I live in the SF Bay Area, where the utility company, PG&E, has decided to start shutting off the power for days at a time when they feel like it.
I've got 7kW of solar panels on the roof, and a 64 kWh battery in the car in the garage, which is all the pieces I'd need to be able to ride out an outage indefinitely (as long as the car was home), they just can't work together to do that. I'm wondering if I can come up with some kind of home brew partial solution to this problem. Even if I can't use the solar panels, I'm thinking I could use a third-party inverter to run my refrigerator off of the car battery. Has anyone tried something like this?
My main concern is that unless there's some way to connect directly to the high-voltage battery, I'd probably need to connect via the 12v battery. What's the capacity of the system that recharges the 12v battery from the main battery?
I share your interest in this, but ...
What many people don't realize about backup power systems is that they need to guarantee that they don't backfeed into the grid during a power outage. This is a legal requirement, and its primary purpose is to prevent your backup power from electrocuting some poor power-company lineman who is trying to repair the grid and thinking that it's de-energized because they've switched off the feed from the power company end.
For this reason, most PV installations (including mine) use an inverter that automatically shuts down when it doesn't sense electrical power from the distribution grid.
There's a simple model to do what you want to do (but it doesn't involve your car battery). You purchase a portable, gas powered generator. When the power goes out you wheel it outside, put some gas in it (or hook it up to a natural gas supply line if it's designed to run on natural gas), and run a long extension cord into your house to run the refrigerator, maybe your wifi and a phone charger, but not much else. You can do this for maybe $300 - $500.
There's a more complicated model (and it still doesn't use your car battery): You hire an electrician to install a generator outlet and generator switch. You purchase a (possibly larger) gas powered generator. When the power goes out, you wheel it outside, provide it with fuel, and connect a special cord to the generator outlet that the electrician installed. You flip the generator switch, which physically disconnects your house wiring from the grid, and simultaneously connects your house wiring to the generator outlet. Now your whole house is running on generator power, legally. You can probably do this for about $1200, if you find a reasonable electrician.
The fuel part is kind of a challenge: when the electricity goes out, the gas stations can't usually pump gas. So you need to store a few gallons of gas, and you need to replace it every few months or put fuel stabilizer in it to keep it from going bad while it's sitting around in a gas can. And storing it has its own set of concerns.
There's a "Mickey Mouse model": you can purchase a 120 volt inverter that will plug into the 12V power outlet on the car. That would be capable of running something like a wifi router, but plugging even something as small as a crock pot into it might be too much power draw. The higher end Niro trim packages have a 120 V inverter built in, but I think the same power draw limits apply: maybe you can pump up an air mattress or run a router, but I think mine still won't run my crock pot.
If you want to substitute your car battery for the gas generator in either the simple model or the more complicated model, you need to find an inverter that can deliver higher current loads and you also need a safe way to connect it to the battery without electrocuting yourself. And then you're either stuck with the simple model's limitations (anything you run has to be plugged into an extension cord) or the more complicated model's requirements (need a generator switch and a generator outlet and a generator cord).
It drives me crazy to think that I have a PV system on the roof that generates more electricity than I use in a day (most of the time), but if the grid goes down, I can't use any of it. But when I look at what it would take to be able to use that in a power outage, it's up around $10,000 to install something like a Tesla Powerwall and all of the additional switching technology. Compared to a gas generator and a small amount of electrician work, it's about 10 times more expensive to install the Powerwall.
If you find a solution that strikes a happy medium, I'd love to hear it.
If you go the generator route, be aware that the less expensive high power ones can be really loud.