I have friends in Hawaii with grid-tied solar, and that essentially makes their house net-positive. They get enough over-production to cover their grid usage and charge an electric car (same as he other commenter with a volt, they charge a bit at work too). No heating (no insulation), and they get by with ceiling fans and no A/C--house design is all about post-and-pier and airflow, not thermal mass. Hot water is solar too, with electrical backup. I guess they do use a bit of gas for cooking, I'll have to ask about that. As you can imagine, it's easierto be net-zero or net-positive there with the mild weather.
One thing I've done myself is to add a small solar array and batteries to my regular house. This is not grid-tied, it's a separate 12 VDC system. this is only for lights, all appliances still run off of the 110 AC. I installed cable lighting with 12 VDC LEDs in all my house, so I have really bright lights, like halogen, without the incandescent heat or CFL colors and flicker. I had an electrician install the inverter and wire the batteries, then I ran my own cables through the attic, down to some DC switches, and strung the lights. I also added some 12-to-5 VDC USBcharging ports for phones and tablets. It saves a bit of electricity, though not enough to be really be cost effective because batteries are expensive (but not insanely expensive because ey are not sized to run a fridge or a well pump). But in the end, I also have nicer lighting and backup for storm outages, etc.
