I ran a Honda XR600 as my long distance bike for many years and as you may know, that's a direct ac system without a battery. Quite honestly it was a pain in the a*se. You couldn't do anything without the engine running - and not much more when it was. I did eventually fit a small battery with a rectifier just so I could run stuff like led camp lights, sat nav etc.

Most of the time though I had to charge cameras, phones whenever I stayed in a hotel. I've tried solar chargers a number of times but in my experience the sizes you can accommodate on a bike just don't work. Maybe the door sized one you can bolt onto a Land Rover or similar might be different but if you're considering those you might as well just stick a battery on the bike.

I have had a bit of success with a small wind generator sitting on the handlebars. The fan charges up a small internal battery which will then power anything with a USB port. It won't charge it up but you can use it.

I'd guess if you're considering simple electrics then the bike'll be kickstart only. I've no idea what engine you're considering but kickstarting the XR regularly on a long trip eventually became something I detested doing. When I was tired or I stalled it in traffic I could quite happily have set fire to it and walked away. Something that requires less effort (smaller cylinders) might have been ok but the XR required a kind of ritual otherwise nothing would happen.