Some good points here, sorry I came in late. I use solar panels, when I arrive on a site my battery is about 13.5 volts charged from car. when I leave a site after 1 week or 2 and after using lights TV etc etc the battery is 14.8ish
I would forget the maths and try a panel before poo pooing them, solar power and regulators have improved a lot.
In all the facts and figures no one has stated what type of regulator they use, if they are p.w.m. or even trackers
I suppose mobile phones, are just something to fill your pocket, hard work carrying the suitcase around with the battery, besides you cant get a signal unless you stand near a shop etc with the rabbit sign, (and we are no longer charged to receive calls)Dolly tubs have also gone they replaced rocks to clean our clothes on
Go on try a new multy crystalline panel, with new generation hybrid regulator. 40/50 watts to be on the safe side
you will be pleasantly surprised