Originally Posted by
ItsJustMe
I'd probably go with solar, if you can get a big enough one on top of your cargo. Lighter and doesn't cause any drag.
Drag is effectively a non-issue with modern genhubs. They're efficient enough that losses are equivalent to climbing a couple of extra feet over the course of a mile, and thus not even remotely noticeable.
The only downside of my relatively inexpensive Shimano genhub is a slight vibration between 17 and 19 MPH. Slower and faster than that, the vibration disappears. And I very, very rarely go at that speed when touring. ;-)