To make it clear, I am not saying that solar panels don't work, of course they do. What I was questioning is using a solar panel over a power bank of the same weight.

A 20 Ah (77 Wh) power bank weight about the same as a 15W solar panel. That about 3 full (0-100%) charges on a typical smartphone. I think that would have kept your wife phone up the whole trip no problem, and no need to worry about the sun.

On a 11 day trek in the sun, yes, by all means take a solar panel. However, most people I know who do such long hikes usually have access to electricity at some point. But if it is not your case, well, you are the reason why these solar panels exist ;)