But solar panels you can slap on a building roof or make into covered parking will always be
cheaper than form factor panels installed in the roof of a vehicle. Other than super specific fringe use cases, there is just no reason to justify installing these expensive specialty panels in cars
instead of installing them at homes/workplaces/retail centers and just charging EVs at those locations.
There is also the cost savings in scaling. The cost for a solar system comes down even more when a business can install a whole row of solar panel covered parking, either offer EV charging as a perk or charge for charging, and use the rest of the electricity to power normal electric operations. For the driver, buying the electricity as needed from home or work panels would always be cheaper per total watt usage than buying in-car roof panels, since again, the specialty nature of them means they will always be more expensive and less efficient than their stationary mounted counterparts. You can never scale up car roof solar because you can never install move than one car roof’s worth at a time. You also can’t ignore the inverter power loss that is much worse at the lower power a car roof system would have.
Then of course you have the downsides of long term sun damage to your vehicle to get that minimal charge, instead of protected under a solar panel covered parking or in a garage with solar mounted on top. You have the higher rate of damage by being installed on a moving vehicle instead of a stationary object on a building or parking structure roof. You have the lower rate of return, since panels are rated for 20-25 plus years and most vehicles don’t stay on the road that long. You have the downside of sub optimal charging angle and all the time the vehicle spends in a parking garage during the day, as opposed to a stationary panel that is pointed at the sun 365 days a year. At the end of the day, it will always be cheaper and more efficient to have stationary solar panels.
Given that most people charge their EVs overnight/during work anyway, car roof panels would only really provide value during “road trip” situations, where you are driving close to or beyond at full charge per day. Since you are only getting at best 10-15 additional miles over an entire day in the sun (and more realistically less than 10), it would do very little to reduce range anxiety. And that is not even calculating how much the additional weight of the panels would reduce range.
It sounds good on paper but it is highly unlikely to translate to a real world benefit.