i dont have experience w/ solar chargers. BUT, to save weight, i killed two apps with one stone.. heh.
on the android galaxy s5, i downloaded HAZ Tracks. this negates (somewhat) the need for GPS.
and i got an ANKER 7500 maH battery/case for it, that lasted 5 days on power save mode with normal operation time (surfing, some gaming, videos)
so, i cannot answer your original question, but if you needed a solar charger for phone AND gps you could combine the two, still bring a charger and only have to use it every 2-4 days.
in my case, i saved the weight of a GPS and charger for most 2-3 day trips, and gained 6oz, but probably shaved 16 to begin with. ain't ultralightin' fun?