alt Hacker NewsIIUC plug-in balcony solar is subtly different. It's basically aimed at grid-tie operation, connected by backfeeding through a standard 120V 15/20A branch circuit. On its own that's unsafe as you could have downstream loads drawing more than the 15/20A circuit ampacity, but I think the idea is still at the pinky-swear-it's-a-dedicated-receptacle-and-cross-your-fingers stage.
The units likely have "protected outlets" too that likely use an internal transfer relay to disconnect from the grid side, but at 15/20A it doesn't have to be terribly beefy.
Yes, they're an interesting little loophole device. They are likely not going to be legal in the long run because of the overload potential, even though in practice you'd have to work at that to make it happen. After all, these are typically no more than 300 to 500 W and angled in a very unfortunate way so likely not making full power. The wiring connecting them to the distribution panel is not going to sweat handling - again, potentially - that much more power over the 16A typical limit, that's just 2A more and you are more than likely not going to have that much consumption going on on that same circuit.
I have a similar situation here but at much higher power levels, a single underground cable from my garage to the house carrying 16A tri-phase and a whole raft of consumers in the garage itself. There too there is the potential for overload with both consumers and producers on the same cable. The solution there was to have a secondary distribution panel, breakers on both sides of the cables, for the consumers and for the inverter guaranteeing that none of the wiring in the panel or to the house or the consumers ever exceeds its rating.
This was by far the most cost effective solution, saved adding another ground cable and relieves the main distribution panel of a lot of current going in and out of the garage.