It's just a matter of buying the right equipment. If you buy the wrong inverter, it just switches off when the grid goes out. You need some device that detects that and can disconnect from the grid (to prevent power going out to the grid) and then power the house. This is called islanding. Not all inverters support this. The ones that don't will switch off when the grid goes out. In addition to that, you might need a physical switch or transferring device that takes care of making sure no power leaks to the grid in case of an outage. Setups without this require inverters with anti-islanding that will switch off if the grid power drops.
Outages are rare enough here in Germany that few people go the extra effort and cost to install the necessary equipment. But with the right equipment (which is available if you go look for it), you can definitely get this installed. In places like Australia, outages are more common and it's generally not that costly to upgrade your setup to support proper islanding and it's more common for people to design their systems for this.
Of course people if feel compelled to prepare for WW III that might be a good motivation. On the other hand, we'll have bigger issues if it comes to that.
Alternatively, you can get a plug-in battery with solar input and AC outlet for pretty cheap. In normal times, the battery is only connected to an AC socket, and tries to balance out my daily usage (includes a power usage monitoring device in the breaker box).
If/when the fan is hit with brown stuff, I can plug a few of my solar panels into the battery directly (they are now wired to my basic inverter without island mode), and then I still have some backup power.
It is not a solution for everyone, but redoing all my electricity hook-up, getting a whole-house battery and a three phase backup option would easily cost 20k. And it would cost a tonne of space, cause all this battery and inverter stuff needs to be close to the main connection (where I don't have space). The solution I chose was only 1200 for a 2kWh battery with built in inverter for 4 panels. And the battery is actually portable, I could technically use it for camping. Output is limited to 1200W AC from battery, or 2000W AC when there is enough solar input. To me spending 1200 Euro to have some electricity in case of WW III (or some significant sabotage) felt worthwhile
Outages are rare enough here in Germany that few people go the extra effort and cost to install the necessary equipment. But with the right equipment (which is available if you go look for it), you can definitely get this installed. In places like Australia, outages are more common and it's generally not that costly to upgrade your setup to support proper islanding and it's more common for people to design their systems for this.
Of course people if feel compelled to prepare for WW III that might be a good motivation. On the other hand, we'll have bigger issues if it comes to that.