Like with all vehicle tiles that use or produce power, it says so when you try to install it:
As for solar efficiency, I was going to state that there are really good ones out there already and just recenty there was a new record set for perovskite/silicon tandem solar cells, but it looks like I’m late to that party…
To my knowledge; yes. At least it did in older versions, where I had problems to drive for long distances during the winter as it was overcast more often.
Well, given that Bertrand Piccard even flew around the world (although not in one go), I guess it would be possible, although really expensive and not really worth the effort (as you could usually recharge your battery relatively easy).
Some more research later… there’s the Lightyear One, a real solar car which has 5 m² of solar cells all around its body and it’s expected to charge the battery to offer an additional 50 km per day (with a range of 725 km, not sure if the 50 km are included in that or not).
While I’m not able to find the exact capacity of the batteries or power output of the solar panels, the homepage of the car states it uses 83 Wh/km and 1 hour of solar charging adds 12 km. So, that’s close to 1 kWh per hour, or 1 kW output (which would mean the solar panels/cells have an efficiency of 20%).
Now to answer your base question: Why does it look like to be so much more efficient in the game than in real life, even if - based on the numbers - it clearly isn’t? The answer: You don’t drive that many kilometers (and not as fast) in the game compared to real life.
For a “city car” that you use for short trips to your local store and home, it would clearly add enough charge every day to keep it going endlessly. But it wouldn’t make much sense to use solar cells on it, as you can just plug it in when you get back home. The efficency for perfectly mounted solar cells is much higher than on a car roof, so you’re better off by installing these cells on your home’s roof and charge a battery that charges up your car when you get home (and you can use the stored/leftover energy for other stuff too).