How do you connect SMA Sunny Island to a 240V three phase service panel?

Truesolar,

I think you entered a typo in your title: Did you mean to say 3-phase?

If so, then you probably have 208/120 3-phase. The SI4248-US has a single-phase output of 120V at 60Hz. Two inverters can be "stacked" to provide 120/240V 60Hz split-phase output. You can connect up to four SI4248-US inverters in series/parallel for up to 16kW at 120/240V 60Hz. Or, use three inverters for 12kW at 120/208VAC three-phase power.

It's most likely that you have 120/240 split phase power - like most houses in the US. If that's the case then you have two choices:

1. Buy two SI4248s and stack them in Parallel to run your panel and keep the Solar inverter going.
2. Buy an Autotransformer (a good one of 5kW is about $500) and place it between your PV Inverter - connected to a split phase protected loads panel - and the Sunny Island.

In fact, these are your only options if you are using any SMA inverter larger than the SB 700 (700W). All other SMA inverters output 240VAC or more.

If you go with the SMA SB 700 then you will have 4kW of battery power x however many Ah your battery bank is - but recharging at 700W max (unless you install more than 1 SB 700)... 

You may want to think about what your critical loads are in the event of a power failure (do you have 240VAC pumps that you have to run?) then design the smallest possible critical loads panel around that need - you'll save money and extend the reserve power of your battery bank.