"All of the above" plus one more. Integration with my home/campus PV solar system - and by this I mean both ways. I charge my Volt as a diversion load when there's extra electricity. (and am in the process of designing a new charger better adapted to do this automatically). But that's only half the story.
Anyone who runs on solar knows that it's not reasonable to design a system for that month of "dark" many of us get around February. Too many batteries, and their self-discharge is painful, too many panels and you're always letting electricity "fall on the floor" as your charge controller protects your house batteries from overcharging.
There are just those times when even the fairly expensive gasoline->electricity conversion is worth it, in terms of total cost of ownership of the systems.
Hardware store generators (or even the pro stuff they sell hospitals and phone companies) don't really meet my quality standards. The big ones running at light load aren't efficient, and of course, any of these need to be run fairly often to keep the oil on things, and to notice things that need proactive maintenance. Seems they always fail late on a weekend night in bad weather, when no parts are available as well. You can keep a couple so as to have hot spares, but that's not cheap, and then both have to be tested now and then - wasting gas.
Or, you can have a Volt in the driveway. It has a 16kwh battery (same as the house), or about half that maintained in mountain mode. You automatically drive the thing and keep it well maintained due to its use as a car. GM has made a very efficient generator in this thing, with IC engine tech miles and miles beyond even a fixed system UPS generator costing MORE than a Volt does. And oh -- it's many times more reliable than those are in actual practice.
So, you outfit the Volt with a way to put charge into your house/campus batteries - an inverter driving a battery charger will do that with the car on, and in mountain mode it will provide IC engine produced electricity if needed. My house needs quite a bit less than an auto - half a KW will easily maintain it, and the Volt is hip enough in design to simply cycle the IC engine as required to maintain that. It's a backup generator that can show you some fun while getting its own gas from the station - and you never spill any or get it on your hands like with a hardware store outfit.
Instantly doubling my house capacity even ignoring the IC engine, for something I'd have bought anyway - priceless.