Hi, this would be the battery pack i would like to buy. (See below) I wanted to ask you guys first, before i make stupid decisions. What does the 50M stands for? Because i see on their website this make a big difference in the buying price.
https://enerprof.de/en/ebike-batteries/softpacks/36v-10s-batteries/435/softpack-battery-36v-15-ah-bms-20a-xlr-3-with-50m?c=90
If you can afford to get a good li ion battery then your range will not be a problem, so maybe sort that out first.
With your kit setup, you will be able to charge it with solar, quite easily, because you have not got Shimano or Bosch etc controlling your battery! But it will cost a bit, and has to be done carefully or things will break!
The main things you will need are a solar panel, and a special kind of solar charge controller. Where you need to be very careful is that some charge controllers need the battery connected before the solar panel - it is very easy to destroy this quite expensive item.
Solar panels that you carry on the bike need to be lightweight, and good ones are expensive.
Solar panels that stay at home or at work can be secondhand standard 250W or more panels, which can be cheap and perfectly good. These come up for sale when domestic systems are taken down, or solar farms upgrade. Think £50 or so for a 250W panel.