Modern dyno-hubs are alternators, put out AC, so a full-wave bridge rectifier
is then part of the system to DC the AC..

solar panel is DC .. , a battery, charged, in common, seems the thing to include.

It should be apparent that you are adding to a market where those things already exist..



A gimbaled maximum solar input seeking (powered) solar panel holder
would be a clever thing
to be towed as part of a bike trailer.. since in motion keeping the large enough panel
at a right angle to the sun as it transits over the day , on moving vehicle is another issue to tackle.

Oh and make it nearly weightless..