[actionfromafar]

There was some car which used a small solar panel to pass fresh, cooler air into the cabin during sunny days. This both made the car more pleasant to enter and lowered the initial AC surge. I don't know if it also trickle charged the starter battery so it never could get completely depleted from just standing for longer periods. Both these things seemed worthwile.

[pyk]

The 2010 Prius IV had this as an option - one of my favorite cars due to low maintenance (the lowest maintenance visits per year for its era). The solar panel air vent circulation is a nice feature (even if slightly gimmicky) and I suspect extends the hybrid battery life as well by preventing some marginal battery heat death while parked.

The newest (2023+) Prius brought back the solar roof as an option - and this time it charges the battery (albeit marginally / but not bad for those that drive minimally).

[eldaisfish]

A more practical solution is to leave the windows slightly open so the hot air escapes.

[gabrielhidasy]

There are places where a marginally open window will invite vandalism, or rain, or bugs, or smoke and bad smells.

[eldaisfish]

ok, so in those places, you don't leave a window gap. in all the other places, you do.

[SoftTalker]

Not practical if rain is forecast.

[imp0cat]

The car already has a rain sensor so it can close the windows automatically. I do believe some VWs already do/did that.

[SoftTalker]

My car has that to activate the wipers. To say it works reliably is to lie.