I am building my own Solar Ebike battery charger, using an "Off the Shelf" Itek 280W Solar PV Panel. It produces 171.3Watts of energy per square meter, and it's dimensions are 39" x 65" It has a PEAK efficiency of 17.13%.
http://www.solardesigntool.com/componen ... sheet.html
While there are certainly higher efficient solar cells out there, I think most are under 25% peak efficiency.
My Ebike battery will be a 16S (60V Nominal) x 32Ah RC LiPo pack, and will have 1894 Watt-hours of Energy capacity.
Assuming my solar panel produces the maximum output of 280W (It won't), and my DC-DC converter is 100% efficient (It isn't), it will take 6.7 Hours to fully recharge this battery. In reality, with a good sunny day, I expect it to charge at about 1/2 of that rate, or hopefully 140W to 160W. As such, it would probably take 2 full days to recharge from empty. - With my 1.5 square meter Solar panel.
I think you will find that to provide a "reasonable" amount of solar charging capacity, you will need a pretty large solar array. Making a wheel or two with solar cells will not get you very far, very fast.