the goal0 nomad 13.5
http://www.goalzero.com/shop/p/12/No...lar-Panel/6:3/ is the only panel i have experience with and it will charge in almost all light conditions and its very powerful but its heavy and expensive. I think the only charger that youll find worth it to charge your phone will either be heavy expensive or both. There's also
http://www.npowerpeg.com/learn-more which is a little tubular thing that captures your kenetic energy as you walk and move but it is also like $120, its free and light energy but i dont think it will charge your phone very fast as it says it takes 25min of walking for 1 min of smartphone talk. just my 2cents