As simple words to say, a solar car is a vehicle purely/mainly powered by solar energy, no CO2, using only clean energy.
The Major Advancement
There has been solar car development; the World Solar Challenge (WSC), a 3000km solar-powered car racing started over 35 years ago, powered by purely solar energy. But they're far from production passenger vehicles. Those are only experimenting vehicles for a longevity test race held every two years.
Some designs evolved from WSC, such as Lightyear One (shown in the pic above) and Stella. Others, such as SONO Sino, Aptera, have developed their electric cars with solar panels. But none would be qualified to be called a "Solar Car" or "Solar Electric Vehicles" simply because their primary energy source is still from the electricity grid. It is just an electric car with solar panels, solar assisted. You may call them a "Solar-powered Car" at most.
What makes a good Solar Car
WSC solar car designs have three main criteria,
Vehicle efficiency – lighter vehicle, fewer components, high efficient motors, a restricted compartment space/seats;
Solar efficiency – high efficient solar modules and maximized surface coverage over the vehicle;
The perpetual sunshine solar.
As you can see, the criteria above for a solar powered EV are either not fit (except #3) for nowadays passenger cars or would significantly jet up the vehicle's cost. Can you sacrifice, say, the air-conditioning, the storage trunks, your automated comfy heated seats, the spare wheel, even your vehicle's performance?
You might say, "yes, I don't mind taking out some of them." That's good, and you might fit for some of the solar powered cars mentioned above with solar "glued" on the vehicle's surface. Eventually, every electric solar vehicle looks very much the same with a black surface if you think aesthetics is no problem. Let us know what you think in a year or two after you've got one.
Are We Ready Now
Don't get me wrong; this is a great start to the "Solar Car" journey. It just doesn't suit the majority as yet. It'll probably take at least ten years, if not more, to get close. In the meantime, solar panel, batteries, and battery charging advancement is the key to the "Solar Car" journey. However, an electric car with solar panels to become "solar assisted", is not something far reached by switching to BEV (Battery EV) or PHEV (Plugin Hybrid EV) while using solar recharging whenever possible.
Just don't expect it to recharge your EV fully at once. Hey, your EV manufacturer recommends you recharge primarily between 20% - 80%, especially at a fast charger, right?
In the meantime, solar charging your EV usually means using your rooftop solar with a battery system installed so that you can recharge when you get home. The ultimate goal is to solar recharge wherever you go, like a "Solar Car". I think the words "wherever you go" are very controversial. Not that "wherever you go" was wrong; it should read "wherever you parked".
More Practical Ways For Solar Recharging
Think about the time and duration you drive during the day. Most people drive in the early morning and/or late afternoon when the solar irradiance was weak—parked most of the time when irradiance was strongest. A bus or taxi would drive the whole day under the sun, not a passenger vehicle (your car), not even an Uber.
Studies already proved "Cars are parked 95% of the time," if not more. Further studies from IEA-PVPS (International Energy Agency - Photovoltaic Power Systems), a Worldwide research collaboration group on photovoltaics research, did a preliminary survey on car parking behavior in 2020. They found a similar result of over 90% of cars parked in the Daylight hours.
Parking on your driveway or anywhere under the sun is ideal for a solar panel car. By recharging more from your rooftop solar, your BEV would also become a "Solar-powered EV", just not an electric car with solar panels.
Solar-covered parking may be an excellent good way to go while we're searching for a better way of renewable transportation. Imagine every time you go shopping, it provides shaded cover and recharging facilities at the same time. Solar is the best bet and the quickest to free us from fossil to renewables.
I think solar recharging "wherever you parked" under the sun is a more realistic target. To achieve a world of "Solar Powered Car", solutions for solar recharging when you parked are worthy of attention.