I was in another country when there was a power outage at home. My internet went down, the server restart but couldn't reconnect anymore because the optical network router also had some problems after the power outage. I could ask my folks to restart, and turn on off things but nothing more than that. So I couldn't reach my Nextcloud instance and other stuff. Maybe an uninterruptible power supply could have helped but the more I was thinking about it after just didn't really worth the hassle anymore. Add a UPS okay. But why not add a dual WAN failover router for extra security if the internet goes down again? etc. It's a bottomless pit (like most hobbies tbh)
Also (and that's a me problem maybe) I was using Tailscale but I'm more "paranoid" about it nowadays. Single point of failure service, US-only SSO login (MS, Github, Apple, Google), what if my Apple account gets locked if I redeem a gift card and I can't use Tailscale anymore? I still believe in self hosting but probably I want something even more "self" to the extremes.
This also makes self-hosting more viable, since our availability is constrained by internet provider rather than power.
Of course that means we’ll not have another ice storm in my lifetime. My neighbors should thank me.
A year later another atmospheric river hit and we had a 4 hour outage. No more jokes.
Make sure to run that generator once every few months with some load to keep it happy.
> maintain my familiarity with it in case I need to use it late at night in the dark with an ice storm breaking all the trees around us.
That's the way to do it. I usually did my trial runs during the day with light readily available but underestimated how much I needed to see what I am doing. Now there's a grounding plug and a flashlight in the "oh shit kit".
Assuming their heating, cooking and hot water is gas, a house doesn't actually consume that much. With a 50kWh battery you can draw just under 300W continuously for a week. I'd expect the average house to draw ~200W with lighting and a few electronics, with a lean towards the evenings for the lighting.
What follows is back of the napkin calculations, so please treat it as such and correct me if I am wrong.
1. Inverters are not 100% efficient. Let's assume 90%
2. Let's also assume that the user does not want to draw battery to 0 to not become stranded or have to do the "Honda generator in the trunk" trick. Extra 10%?
3. 300W continuous sounds a bit low even with gas appliances. Things like the fridge and furnace blower have spiky loads that push the daily average. Let's add 100W to the average load? I might be being too generous here, but I used 300W, not the 200W lower bound.
4. Vehicle side might need some consumption. If powering off the battery, it would probably need to cool the battery or keep some smarts on to make sure it does not drain or overheat? Genuinely not sure how to estimate this, let's neglect it for now.
Math is (50kw - 10%(inverter loss) - 10%(reserve)) / 0.4 = 100 (hours), ~ 4 days.
The above calculations assume a sane configuration (proper bidirectional wire, not suicide cord into 12v outlet). Quick skim of search for cars with bidirectional charging support for home shows batteries between ~40kWh(Leaf) to 250 kWh (Hummer).
So looks like one should be looking for ~80kWh battery, which actually most of the cars in the list have.
Again, very back of the napkin, would probably wanna add 20% margin of error.
Indeed with the fridge it pushes it a bit. But to address some of your other points:
> it would probably need to cool the battery
I'd expect if you're in a storm then you probably don't need any cooling - not to mention a 300W load is nothing for an EV battery compared to actually moving the vehicle. I'd expect some computers in the vehicle to be alive but that should be a ~10-20W draw.
On the other hand, my calculation assumes ~300W continuous. I expect the consumption to lean into the evenings due to the extra lighting, and drop off during other times.
But yes 80kWh might very well be what the OP has; I intentionally picked 50kWh as the lowest option I found on a "<major ev brand> battery kwh" search.