The “balcony” bit isn’t the defining characteristic, it shouldn’t be taken literally. Some people do have their “balcony solar power” on their roofs.
What defines it is limitation to 800 W and inverters that come with a normal Euro Type F (“Schuko”) plug and no legal requirement for professional installation. A layman can literally plug it in to an existing wall socket. Given that they are capped at 800 Watts, the inverters are also the simplest type and dirt cheap (although often they are literally just software-capped and identical to higher power ones, make of that what you will). Complete systems (2 panels, cabling, inverter) cost between 299€ and 800€ depending on quality. You genuinely only have to buy a fixture that suits your needs and a mate to help you install it.
Proper several-Kilowatt-systems are very expensive in Germany too.
I mean, the regulation seems to be, but there’s no fancy tech going on. I’m not an electrician but I think I can explain, as I have recently tried to understand myself. To understand why it’s possible it’s best to understand why the limit is at 800 W precisely.
So German wall outlets usually have a 16 A fuse and the wiring in the walls is dimensioned to accommodate slightly higher current (I think they are 2.5mm² gauge allowing up to 20 A but don’t quote me on that particular part) for safety reasons. I suppose it would be the same or very similar in Denmark, or maybe most of Europe that uses 230V/50Hz AC.
Now, normally, if you have dangerously powerful load that would melt your wires, let’s say 5 kW, and you plug it in to an outlet the fuse will just pop and you’re safe. If however you have a 2 kW PV system connected to a wall outlet nearby, it would theoretically be possible that your 5 kW load draws 13 A (3 kW) from the mains through the fuse and another 8.7 A (2 kW) from the PV system over the same wire in the wall that is only rated at 20 A but now carries 21.7 A. And the fuse would never pop at 13 A, making it a huge fire hazard. 800 W is basically just what will always comfortably fit into the safety margin of the wiring in German houses. All systems above 800 W need to be hardwired by professionals “behind” the fuse box so that every Amp from your PV goes through a typical 16 A fuse.
Absolutely. I guess the low threshold for installation allows some kind of mass market economy of scale whereas systems like yours are homeowners’ luxury goods.