Earlier quoted context omitted.
A powerwall has what, 12ish KW usable (less in reality) which a single one can power a house for for up to a day if you're careful about what you're using. If you scale that up to the 75KW+ batteries being put into EVs today buying an inverter could be a good investment if you live in an area with frequent power outages (or a cabin or whatnot). There was also some talk about Teslas being able to send power back to th…
AFAIK there are other makers that are also ready for this. I seem to remember that the Leaf is. What I think will be the hard part of including cars into the grid is the warranty issues. I.e. if a battery gets so much usage from the grid that it somehow gets broken or worn out, who should take that cost/ risk?
I've heard the hard part right now is more regulatory in nature. Especially in the US where energy regulations vary not just from state to state, but also sometimes regionally within states based on power utility provider for a region.