My idea was to use a 5-volt panel on top of the Tello to power it, and if the solar doesn't generate enough electricity it could get the rest from the battery. I have no soldering skills so i probably won't ever do it. just wanted to know if it could be possible
A lightweight 5w panel weigths around 200gr. Maybe you can strip & trim it to 150gr. Tello weights 80gr. There is no way Tello can lift a 5w panel.
Plus it doesn't produce enough power. Tello battery holds roughly 4wh and lasts 10 minutes. So it consumes around 24W. A 5W panel produces anywhere between 0W and maybe 4W since it is never exactly directed at the sun.
You could think about a solar powered charger for the battery, but as @volate!lo already mentioned: Even this charging process may take a significant amount of time.