Solar and 3 phase power

 

 

Approximately 20% of Australian homes have a 3 phase supply. What that means is that four wires run into the property not two, and the meter is a 3 phase meter. You may not run any three phase appliances (typically bores and large reverse cycle AirCon) but if you have a three phase meter, then you are lucky in some ways and unlucky in others as far as solar is concerned.

Lucky?
You are allowed in most locations up to 10kW of solar inverter(s) per phase

Unlucky?

It often costs more.

Connecting inverters to 3 phase

Most inverter manufacturers have three phase inverters, although very few currently have any 3 phase hybrid inverters (ones that can connect batteries directly to them).

Network operators prefer you to connect a 3 phase inverter (or several of them) if you have 3 phase supply but connecting one or multiple single phase inverters is usually fine too.

Recommended 3 phase inverters

Fronius Symo range from 3kVA to 20kVA

SMA Tripower range from 5kVA to 25kVA

Huawei Fusion range from 8kVA to 33kVA

ABB Trio range from 5kVA to 50kVA

Goodwe range from 5kVA to 25kVA

Connecting batteries

None of the above are hybrid inverters and therefore batteries can only be connected via an additional AC or DC coupled interface. See this FAQ

Fronius Symo also comes in a 5kVA hybrid version. Single MPPT (1 roof orientation, or two equal sized orientations only) but can only connect its own excellent but hugely expensive battery since the demise of Tesla Powerwall Version 1.

Connecting single phase inverters to 3 phase

Very common practice and solves the battery issue as most hybrid inverters are single phase (Huawei have a 5kVA 3 phase hybrid coming out later this year and SolaX have a 5kVA to 10kVA range of 3 phase hybrids now...but very expensive)

If often leaves people a bit puzzled as to how one or two single phase inverters connected to a house with 3 phases can work so here is how...

Let's imagine a house with lights and oven on phase 1, air con on phase 2 and power outlets on phase 3. The electrican who wired the house would have usually tried to predict and balance the 'loads' evenly across the phases.

In this hypothetical example, the solar installer has put a single phase inverter on phase 3.

All of the solar power flows around in a circuit on that phase and provides power where required with any excess flowing to the electricity meter. The demand for power from phase 1 and 2 is provided entirely from the mains supply not the solar. Sounds really bad doesn't it? Going to lose out with solar being exported for peanuts?

No. The "secret" to understanding all of this is the electricity meter. It couldn't care less what power you use on each phase, it just adds up ALL the power you've used on all three phases combined, and typically it does that every ten minutes, and deducts all the excess solar it has received. We have included the official description in red from one of the electricty distributors (Western Power) at the bottom of this page.

Mathematically it might look like this...in a ten minute period.

(Solar produces 0.8kWh)

Phase 1 (Lights and Oven) 0.2kWh

Phase 2 (A/C) 0 kWh

Phase 3 ( Power outlets) 0.4kWh

Meter calculates

Total drawn across all phases = 0.6kWh

Total received (from solar) = 0.8kWh

Issue customer with credit for 0.2kWh exported back into the grid

Rules

Each electricity company has their own rules as to what they will allow their customers to connect on their network.

As far as three phase inverters go, they can be added up to 30kW in almost every area.

Using single phase inverters is almost always limited to 5kW per phase, although some companies like AusNet in Victoria limit it to 4.6kW per phase, and in WA it's only 3kW per phase which is why we often install a 3kVA and a 2kVA single phase inverter (or two 2.5kVA) in WA.

 

The Western Power (WA) Rules

This is how Western Power officially describes how their meter works...

"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)."