One of the biggest problems with using solar and wind energy for the grid is that storing vast amounts of energy is expensive and, as of yet, seen by most as impractical at the scale requisite for allowing solar and wind to provide energy on a scalable reliable basis without fossil fuel capacity to use as back for when it is dark/not windy.
According the US EIA:
"In 2012, the average annual electricity consumption for a U.S. residential utility customer was 10,837 kWh, an average of 903 kilowatthours (kWh) per month. Louisiana had the highest annual consumption at 15,046 kWh and Maine the lowest at 6,367 kWh."
So dividing the monthly average of 903 kWh by 30 days, we get an average consumption rate of about 30kWh per day. Whereas the lowest capacity Model S has a battery that carries 60 kWh. So compared to household needs, this is an enormous potential source of energy storage.
If, per instance, a nearby supercharging station utilized renewable sources, then you could charge up your transportation and household simultaneously, quickly, and, with a Tesla, for free. Couple this with grid sources for most of the day, and you could use the car battery to power your house at night.
Nissan has built a device enabling this functionality for the leaf that costs (without subsidy)$6,000. Common estimates for the cost of the Tesla battery place it as most likely above $20,000.
This would lessen the life of the battery. Per a 200 mile range for 60 kWh, 30 kWh is the equivalent of 100 miles or half a charge/discharge cycle (much less than that if you only use it at night). Still it seems like a great idea, if not immediately for everyone, then perhaps some time not too far off.
I think the key take away here is that, supposing a significant commute, cars and houses use similar amounts of energy per day - so it isn't far fetched to suppose that a solution to renewable energy storage for cars could also serve household needs.
Is Tesla looking at this much? I've read they included it with the roadster: