Single-phase off-grid inverter on a property with 3-phase grid — how would you approach this?
We’re currently designing a somewhat unusual residential solar project and I’d like to hear from installers/electricians who have dealt with something similar.
The property has a 3-phase grid connection.
Planned system:
- Around 6–8 kW of PV
- Around 15–20 kWh battery storage
- Maximum load we expect the inverter to supply is around 8 kW
The important part is that we do not need grid export.
The idea is basically a backup/off-grid style system:
When the grid is available, the house can use grid power and the batteries/solar system normally. If the grid fails, we want the inverter + batteries + PV to supply the necessary loads.
Because we don't need export, using a full 3-phase hybrid inverter seems unnecessarily expensive. We have access to much more cost-effective single-phase off-grid inverters, but the building itself has a 3-phase supply.
We don't yet have the exact L1/L2/L3 load distribution, but the total backup load should stay below approximately 8 kW.
So my main question is:
How do you normally integrate a single-phase off-grid inverter into an installation that has a 3-phase grid connection?
I'm NOT talking about using three single-phase inverters in parallel to create a 3-phase system. I'm specifically interested in using one single-phase inverter.
Would you:
- move all essential/backup loads onto one phase?
- create a separate backup subpanel supplied by the inverter?
- reorganize the existing loads between phases?
- use some other transfer/changeover configuration?
And what happens if the property has actual 3-phase loads rather than just single-phase loads distributed across L1/L2/L3?
I'd especially appreciate hearing from anyone who has actually installed a system like this. I'm interested in real-world practices, limitations and things we should be careful about.