I just finished installing my own 6.6kW system. From my research, we're not at the point yet where an inverter that can be (a) grid-tied and (b) charging batteries will be as reliable as one that does either (a) or (b) (but not both).
They do exist, however, and hopefull they will get better over time. This will allow more people to add a moderately sized battery system to a grid-tied system, and then we end up with the best of all possible worlds (or something much closer to it).
There are also grid-tied inverters that will provide limited online power even with the grid down. These also seem to be not as reliable as the "grid down? i'm down" design.
The really tricky part is that for the inverter's output to be instantly switchable with the grid, it has to be phase aligned with it, and so the inverter has to see the grid phase and match it.
They do exist, however, and hopefull they will get better over time. This will allow more people to add a moderately sized battery system to a grid-tied system, and then we end up with the best of all possible worlds (or something much closer to it).
There are also grid-tied inverters that will provide limited online power even with the grid down. These also seem to be not as reliable as the "grid down? i'm down" design.
The really tricky part is that for the inverter's output to be instantly switchable with the grid, it has to be phase aligned with it, and so the inverter has to see the grid phase and match it.