Germans Combat Climate Change From Their Balconies: Plug-and-play solar panels are popping up in yards and on balcony railings across Germany, driven by bargain prices and looser regulations.

I'm not thinking the main circuit breaker or the meter.

Were I live appartments have a whole board of smaller circuit breakers once for a different circuits inside the appartment - for example there might be a circuit just for illumination, another for kitchen wall plugs, a different for bedroom wall plugs and so on, and for each of these there will be one such small circuit breaker.

These small circuit breakers normally have a lower trigger point than the main circuit breaker, though they might be different depending on the circuit since different kinds of things draw different amounts of power - i.e. household lamps aren't going to be drawing 1000W whilst an electric oven or electric heater might very draw that or more power.

In a normal situation, the current comes from the outside, through the meter and the main circuit breaker and then gets divided based on demand and goes through each smaller circuit breaker and feeds whatever is drawing power in those circuits.

If you have a balcony plug-in solar power system there, wired to any circuit, IF the power does come OUT from that circuit (I'm not sure, though it makes sense it can) and into the other circuits, then wouldn't the trigger point of the circuit breaker for that circuit (which as I said is lower than the main circuit breaker's) be important?

If I remember it correctly circuit breakers are electromechanic and don't really care which direction the current is going (so OUT or IN is all the same) just how much of it is passing through, so the current going OUT instead of IN on one of those circuit breakers would be fine, but even that being the case, it might still be a problem to wire the solar power via the circuit for the illumination rather than the circuit for the wall socked because the circuit breaker for the illumination circuit might have a lower trigger point than that for the wall sockets circuit (because you might connect a 1000W device to a wall socket whilst a 1000W lamp was already insanelly powerful back in the Filament Lamp days and is much more so in the LED Lamp days).

PS: Your point about "will power come out of my household and how does that interact with the meter and the main circuit breaker" is also important, but I wasn't even thinking about that since I was thinking about just the difference between wiring the power out from an appartment balcony via the circuit for the outside lighting vs bringing that power inside the dwelling and connecting it to a wall socket and hence a different circuit.