A dynamo is far simpler & the best option for your requirement. The thing is all this Solar Panel thing-ma-gig will only complicate matters for you, and what if then it doesn't workout as you need it?? Hub Dynamos are really one of the most efficient bicycle-power generators out there. All you need to do is get one.

I've been using Shimano Hub dynamos & now I never have to worry about draining batteries on Garmin, Mobile phones and yes even lights