Your solar panels are trying to gather heat and gather it at a high temperature. The engine’s cooling system is trying to get rid of heat and to keep a lower temperature. Yes, if you want your car’s cooling system to run at 300F rather than 180F, then there may be an advantage to keeping coolant in the engine longer.
To simply move as much heat as possible, move the coolant faster.
Unless you are talking about Robert’s second scenario above, you would be incorrect.
There was a discussion on this some time ago
Fact/Fiction- cooling - E-Type - Jag-lovers Forums
Tom