I've seen a lot of people asking if there will be a solar-powered charging option for their Storm Electric BIke and it makes me realize the general population doesn't realize what a PV panel is actually capable of.
Solar:
Basically under ideal conditions you will get 1,000 watts per square meter (and really the commercially available panels aren't this efficient at all, they perform worse) of solar panel at the equator, at noon, with zero cloud cover. That means for the 350 watt hour battery to charge in an hour you'll need 542.501 square inches of PV panel to charge it in 1 hour's time... so you aren't going to just fold a small PV panel up in your backpack and set it out at your destination to charge the bike. Fore more information on solar power, see the bottom of this post for some good educational links.
HOWEVER if you are going camping or in the event of an extended power outage (keep in mind, solar panels only work if the sun is shining, storms can create cloud cover for days or weeks meaning no sun) want a way to charge the battery in a timely fashion to give you the ability to greatly increase your area of operation during the power outage, you CAN get a smaller panel which will charge the battery over several hours.
Something like the RenogyⓇ Foldable Solar Suitcase Battery Charger 100W for a good portable option