[BurningFrog]

Tesla could offer an "attachment" to their cars that let them serve as a home battery when parked.

You'd have to let it charge up before going driving, but for home owners who don't drive much, that could be very cost effective.

Unless I'm missing some complication?

[thinkcontext]

Batteries have a limited number of charge/discharge cycles. If you use your car to power your home you'll have to replace the batteries that much sooner, at a cost of $thousands. Electric car buyers are paying a premium to have the batteries be mobile, better to use them for that application.