On-road charging with solar is a pipe-dream in anything resembling a conventional car or motorcycle.
Here's one of the most well-executed
solar bike designs I've seen:
Its onboard solar panel (home-built from individual cells) is good for somewhere around 100W. On a low-weight recumbent bike, that'll get you moving at around 8 mph using only solar power. On a freeway-capable e-motorcycle, it'll power your headlight and a bit more.
Put another way: if you ride for an hour on an electric motorcycle, the solar panel would get you about a mile of extra range. The aerodynamic tail would have more benefits for increasing range than the solar panel would.
Now, left outside to charge on a workday? You'd pick up maybe 4-5 extra miles of range, or a bit more on a sunny day. That's not terrible. If you had room to spread out some
thin-film panels (see
previous discussion), you could seriously mitigate your need to charge, at least in the summer.
Here's a
version with deployable wings which he thinks will get 70-100 miles on solar per day:
My normal commute is 25 miles @ 45-55 mph, uses around 3.3 kWh at the wall. North AL gets around 4.5 hours of sunlight averaged over the year, maybe as much as 6 hours in the summer. To recover all the energy for a typical commute, I would need around 800W of panels to fully charge on a typical sunny day. Using the same Powerfilm thin film panels that solarstik uses, you'd need about $10k in panels (which weigh 50+ lbs and unfold to around 20' x 12').