taking a junk car plower fan and heter core box you could easly build this in your hatch or trunk and then pipe the suction side to the top of your cars roof,(you wan to take the air from the top as heat rises) then blow it out of the car .. the car should then suck in fresh air from the cowl vent.. it might just work .. youll need some decent powered solar cells those blowers take some decent power.
here is a 12v blower assembly.. draws 5.1 ampt , thats 61 watts.. 80 watt solar panels are $400+ bucks..
Surplus Center Item Detail