Three phase homes and batteries: one phase or all three?
By Daniel Carmont, licensed electrical contractor Lic# 92489
Nuvolt Electrical Solutions · 15 September 2026 · 13 min read
Energex's own EV charging guidance puts it plainly: most homes have single phase wiring. Some do not, and if yours is one of them, a battery quote has a question in it that a single phase house never faces. Does the battery go on one phase, or across all three?
I am a licensed electrical contractor (Lic# 92489), SAA accredited for grid connected solar and batteries, working from our workshop in Nambour. I install both designs. This post covers how to tell what supply you have, what each design can and cannot do, including in a blackout, the Energex rules that shape a three phase system, and how the federal battery discount treats the very large stacks that three phase homes tend to be offered.
One thing up front: this is not an argument that every three phase house needs a three phase battery. Sometimes one phase is the right answer, and I will say when.
First, find out what supply you actually have
Everything else in this post depends on the answer, so start here, and start safely. Look at your meter box and your main switch, but do not remove any covers or panels and do not touch anything inside. You are looking, not working.
The main switch is the best clue. On a single phase home the main switch is normally a single switch. On a three phase home it is normally three switches side by side, joined so they operate together. Two phase supplies exist too, and usually show as two joined switches. Treat this as a clue rather than proof, because older boards, subboards and unusual installations can mislead.
A photo settles it. Send a licensed electrician a clear photo of the meter box and switchboard with the covers closed. I can usually tell from that what supply you have and whether it suits the system being discussed, and confirm it at a design visit if one is needed.
If the answer is single phase, most of this post does not apply, and what size home battery you actually need is the better read. Converting a single phase supply to three phase is a separate job, quoted separately.
The two designs: one phase or all three
A three phase supply is three separate live conductors coming into the house, with the circuits in your switchboard spread across them. A few big appliances use all three at once: a three phase ducted air conditioner or pool pump, a workshop machine, or a three phase EV charger, which Energex says can be up to 22 kilowatts when it is connected and switched across all three phases. Everything else, the lights, the power points, the fridge, runs on one phase or another.
A single phase battery system connects to one of those three phases. It might be a single phase hybrid inverter with panels and a battery, or a single phase battery added beside an existing solar inverter. It is the same kind of equipment a single phase house would get, sitting on one leg of a three phase supply.
A three phase hybrid inverter connects to all three phases at once, with the panels and the battery both on its DC side. Charging, supplying the house and running backup, it does all of it across all three phases.
If you already have solar and are deciding whether to keep your existing inverter, that question is covered in hybrid inverter or AC coupled retrofit. On a three phase house the phase question sits on top of it.
What each design can charge from and supply
The physics here is simple, and it explains most of what follows.
A single phase battery
A single phase inverter can only put energy into, and take energy from, the phase it is connected to. When the battery discharges in the evening it supplies the loads on its own phase. The lights, power points and appliances on the other two phases keep drawing from the network, and a three phase appliance takes its supply from all three phases, so the battery can only ever help with one of them.
If the battery puts out more than the loads on its own phase are using, the extra goes out to the network on that phase. It cannot be steered across to the other two. Charging works the same way in reverse: energy comes in through its own phase only.
It is also a smaller system by rule. As the rules section below explains, Energex limits single phase battery inverters on a three phase connection to 5 kVA per phase.
A three phase hybrid
A three phase hybrid charges its battery straight from the panels on the DC side, and supplies the house through all three phases at once. Loads on every phase can be met from the battery, and a three phase appliance gets all three phases from the inverter rather than one. How the output is shared when the house is loaded unevenly has a name, unbalanced output, and it gets its own section below.
It can also be a much bigger machine. The four three phase systems we build use 25 and 29.9 kilowatt inverters. Three phase does not have to mean 30 kilowatts, though: Sungrow's datasheet for this family covers 15, 20 and 25 kilowatt models, and GoodWe's ESA three phase range runs from 5 to 30 kilowatts.
Backup: which circuits, and which phases, stay on
Backup is where the difference between the two designs matters most.
A single phase battery with backup has a single phase backup output. In a blackout it keeps alive the circuits wired to that output. Essential circuits, the fridge, the lights, the internet and a few power points, can be grouped onto it at the switchboard, which is the normal way to do it on a three phase board. What a single phase backup output cannot do is run anything that needs three phases. A three phase ducted air conditioner, a three phase pool pump or a three phase workshop machine stays off until the grid returns, however full the battery is.
A three phase hybrid has a three phase backup output. Sungrow's Australian datasheet for the SH25T, for example, lists its backup output as three phase, with a built in 63 amp bypass for whole home backup. That is what makes it possible to keep three phase loads running in a blackout at all.
Possible is not the same as guaranteed. Whether a ducted air conditioner actually runs in an outage comes down to the inverter's backup power rating, its short term peak for motor starts, and how long the battery can carry that load. A big compressor can drain a battery quickly, which is why whole home systems usually shed the largest loads when the battery runs low. I cover that tradeoff in whole home versus essential circuit backup, and moving circuits onto a backup output is often where switchboard work comes in.
The rule of thumb I use: if a three phase appliance is the reason you want backup, only a three phase design can do it. If what you want kept on is the fridge, the lights and the internet, a single phase backup output can do that job.
Unbalanced output, and why it matters in an uneven house
Real houses are never loaded evenly across their phases. The oven might be on one phase, the pool pump on another and the bedroom air conditioners on the third, and the mix changes minute to minute.
A three phase inverter's unbalanced output rating describes how differently it can load its three phases. An inverter that supports fully unbalanced output can supply each phase according to what is on it, rather than holding the three phases roughly equal.
It matters most in backup. With the grid gone there is nothing else to top up a busy phase. If an inverter can only deliver about a third of its rating on each phase, then in a blackout the busiest phase sets the limit, and a load can trip on that phase while the other two have capacity to spare.
This is datasheet territory, so read the line rather than the brochure. Sungrow's Australian datasheet for the SH25T lists support for 100 percent unbalanced output in backup and on grid mode, and Sigenergy's Australian datasheet for the SigenStor three phase controller lists unbalanced output as supported. For any three phase hybrid you are quoted, ask what its datasheet says about unbalanced output, and in backup mode specifically.
The Energex rules that shape a three phase system
These come from the connection standards Energex applies in south east Queensland. Ergon Energy Network publishes the same standards for its network.
Inverter capacity: 10 kVA per phase, 30 kVA in total
Energex's standard for small inverter systems, STNW1170, covers three phase connections of up to 10 kVA per phase and 30 kVA in total. It counts every inverter at the connection point together, existing and proposed, and a battery inverter's capacity is included in that total. That is why our biggest three phase systems use 29.9 kilowatt inverters, and why an existing solar inverter uses up part of the allowance before any battery inverter is added.
Above 30 kVA, a system is outside that standard and the application is a bigger exercise: Energex notes that applications for systems above 30 kVA need a design and a compliance report from a registered professional engineer.
Single phase inverters on a three phase connection: 5 kVA per phase
The same standard sets phase balance limits. On a multiple phase connection of 30 kVA or less, single phase solar inverters are limited to 5 kVA per phase and single phase battery inverters to 5 kVA per phase. Where single phase inverters are installed for both solar and a battery, they have to be on the same phase, and where single phase inverters are combined, the imbalance between phases cannot exceed 5 kVA. A balanced three phase inverter can go to the full 30 kVA.
In plain terms: a single phase battery on a three phase house tops out at a 5 kVA inverter on one phase.
Export limits: 5 kW per phase on a standard connection
On a standard fixed connection, a three phase system can export up to 5 kilowatts per phase at the connection point, and a battery inverter's export is counted as part of that limit. Under Energex's dynamic standard, STNW3510, a dynamic connection has a fixed default export limit of 1.5 kilowatts and can be allowed up to 10 kilowatts per phase when the network has capacity, with the limit sent to the system and the default applying whenever that communication is lost.
Export limits are why a big three phase system is designed around using and storing its own energy. On a 29.9 kilowatt inverter, a large share of what the panels make at midday cannot leave the property, and a large battery is where it goes instead.
The emergency backstop: 10 kVA and above
Queensland's emergency backstop mechanism applies to new, replacement and upgraded inverter systems where the aggregated capacity of all inverters at the premises is 10 kVA or above, which takes in every three phase hybrid in this post. Those systems need a generation signalling device fitted and the inverter configured for the demand response mode it uses, so the network can switch the system off for a short time in an energy emergency, at the direction of the Australian Energy Market Operator. It applies where the network's signalling service is available, which Energex says is all of its network apart from mainly some remote and fringe of grid areas. The Queensland Government says the mechanism has not been used to date.
Two details worth knowing. The capacity count includes every inverter on the premises, battery only inverters included, although an inverter supplied solely by a battery does not itself need the device. And a dynamic connection does not replace it: Energex treats the two as separate mechanisms, and a backstop signal takes priority over dynamic limits.
None of this is something you arrange yourself. It is part of the connection application your electrician lodges, and a three phase battery quote should mention it.
The federal battery discount on a big three phase stack
Three phase homes tend to be offered big batteries, and this is where the shape of the Cheaper Home Batteries Program matters most.
The discount is calculated on usable capacity, not the number on the box, and it is tiered. The first 14 kWh of usable capacity attracts the full certificate factor, from 14 to 28 kWh it drops to 60 percent, from 28 to 50 kWh it drops to 15 percent, and nothing above 50 kWh usable earns anything. The battery system also has to be between 5 and 100 kWh of nominal capacity to be eligible at all, so a system above 100 kWh nominal is not capped, it is ineligible.
The discount steps down on 1 January 2027. I explain how it lands on a quote in the federal battery rebate explained, and why past about 28 kWh you should be buying capacity for a reason rather than for value in what size home battery you actually need.
Where our four three phase systems sit against the 50 kWh line
All four reach into the 15 percent tier, so the top of every stack is lightly supported. Against the 50 kWh line itself:
[Fox ESS H3 Pro 29.9kW](/foxess-three-phase-solar-battery) with a seven module CQ7 stack is 48.72 kWh usable, just under the line.
[GoodWe ESA 29.9kW three phase](/goodwe-three-phase-solar-battery) with a full six module column is 49.9 kWh rated and 48 kWh usable, under the line.
[Sigenergy SigenStor 29.9kW three phase](/sigenergy-three-phase-solar-battery) with a full six module tower is 54.24 kWh, 52.56 kWh usable, which sits above the line. The capacity past 50 kWh usable is real storage that earns no discount, and a five module tower sits under it.
[Sungrow SH25T 25kW](/sungrow-three-phase-solar-battery) with a full eight module SBH400 tower is 40 kWh, comfortably under. The SH25T is the largest three phase hybrid Sungrow build for homes, which is why this system is 25 kilowatts rather than 29.9.
When a single phase battery is still the sensible design
Plenty of three phase houses are well served by a single phase battery, and I will quote one when it fits. The cases where it usually does:
Your backup needs are essential circuits. If what you want in a blackout is the fridge, the lights, the internet and a few power points, those circuits can be grouped on a single phase backup output. You do not need a three phase inverter to keep a fridge cold.
Your evenings are modest. A single phase battery inverter tops out at 5 kVA on a three phase connection, which covers a household whose evenings are lights, cooking and television far more comfortably than one running ducted air conditioning.
The three phase supply is there for one thing. Some homes have three phase because of a workshop, a bore pump or one large air conditioner, and the rest of the house is ordinary single phase load. If that one appliance does not need to run at night or in a blackout, the case for a three phase inverter is weaker.
You have good, young solar you want to keep. If your existing solar inverter is recent and well supported, a battery beside it may make more sense than replacing it with a three phase hybrid, within the capacity limits above. The tradeoffs are the same ones in the retrofit post.
Two cautions. First, a single phase design does not grow into a three phase one without changing the inverter, so if an EV, an electric kitchen or ducted air conditioning is coming, design for the house you are about to have. Second, the federal program supports one battery system per premises, and only the first time a battery system is installed, added to or replaced, so a small battery now and a replacement later is not a second go at the discount.
The honest version of the choice: a three phase hybrid when you want three phase loads backed up, a big battery, or the most solar your connection allows; a single phase battery when the goal is an evening top up and essential circuit backup.
Questions to ask on a three phase battery quote
Ask these and the answers will tell you more than the price does.
Is this a single phase or a three phase design, and why that one for my house? What is the total inverter capacity at my connection after the job, and does it fit the 30 kVA limit? What export limit applies, and has the emergency backstop requirement been included in the connection application? In a blackout, which circuits stay on, on which phases, and will my three phase appliances run? What does the inverter's datasheet say about unbalanced output in backup? And what is the usable capacity of the battery, and where does it sit against the 50 kWh line?
Reading a battery quote goes through the rest of the document line by line.
If you would like the right design worked out for your house, that is what the $299 solar and battery design visit is for: your supply, your switchboard, your metering and how you use power checked on site, and a written design you keep and a locked in fixed price within 3 business days, credited back in full off the installation if you go ahead within 30 days of the visit. If you would rather start at no cost, ask for a free estimate and upload clear photos of your meter box and switchboard through the secure link we send you. It comes back within 1 business day of receiving them, confirmed from your photos, or a $299 design visit if one is needed. We can't estimate without photos.
Common questions
Can I put a battery on a house with three phase power?
Yes, in two ways. A single phase battery system connects to one of the three phases, and a three phase hybrid inverter connects to all three. Under the Energex connection standard for small systems, a single phase battery inverter on a three phase connection is limited to 5 kVA per phase, while a balanced three phase inverter can go up to 30 kVA in total at the connection point, with every inverter on the property counted together.
Will a single phase battery back up my whole three phase house?
No. A single phase battery has a single phase backup output, so it keeps alive only the circuits wired to that output, and it cannot run three phase appliances such as a three phase ducted air conditioner or pool pump. It suits essential circuit backup: the fridge, lights, internet and a few power points. Backing up three phase loads needs a three phase hybrid with a three phase backup output, sized for those loads.
What is unbalanced output on a three phase hybrid inverter?
It describes how differently the inverter can load its three phases. Houses are never loaded evenly, and in a blackout there is no grid to top up a busy phase, so an inverter that can only deliver about a third of its rating on each phase is limited by the busiest one. Sungrow's Australian datasheet for the SH25T, for example, lists support for 100 percent unbalanced output in backup and on grid mode. Ask for the datasheet line for any model you are quoted.
How much can a three phase solar and battery system export in south east Queensland?
On a standard Energex connection, up to 5 kW per phase at the connection point, with battery exports counted in that limit. A dynamic connection has a fixed default export limit of 1.5 kW and can be allowed up to 10 kW per phase when the network has capacity. Connections under the small system standard are also limited to 10 kVA of inverter capacity per phase and 30 kVA in total.
Does a three phase battery system need a generation signalling device in Queensland?
Where the aggregated capacity of all inverters at the premises is 10 kVA or more, new, replacement and upgraded systems need a generation signalling device under Queensland's emergency backstop mechanism, in areas where the network's signalling service is available. Battery only inverters count toward the 10 kVA total but do not need the device themselves, and a dynamic connection does not replace it. Your electrician includes it in the connection application.
Does the federal battery discount cover all of a 50 kWh three phase battery?
Only up to 50 kWh of usable capacity, and at reducing rates. The Cheaper Home Batteries Program applies the full certificate factor to the first 14 kWh usable, 60 percent from 14 to 28 kWh, 15 percent from 28 to 50 kWh, and nothing above 50 kWh usable. The system must also be between 5 and 100 kWh nominal to be eligible at all. The discount steps down on 1 January 2027.
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