That's not what this. This is plugging straight into the wall with a small system. Against code pretty much everywhere. What you're talking about is only economically viable for large systems that will generate more than the owner can use at peak hours. These small systems are much cheaper, do not require an electrician, and won't generate enough power to require a net metering setup. The owner will use all of the power it generates even at peak hours. It essentially will just slow their power meter down as they draw less from the grid. These small systems are very common in Europe these days because their regulations have kept up better than ours. Also their outlets in general are safer.

Obviously where this person is that's legal, so there are exceptions. I assumed this setup involved a battery because they grossly overpaid for a 400 watt system.