Oh, I just realized I hadn't posted this. I was supposed to post this in December 2017.
Well, in December me and a friend, Katrin, took part in the Conrad Maker Faire.
We were doing a demonstration on how to charge a cell phone with a solar panel. We forgot that we needed the sun also for it to work out but we managed with a table lamp and a big solar panel.
It ended up being more like how to transfer energy for dummies. Which was also very helpful for ourselves because we didn't know anything about the subject before diving into the it.
So basically how to store energy from a solar panel to a battery and then from the battery to a cell phone battery. We could also demonstrate that you can transfer energy directly from the solar panel to the telephone but that is not exactly a best practice.
These are some pictures from our stand, which was also very DIY. Improvisation queens.