You can also just do balcony solar and tell them to get fucked. Legal issues only come from connecting it to the mains, if you connect it to a battery its just a camping solar/battery setup instead and totally fine. You could also charge the battery from the mains when there is no sun.

Considered it, but energy is cheap and stable enough it doesn't really seem worth the effort. USB power banks are alright, I suspect they sell higher volumes so mass production makes the cost/Wh more competitive.

Now if I had an off grid cabin, suddenly all sorts of fun solar/battery options exist.