This is simple, but where do you think the 7 volts difference between the panels and the ipod goes? Into waste heat. If you are electronics capable, its a much better option to make a switching regulator.
this stuff is the biz! the military USB+AA is on my list. I will probably ditch the laptop if it is a longterm SHTF, all my info, pictures and music are on my ipod, aa charger will be handy for led torches etc.