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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.
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.
Absolutely. I guess the low threshold for installation allows some kind of mass market economy of scale.
Great post! Thanks for doing the math and explaining the concepts!