Powacycle, the brand behind Infineum electric bicycles, is developing solar charging panels to work with its stackable battery packs.  The super-slim batteries, shown on the bike above, can be increase by simply stacking another slim battery on top.
They’ll fold up when riding.  Once you’ve parked the bike, open them up to collect sunlight and charge your battery.
This should increase the useable range of their e-bikes since they can recharge at the destination, too.  Well, maybe not in Seattle…