@Bullitt : as mentioned above by AmpLee (I think of Rush fame?) There are a couple of choices when you're using the Sol-Ark in Grid Tie. If you you only use the 'Grid' In/Out of the Sol-Ark, you won't get 'off-grid' power at all if the Grid goes down. You'll tie the Sol-Ark 'GRID' in/out directly to your utility mains right after your meter. If you don't care about that, like your Grid is reliable, then maybe you don't need that. You'll be able to shift your grid power usage to non-peak cost times with little effort, you'll just have to program the Sol-Ark's time of use function to make sure the batteries can supply power when there isn't enough PV available to power your loads.
If you want to be able to be able to use the Sol-Ark PV and Batteries to power your house loads if the grid goes down, you'll have to connect the Sol-Ark's LOAD output. As a grid-tie inverter, the Sol-Ark will not attempt to draw or send power at all if it senses there is no power from the grid. Then the simplest solution is to have a Critical loads panel directly connected to the the LOAD output. In the event of a power outage you'll get a seamless transition from Grid +Solark power to just Sol-Ark "LOAD" output power. However, in non outrage situations you'll be limited around 12KW of total power available to the critical loads panel. This might not be enough to power all your stuff at once and it adds complexity to your system, because you'll have to add another circuit breaker panel to your system for either the critical loads or the non critical loads.
If you don't need the 'seamless' transition from on Grid to off grid, then, as Amp Lee said, you could put in a 'transfer switch'. This ensures that you can still have your house powered if the utility grid is down. You'll have to connect this switch in between your Sol-Ark "LOAD" output and your Circuit breaker panel. It will interrupt the utility power and switch your breaker panel to use the Sol-Ark's LOAD output. It's not seamless. Your home will be without power for a time from when the grid goes out and you switch the transfer switch.
The transfer switch ensures that you Sol-Ark's "LOAD" output is never connected to the utility and/or the Sol-Ark GRID in/out. It is potentially bad for your Sol-Ark if this happens, and could be dangerous for utility workers working on power lines they think are dead. There are tons of transfer switches out there, including some that are built into breaker panels, usually meant for generators, but can be used for the Sol-Ark's LOAD output. They include a mechanical interlock, which physically prevents the 2 sources of power to be connected together at the same time.
If money and time/complexity is no object, then paralleling multiple Sol-Arks is probably the most elegant solution. You just never have the Grid directly connected to your house breaker panel. You'll have up to 24K(or more depending on how many So-Arks you have) to power your loads at once during a utility outage, and if there is a outage, and you have enough PV/battery power, the transition to 'off grid' will be seamless. You'll also be able to add more PV to your system, which is an added benefit.
One caveat of paralleling multiple Sol-Ark's is that each Sol-Ark can only produce about 4500 watts of power per phase of the 240V split phase 120v. If your loads are unbalanced, ie if you power on 120V devices on one phase / leg that total more than 4500W, then the Sol-Ark will overload and shut down. The paralleling of Sol-Ark's uses a communication channel between them but the load balancing is not perfect or instantaneous. Your unbalanced loads may peak above 4500 for a short time but will trip your Sol-Ark and it will shut down. A properly wired 'autotransformer' can help with unbalanced loads to keep this from happening, even when using a single Sol-Ark.
Hope this all helps.