Wild. I wonder how they deal with the back feeding issue. Is there something about the home wiring in those countries that prevents it? (or do they just not care and line workers know to check if a line is truly dead?)
(At least, this is what electricians working with 33kV in industry in Europe do, e.g. if doing maintenance on a cable to a datacentre.)
A manual break-before-make transfer switch will do the job. Not much help if you’re not home and the mains goes out and your food spoils, though fridges will stay cold for hours if left shut, and longer if there’s a lot of thermal mass in them - try to keep most of the empty space in your fridge and freezer filled with water bottles.
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.