There are all sorts of issues with using a regular grid-tied inverter in an off-grid situation; there are regulatory issues besides the anti-islanding (which is a complicated topic all on its own), and technical challenges too. A lot of the technical challenges go back to the inverter effectively being a thing that bolts on to the existing house wiring; I think that if they could be more of a pass-through thing (like a UPS) then the picture would be a lot simpler.
An off-grid capable inverter needs to handle several state transitions smoothly, and some of those are hard. For instance, starting up can be a lot harder when there's no mains voltage. An inverter will have a maximum output current, which is generally not too far from the maximum power output of the inverter divided by minimum mains voltage. If you have a load that presents as a constant resistance, like a water heater, then as the inverter's output voltage goes from 0 to 240V (120V for areas with weenie power) the current will smoothly go from nothing up to whatever the load normally draws, along with the voltage, and there's no problem. But! A lot of loads aren't resistive - things like computers, battery chargers, and inverter-driven motors (as newer appliances often have) will tend to look more like constant-power loads. So, once they decide it's OK to turn on, if the voltage happens to be half of nominal at that point, they will try to pull twice their nominal current. If that causes the total draw to exceed what the inverter can provide, it stops and maybe tries again. It's practically impossible to measure what the load characteristic of something like a house, from the perspective of an inverter, so the best you can do is something like guess-and-check, and that's not a great solution.
Then, how to handle reconnection with the grid; you either need to re-synchronise before reconnecting, or ensure that the intrepid homeowner first shuts off the house before turning the switch to reconnect.
Switches that can handle that job may need to be specified per-installation, and there are all sorts of regulations around how they work and where they can go. They are not cheap, as a rule. Some regions have the solar generation stuff on a separate export power meter from the import one. This means that the switch needs to be on he supply side of both meters, and that could be regulatorily complicated.
What about multiple inverters? These things all need to play nice with each other when solo, or installed with others. Perhaps you didn't design those, and they might try to start up too, then fire up their anti islanding which should promptly trip out again.
Remember this all has to work with variable input power available, and it needs to be packaged up so that installation is straightforward, and operation is basically hands-off. Oh, and inexpensive too!
An off-grid capable inverter needs to handle several state transitions smoothly, and some of those are hard. For instance, starting up can be a lot harder when there's no mains voltage. An inverter will have a maximum output current, which is generally not too far from the maximum power output of the inverter divided by minimum mains voltage. If you have a load that presents as a constant resistance, like a water heater, then as the inverter's output voltage goes from 0 to 240V (120V for areas with weenie power) the current will smoothly go from nothing up to whatever the load normally draws, along with the voltage, and there's no problem. But! A lot of loads aren't resistive - things like computers, battery chargers, and inverter-driven motors (as newer appliances often have) will tend to look more like constant-power loads. So, once they decide it's OK to turn on, if the voltage happens to be half of nominal at that point, they will try to pull twice their nominal current. If that causes the total draw to exceed what the inverter can provide, it stops and maybe tries again. It's practically impossible to measure what the load characteristic of something like a house, from the perspective of an inverter, so the best you can do is something like guess-and-check, and that's not a great solution.
Then, how to handle reconnection with the grid; you either need to re-synchronise before reconnecting, or ensure that the intrepid homeowner first shuts off the house before turning the switch to reconnect.
Switches that can handle that job may need to be specified per-installation, and there are all sorts of regulations around how they work and where they can go. They are not cheap, as a rule. Some regions have the solar generation stuff on a separate export power meter from the import one. This means that the switch needs to be on he supply side of both meters, and that could be regulatorily complicated.
What about multiple inverters? These things all need to play nice with each other when solo, or installed with others. Perhaps you didn't design those, and they might try to start up too, then fire up their anti islanding which should promptly trip out again.
Remember this all has to work with variable input power available, and it needs to be packaged up so that installation is straightforward, and operation is basically hands-off. Oh, and inexpensive too!