In reply to BusyLizzie:
I have an Anker Power Port Solar*. We use it to top up the power banks and walkie talkies when family camping. It it's sunny, it seems pretty good, though getting the angle right seems key for good charging Works great hung on the tent while we are out for the day, it's also pretty light.. However...... how long will you be away from power, will you be in the uk and are you intending to attempt to charge whilst walking, i.e. hang it off your sac?
If you have access to power every 5-7 days, a decent power bank would suffice/be better imho.
If you are in the UK and won't have a "base" to set up to charge for a while, I think a power bank would be better imho.
*https://www.amazon.co.uk/Anker-PowerPort-2-Port-Charger-iPhone/dp/B012VL20G...