Three-phase or single-phase: what it means for your system

The most common reason a quote comes back smaller than expected is not your roof. It is your electricity supply.

The short version

Single-phase supply gives one active conductor. Most established Australian housing has it. For solar, distributors generally allow around a 5 kW inverter without a difficult approval — which is where the ubiquitous 6.6 kW package comes from, since panels can be oversized against the inverter by up to a third.

Three-phase supply gives three. It is common in the newer growth-corridor estates, in larger homes and in anything commercial. It supports substantially larger inverters, and the export is spread across three conductors rather than concentrated on one.

Why the limit exists

Exporting power pushes voltage up at your connection point. Too much export in one part of the network and voltage rises beyond the allowed range, which causes inverters to trip off and can damage equipment.

Distributors manage this by limiting how much any one customer can export. Because three-phase spreads that export across three conductors, the ceiling is proportionally higher.

This is also why a system size that is routine in one suburb needs a separate application in another — it depends on your distributor and the state of the local network.

How to tell what you have

Look at your switchboard. The main switch is the clearest indicator: a single-phase main switch is one module wide, a three-phase main switch is three modules wide and operates as one block.

You can also count the active conductors at the meter, though that is harder to read on modern enclosures.

If you are unsure, your electricity retailer can tell you from your NMI, and we check it as part of quoting anyway.

In practice, by suburb

In the established northern suburbs — Reservoir, Thomastown, Lalor — single-phase is the norm and a 6.6 kW system is usually the sensible ceiling.

In the newer estates — Wollert, Donnybrook, Aintree, Cobblebank, parts of Tarneit — three-phase is increasingly standard, and 10 kW or larger becomes viable without a difficult approval.

This is a real advantage of building in a growth corridor, and one most people do not realise they have.

What it means for batteries

Less than you might think. Battery sizing is driven by your overnight consumption and your array’s surplus, not by supply type.

Where it matters is backup. Three-phase backup is more complex and more expensive, because maintaining all three phases during an outage is a harder problem. Many three-phase homes end up with single-phase backup on an essentials circuit, which is usually the sensible compromise.

What it means for EV charging

Single-phase charging delivers around 7 kW, which adds roughly 40 km of range an hour — comfortably enough overnight for almost any commute.

Three-phase charging can reach 22 kW, but it requires three-phase supply and a car that can accept it, and many cannot. For most households the extra cost is not recovered in convenience.

Should you upgrade to three-phase?

Rarely worth it purely for solar. The upgrade involves your distributor, possibly a new service cable, and a switchboard rebuild — frequently several thousand dollars. You would generally get a better return putting that money toward a battery.

It can make sense if you are already rebuilding the switchboard, if you have a genuine three-phase load like a workshop, or if you are building new and it is available cheaply at construction.

If you are building now and three-phase is offered at modest cost, take it. It is far cheaper during construction than as a retrofit, and it leaves every future option open.