alt Hacker Newsit is actually simpler. The inverter stops power flow if it does not detect a grid voltage.
The actual power coming from a balcony setup is tiny, a thousand watts ballpark. The typical house will consume the vast majority of that capacity.
Even if some flows back to the grid, it will likely be consumed by losses in the transformer and wires.
You’d be surprised how few watts a fridge and a TV draw, 500 watts combined, and that’s only while the compressor in the fridge is running. Don’t open the fridge very often, or keep a lot of thermal mass in the form of filled water bottles in there, and the compressor in a fridge will spend most its time not running.