floitsch parent
Balcony solar requires the 50Hz of the energy grid. If you turn off the main power they will stop feeding into the system.
So if enough of your neighbors have these panels then the grid never gets turned off.
Technically probably yes, provided you had millions of neighbors, the sun never sets and all big users like kettles and heat pumps kindly switch off as well. If either of those conditions stops being true, then either the frequency or the voltage will drop too much and the panels turn themselves off. In practice these balcony panels are not sufficient in the slightest to power a house, let alone an entire apartment building, and they will turn off almost instantly.