By far, the easiest is just to get a solar setup at your home/garage, tie it to the utility and keep plugging the car into the wall. Standardized parts, trained labor pool/ready contractors available, you can get home improvement loans to do it, easy to use, adds resale value to the home... list goes on. You certainly can put together a bespoke system that did nothing but charge a car, but... lately, that's the difficult and expensive way.
Are you trying to charge the car directly from a panel on the roof during the day? Yea, the 5 kwhrs or so to get that daily would require roughly 625 watts minus 10 percent for conversion etc. or Roughly 2-3 large panels.
I do have a solar setup on my toyota rv which I can charge my prime from- 600 watts on roof , another optional 600 watts on rolling yard cart which can plug into rv, 6 100ah lithium batteries, 2200 watt inverter. On a sunny day this will store enough to charge prime fully once a day on cloudy days/winter maybe only once every 2 days- really just depends on sunlight obviously. It's worth it to me as it also can act as backup power for house and can run everything in rv while traveling- even roof ac while driving.
Well if your plan is to install on the RV and you are using batteries to store the power. you'll be looking at around 20 percent for losses on the conversions. I would probably opt to install a bunch of lithium ion batteries for the sake of weight. If you can get the Tesla batteries that would probably be the cheapest method. You have to work around the voltages a bit for converting. But with the right power supplies everything should work out just make sure you include something to keep the batteries temps within range to prevent thermal runaway.
