you may not *need* the solar, but solar power is "free" where the alternator costs money to run
I'm a big solar fan, I read the diysolarforum.com vehicle mounted forum daily, I've got all that goodness on my truck camper...
... but solar is far from free! The panels are expensive, and the glass ones you should use are very heavy. Flexible ones don't seem to last long. They all create airdrag and extra weight I have to cart around on my truck 24/7. Not gonna do the calcs, but I'm pretty sure they waste waaaaaay more gas carting them around 365 days a year, vs the extra gas I burn the few days a year I use my alternator charger! Pretty sure the solar costs more than alternator if we look at the true total picture.
I have 450W solar, and I stopped carrying it in truck. My use case makes them pretty worthless to me. While sun is up producing, 10am to 3pm maybe, I am driving around, and 95% of time that will be in shade in forests. All the overlandlanding folks I know have similar usage patterns. Solar is great for 3 days or more parked in the sun.