vehicle with a solar panel on the roof.