If you boondock a lot and have low power consumption, solar can make a lot of sense.
If you stay at parks with electric or you have higher power needs, it starts to make far less sense.
Shade is a killer for solar. Because of the way they are wired, even a small patch of shade on a panel almost completely kills the output.
As far as cost...if it keeps you from staying at paid parks, it makes some sense but if you are boondocking regardless, the person who mentioned years/decades was correct. It's absolutely not free.