I had no idea that is possible??? Is that special for Germany?

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 it as well.

So German wall outlets usually have a 16 A fuse and the wiring in the walls is dimensioned for safety reasons 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). 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 13A. A fire hazard. The number of 800 Watts is basically just what will always comfortably fit into the safety margin of the wiring in German houses. All higher power systems need to be hardwired by professionals “behind” the fuse box so that every Amp goes through the normal 16 A fuse.

still such an 800W system is dirt cheap by comparison

Absolutely. I guess the low threshold for installation allows some kind of mass market economy of scale.

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.

His fanatic supporters do, but the meme is referring to “casual voters”, so I guess braindead people who think they aren’t very politically inclined at all and are talking about the economy or gas prices when justifying voting for Trump.