There are several reasons that I'd like to see a "self-unfurling car tent" that could extend from a car and cover it when parked, and "de-furl" itself when returning to a car.
Shield the car from sunshine
People are always trying to park in what (usually very limited, where I am) parking spaces that are shaded. Carry a reflective, vented tent, and the problem goes away; you've got your own shade everywhere you go.
There are already car covers:
But these don't self-unfurl and furl, so they're enough of a pain to use that most people won't use them unless they're parking their car for some time; manually deploying the thing on a grocery store trip isn't worth the effort. The most people will normally do is put up a windshield sun shade, which is a lot less effort to put up.
Solar panels become a lot more practical
Volvo had a prototype unfurling-from-the-trunk solar canopy over a decade ago; I haven't heard of it since.
That thing took up a ton of space, and wouldn't work in a parking lot, but something that closely-matches a given car model's exterior shape might be a lot more practical.
There are vehicles that have factory built-in solar panels now; the 2025 Toyota Prius PHEV has a solar roof option, for example:
But they don't provide a lot of surface area, because they can't cover the whole vehicle, just part of the roof, so provide a limited amount of power. That Prius can get a maximum of about four miles (6.4 km) a day of range from sun.
But you can put whatever you want on the exterior of a tent that's only deployed when parked; surface constraints go away, so now you have a lot more surface area to work with.
There are existing car covers that have integrated solar panels, but the solar panels on these are tiny, just designed to keep a car battery topped off when a car isn't being used for long periods of time; they aren't designed to feed a larger battery bank.
Hail resistance
There are some places in the US where hail is a real problem, where it damages a ton of vehicles every year.
Cars, which are normally rigid, don't do well with hail. Fabric-like materials, which are springy, do a great job. There are some existing car protection systems that fit onto a car that make use of this, have a little standoff distance to permit the hail to decelerate in, as well as fixed structures and manually-deployable static fabric hail protectors. Looking online, soft-top convertables will suffer damage to the body in hail that the soft-top roof can just ignore. I don't know how well hail resistance would play with flexible solar panels---might need to pick one or the other. But I'd expect at least one or the other to be possible.
Issues
There are some issues I can think of.
A big one is that car exterior surfaces are more durable than tents, and I can imagine accidental damage being more of an issue for the tent, like being cut or something. Maybe it'd be practical to make such a system out of modular pieces that zipper or otherwise easily attach to each other, and if one piece of the tent is damaged, just pick up a new one, detach the old one, and stick a new one in; no big deal.
Theft of the tent (or pieces thereof, if modular) might also be an issue.
Yeah, that's a fair point
one doesn't want to pack away a wet tent.
If it refurls into a dedicated compartment, then it shouldn't be an issue in terms of moving water into the cabin.
If someone always uses the thing when parked
which may or may not be realistic, then I think that it'd dry out as soon as the outside dries out.
One could also actively-dry the thing. As long as the fabric is porous, which it'd need to be for the sun shield application (so heat wouldn't build up), I expect that it'd be possible to pass air through the tent compartment. If you're a vehicle with an ICE of some sort
including a hybrid or PHEV
then you have waste heat from the engine that you're mostly just throwing away. You could use to blow some hot air into the tent compartment, same way cars presently do into the cabin, until a hygrometer reads it as dry. Would need to be the car manufacturer to do something like this, though, not like your aftermarket project.