Yes on the beauty of using solar photovoltaics for flashlight batteries, and very good feeling to charge the ebike with the sun. What Stefano said about having to reset when clouds happen, that is important.
Consider getting a larger solar panel that can be in position all the time to receive power. It can still be portable (or not). At a later stage, get a substantial means of electrical storage (with a charge controller), whether lead acid or lithium based. Now you can run much more than a flashlight; stereo, TV, indoor lighting, fan, something else you have. You never know when it might come in very handy under abnormal circumstances.