There are a few ways to check whether you have three phase or not.

Open your switchboard and look for three black fuses.(see picture above).
Check your 'Main Switch' and see if it has three breakers.
Single phase would be just one switch.
You could ring Synergy and ask them.

Let me start with some basic rules relating to three phase solar in Western Australia.

15kW of solar inverter(s) is the maximum allowed.

You can install ANY three phase inverters in any combination so long as the total is 15kW or less...
BUT the inverters must be able to talk to each other so the required 1.5kW export limit is achieved.

You can install 3 x 5kW three or single phase inverters, with or without batteries.
Or 1 x 10kW three phase inverter plus 1 x 5kW three phase inverter, again, with or without batteries.
Or 1 x 10kW three phase inverter plus 1 x 5kW single phase inverter with a DC coupled battery.
Or 1 x 15kW three phase inverter with or without a battery.
Or 1, 2 or 3, 5kW single phase inverters with DC Coupled batteries on each.

If you exceed 5kW then...
(1) You must purchase the inverter consumption meter (typically $500-$700 installed).
This meter will then be used to restrict your solar exports across all three phases combined, to no more than 1.5kW
(2) You will not be paid anything for your surplus solar anyway.

How solar 3 phase inverters work
These inverters are constantly 'Exchanging power with the grid' at the meter.
When you get solar you must also get a bi-directional 'net meter' installed (by Western Power in Perth.)
Without these meters, three phase inverters wouldn't save you much money. They are crucial.

Whatever solar power is extracted from the panels is converted into AC by the inverter.
That power is distributed evenly across all three phases.
It's called 'Balanced Output'.
So if 6kW was produced then the inverter would distribute 2kW on each phase.

Let's say you are charging your EV on Phase A at 7kW.
Let's also say that your fridge, freezer, lights etc are drawing 1kW on each of the other two phases.
So your home is using 9kW of power and your solar is producing 6kW
You are importing 3kW from the grid at that moment in time.

What happens is so entirely dependent on the Western Power's meter to 'Net' the imports and exports.

Your EV receives 2kW of solar power on phase A and imports the balance, 5kW, from the grid.
You have a surplus of 1kW on the other two phases, so 2kW in total of exports.
The meter 'nets' that out so you only pay for 3kW.

All 3 phase solar inverters work this way
If it's a 5kW three phase inverter then it can't deliver more than 1.667kW per phase.
A 10kW three phase inverter, no more than 3.33kW per phase.

You may come across claims that some inverters offer 'unbalanced output'.
They say the inverter will output different amounts of power on each phase, as required.
What they don't say very clearly is that the 1/3rd of inverter capacity per phase rule still applies.
e.g., you can't have any 10kW inverter, balanced or not, deliver more than 3.33kW on any one phase.

In Australia, with our bi-directional 'net' meter the 'unbalanced output' feature is irrelevant.
The picture below shows why. On the left, 'Unbalanced', on the right, 'Balanced'
Same solar production, same loads, same 1.7kW import from the grid.
That's entirely because in Australia we have bi-directional 'net' meters when you install solar.




How does export limiting work with 3 phase inverters.
New installs in WA over 5kW need to be export limited to a maximum of 1.5kW across all phases.
In other places in Australia, it can be zero export.
It makes no difference to a three phase inverter and a bi-directional net electricity meter.
Exchanging power with the grid at the meter goes on as normal, but the inverter will control what it pulls from the panels
as additional export.

Adding extra inverter(s) and panels to an existing 3 phase installation.
Let's say you have a 3 phase 5kW Fronius Symo inverter and 6kW of panels and you now want to go big.
There are EVs to be charged, big A/C unit as climate change makes your house hotter, etc.
Western Power here in our home town of Perth will, in most cases allow you to add another 10kW of inverter(s) and associated panels.
But...you have to be export limited and that means all your inverters need to talk with each other and that almost always means...
Getting the same brand of inverter with your new inverter(s) as your existing, or chucking the old one out and starting over with another brand.

I discuss this subject with half a dozen people every week.

What three phase solar inverters are currently available in Australia?
Fronius, Huawei, Sungrow (my three favourites and all with battery capable models)
Next best, Goodwe/GE, SolarEdge and SMA.
Others... Growatt, Solis, SolaX.

Can I connect single phase inverters to three phase in Perth?
You can.
Western Power won't allow a 5kW single phase inverter on 3 phase unless it has a battery connected.
If you want 2 x 5kW single phase inverters then both must have a battery connected.
If you want 3 x 5kW inverters then that's fine with or without a battery because it's 'balanced'.
You can also have a 3kW inverter on it's own, or a 3kW and a 2kW, or if you can find them, 2 x 2.5kW

How do single phase inverters work on 3 phase?
They work in the same way as described above with three phase inverters.
They are constantly exchanging power with the grid at the meter.

Let me allow Western Power to explain it their way....

The Western Power (WA) Rules

"The 3 phase meter measures the combined consumption and

generation across all three phases continuously - it does not distinguish

between phases and then takes the net after a set period (of 10 minutes).

If there is excess generation on one phase, and a load on another phase,

then the excess generation will supply that load. If there is still more power

required, then the customer will receive electricity from the network and it

will be recorded in the meter as purchased/imported electricity. But if

there is still excess generation after supplying all of the household load,

it will be sent out onto the network and recorded as sent out (or exported

onto the network), which is where the customer receives REBS and/or FiT

(or neither if they aren't eligible)."