I think the above is a very valid caveat to what I'm about to say ...

I carried a solar charger for most of my 2008 PCT thru-hike, one of those Solio models that opens up like a "three petal flower". I had cord tied to the top of my pack and just tied the unit on when I started hiking each day. The Solio has a battery built in, so during the day it charges the battery, then at night I would connect it to my phone to bring up the charge on the phone. Starting out walking north (so with my backpack on average facing south) in Southern CA (very little shade), it did okay, but it definitely did not give enough juice on a daily basis to fully recharge the battery, so I was still charging some in towns whenever I had the opportunity.

I hiked with another fellow who modified his Chrome Dome umbrella to firmly attach his Solio to that.

On balance, I think that walking north in SoCal it was worth carrying. In northern CA and OR somewhat less so, in part because I was then a bit further north, but more importantly there was more often some sort of overhead cover. When I finished Oregon I stopped carrying it.

On the AT I wouldn't consider it anytime (and didn't) --- too much overhead cover, and so many places to plug into an electrical outlet. On the CDT I briefly considered it but then opted to keep life simple, and I was glad that I did. A lot of sun on that trail, particularly in NM of course, but still --- I carried one spare battery for my phone and that was always fine.

It might be that solar tech now is sufficiently better than what I used in 2008 that they're more worth carrying, but I think that the dynamics of what you can get while hiking is uninspiring still. If you live in a sunny southern state and hike in places with relatively few trees it's a different story, and ditto if you're the type to base camp or otherwise spend a significant part of the day in one place.