I have followed the development of portable, and affordable, solar panels with interest – even haute couture. There are good panels available from Brunton (who also have good guides to power usage); Sunware (27 watts); Sunsei (2,6 and 18Watts); and of course for small devices like mobile phones and true portability there is Power Monkey and Freeloader.
As a matter of interest I have been using Power Monkey both in the car and on the boat since 2007 without a hitch.
I see there are even more powerful – portable – offerings now on the market. Such as the PowerFilm F15 – which packs a tremendous 60watts.