In this one, it's all in the inverter. You just plug it into an outlet, and it can do up to 1000W (though 950 was the most I've ever gotten from 1.2 KW of PV coming in at ~90 volts).

You can have multiple inverters; they match the frequency and voltage of the incoming utility power and won't output anything if there's no utility power coming in (anti-islanding protection).

The only thing to be aware of is not over loading a circuit where you have them connected. I do have a dedicated circuit/outlet for that.

They're useless if the power's out, but I'm looking into something of a transfer switch to redirect the PV output from the grid-tie inverter to a regular one, but I haven't gone too far down that path yet.

Edit: It's the same principle that's used in balcony solar