Yeah that's likely not allowed, or really doable. Anything beyond a simple plug-in battery requires a licensed installer. There are some small capacity batteries that aren't that expensive, you just need the room for it.

A lot of houses here are terraced, so actual room for a powerwall is very limited. You usually only have a few meters of front and back exterior walls, with big windows. And any apartment owner is going to have to fight with the HoA to install something.

Not saying it's impossible for all houses. But I was replying to the "why don't we cover all buildings with solar" sentiment.