Don’t Add Batteries To A 3-Phase Home Before Reading This

3-phase homes and solar battery systems

If you buy the wrong battery system for your three-phase home your electricity bill will not go down nearly as much as you expect. And with the economic return of battery systems being pretty marginal in even the best case scenario, it is super important that your battery gives you the best returns possible.

The bad news is: The wrong (or misconfigured) battery system on a three-phase home will only reduce grid electricity use on the battery’s phase. It is therefore essential that you buy a battery system that is capable of offsetting your grid electricity consumption charges on all three-phases.

The good news is: Many battery systems can do this. You just need to check that the one you buy works optimally with your three-phase supply.

This post will help you buy a solar battery system that plays nice with your three-phase home.

Warning: The salesperson may look you in the eye and tell you that the battery system will work just fine on your three-phase supply. But you need to dig deeper. You need to make sure that the battery will work optimally on your three-phase supply. Here’s what you need to know.

What is 3-phase?

Three-phase is a type of grid connection. It describes how your home is physically connected to the grid. All grid connected homes in Australia are either:

  • single-phase
  • two-phase, or
  • three-phase

Single-phase: Most Australian homes have ‘single-phase’ electricity. This means that they have one live wire to their home carrying all their electricity. If you have single-phase, you can ignore this post and carry on with your day.

Two-phase: Two-phase supplies are rare, but some people have them. Two-phase means there are two live wires going into your home. If you have two-phase – you need to read this post as 2-phase battery systems have similar issues to 3-phase battery systems.

Three-phase: As people get bigger homes and more powerful appliances, such as large air conditioners and pool heaters, they may need more power than can flow down a single wire. For this reason, more and more homes are getting ‘three-phase’ connections. three-phase means that you get three live (or active) wires instead of one. It follows that you can have three times the power coming into your home. If you have three-phase power, the phases are red, white1 and blue. Your single-phase appliances run off one of those phases. Any large, three-phase appliances connect into all three-phases. As electric cars become common, more people will start to upgrade to three-phase so they can charge the car more quickly.

There are a gazillion configurations to choose from when installing batteries on three-phase

When I first sat down to write this, I thought I’d quickly draw up the possible configurations available. Then it dawned on me that there are about a gazillion. I present 16 different configurations here with their pros and cons.

Don’t worry about understanding every single configuration. But I hope the following list makes you appreciate that it is really important that your solar installer understands what you need in terms of self consumption and backup from your battery and configures your system to suit. I am getting more and more cries for help from people who have dropped tens of thousands on three-phase battery systems that are not giving them the savings or backup that they expected.

Tip: If you are buying a three-phase battery system, ask your installer/salesperson which configuration they’ve gone for, then make sure it has the features you expect.

Tesla tip: Even if you are simply getting a Tesla Powerwall 2 on your three-phase home, make sure that you are getting 3 consumption CTs and your backup circuits will all be on the Powerwall’s phase.

Definition: A ‘consumption CT’ is a little power meter (Current Transformer) that measures your grid imports and exports.

So here are 16 of the possible configurations for a three-phase solar power and battery set up2. If you are buying a system from scratch it could be any of these. If you are retrofitting a battery and want to keep your existing inverter, then you will have a much more limited choice.

Don’t fancy plowing through 16 schematics? I don’t blame you! Go straight to the summary here.

Configuration #1: three-phase hybrid inverter

three-phase hybrid inverter + battery system

A hybrid inverter is a single device that you directly connect both your battery and solar panels into.

A 3-phase hybrid inverter will convert the DC power output of both your solar panels and your battery to 3-phase AC power.

The three-phase hybrid inverter will monitor your solar electricity production and household consumption across all three-phases using little meters called Current Transformers (CTs), which are the green things on the diagram. It will use this information to know when and how much to discharge your battery so that you always use battery power instead of grid electricity imports wherever possible. It does this by instructing the battery to push out just enough power to offset the grid imports in real time.


  • A 3-phase hybrid inverter balances your phases (which helps grid stability)
  • It minimises voltage rises to the grid (because any load is shared over 3 wires).
  • By default, the battery reduces your consumption across all three-phases, optimising your savings.
  • A relatively simple, installation.
  • If the inverter has a backup feature and enough power, it can back up every phase in the house.


  • It is expensive. There are only two-three-phase hybrid inverters currently on sale in Australia. A 5kW Fronius Symo Hybrid retails at about $4,000 just for the inverter3, and a SolaX X3-HYBRID-5.0T costs just over $3,000.
  • Can’t be done for AC coupled systems like the Tesla Powerwall 2 or Enphase batteries. This is for DC coupled batteries only. And the batteries must be compatible with the specific inverter model.


Configuration #2: 1 single-phase hybrid inverter with 1 consumption CT

1 single-phase hybrid inverter with 1 consumption CT + battery system

A single-phase hybrid inverter will convert the DC power output of both your solar panels and your battery to single-phase AC power.

In this configuration, the single-phase hybrid inverter will monitor your solar power production and household electricity consumption across only the phase it is connected to. This means you will only get the benefits of solar energy consumption on that phase.

If the inverter features backup, then you can only back up the connected phase.


  • A relatively simple, installation.
  • Cheaper than a three-phase hybrid inverter.


  • A 1-phase hybrid inverter does not balance your phases, so you are often limited to 5kW of exports by your DNSP.
  • All the load is going down a single-phase, sometimes causing voltage rise issues when exporting. This can trip or limit your inverter operation.
  • The battery only reduces your consumption across one phase, reducing your electricity bill savings.
  • Can’t be done for AC coupled systems like the Tesla Powerwall 2 or Enphase batteries. This is for DC coupled batteries only. And the batteries must be compatible with the specific inverter model.


Configuration #3: 1 single-phase hybrid inverter with 3 x consumption CTs

1 single-phase hybrid inverter with 3 x consumption CTs and battery

Some single-phase hybrid inverters allow you to connect 3 CTs, one for each phase. They can then export enough on the connected phase to offset grid imports across all three-phases. When this battery power gets to the 3-phase meter, the meter subtracts the power being exported on the battery phase from the power being imported on the other 2 phases to give you zero net imports as far as your billing is concerned. Nice.

Single-phase hybrid inverters controlled by a Reposit controller can do this.


Configuration #4: 1 single-phase battery inverter with a 3-phase solar inverter and 1 consumption CT

1 single-phase battery inverter with a 3-phase solar inverter and 1 consumption CT

If you want to retrofit a battery to an existing three-phase solar power system, or keep your battery and solar systems on separate inverters, then you can use a battery inverter that ‘AC couples’ into your switchboard. That simply means that it converts the DC from the battery into 230V AC that is wired directly into your switchboard.

If the system only has one CT, then the battery can only offset your consumption on one phase.


  • It can be retrofitted to existing solar systems without touching the solar installation.
  • A single-phase battery inverter is cheaper than a 3-phase one.
  • Your battery system and solar power system are separate making maintenance, warranty claims and upgrading simpler.
  • A three-phase solar inverter allows you to fit more solar panels now or in the future (3 times more funnily enough)
  • A three-phase solar inverter pushes the grid voltage up less when you are exporting solar electricity, reducing the chance it tripping or derating due to grid voltage rises.


  • Your battery savings will only be on one phase.
  • You can only back up the phase your battery is connected to.
  • It is not possible to charge the battery from the solar panels during a grid-outage because the 3-phase solar inverter needs to see 230V on all phases to operate. The battery inverter can only produce 230V on one phase.
  • A three-phase solar inverter costs more than a single-phase one.

Configuration #5: 1 single-phase battery inverter with a 3-phase solar inverter and 3 x CTs

1 single-phase battery inverter with a 3-phase solar inverter and 3 x CTs


This is the same as configuration #4 but the battery inverter allows you to connect 3 CTs, one for each phase. This allows you to have the benefits of battery energy self consumption across all three-phases.

If you have a choice, always choose this over the previous configuration as it will reduce your bills more, assuming you have any appliances connected to the other 2 phases.


Configuration #6: 1 single-phase battery inverter with a single-phase solar inverter and 1 consumption CT

1 single-phase battery inverter with a single-phase solar inverter and 1 consumption CT

This is the same as configuration 4, but the solar uses a single-phase inverter.

Advantages over configuration #4:

  • If the battery inverter offers the feature, it is possible to charge the battery from the solar panels during a grid-outage. The Powerwall 2 does this with compatible units for example.

Disadvantages over configuration #4:

  • A single-phase solar inverter pushes the grid voltage up more than a 3-phase one when you are exporting solar energy, increasing the chance of voltage rise issues.

Configuration #7: 1 single-phase battery inverter with a single-phase solar inverter and 3 x consumption CTs

1 single-phase battery inverter with a single-phase solar inverter and 3 x consumption CTs

The same as the previous configuration (#6) except the battery inverter allows 3 CTs, so you can benefit from battery self consumption across all three-phases.

The Powerwall 2 offers this feature and is simply a battery plus battery inverter in one sleek box. It can be used with a single-phase solar inverter as shown, or a three-phase solar inverter. But with a three-phase solar inverter your battery can’t charge from your solar during grid outages.

Tesla Powerwall 2 battery configuration - simplified diagram


Configuration #8: Three-phase battery inverter with a three-phase solar inverter


1 single-phase battery inverter with a three-phase solar inverter

Here the battery inverter is a three-phase device, which means that it converts the DC input into 3 AC outputs.


  • A three-phase battery inverter pushes the grid voltage up less when you are exporting battery power, reducing the chance of the battery inverter tripping or derating due to grid voltage rises. This is only an advantage if you plan to export lots of battery power to take advantage of high feed-in-tariffs or grid support functions like Reposit.
  • Battery savings are across all phases.
  • Backup is across all phases.


  • A three-phase battery inverter is more expensive than a single-phase one.

Configuration #9: Three-phase battery inverter with a single-phase solar inverterThree-phase battery inverter with a single-phase solar inverter

This is simply the previous configuration with a single-phase solar inverter to show you can mix a 3 phase battery inverter and single phase unit if you need to.


Configuration #10: Three batteries, three battery inverters and an inverter with a three-phase solar inverter

Three batteries, three battery inverters and a inverter with a three-phase solar inverter

If money is no object, this is one way to get lots of solar+battery energy and power into your three-phase home.


  • Fault tolerant. If one battery inverter goes down, the other two will hum along just fine until it is repaired.
  • 3 x the power of a single battery inverter


  • Expensive
  • Each battery can only backup and offset the phase it is connected to.


Configuration #11: Three batteries, three battery inverters and an inverter with a single-phase solar inverter

Three batteries, three battery inverters and a inverter with a single-phase solar inverter

Same as previous configuration, but with single-phase solar inverter – just to show it is an option for those who want more battery power than solar power.


Configuration #12: Microinverters on  a single-phase with single-phase solar inverter and one consumption CT

Microinverters on  a single-phase with single-phase solar inverter and one consumption CT

One for my fellow micro-inverter lovers. Yes, it is easy to add batteries to microinverters. But if you only have one consumption CT, you’ll only get the benefits on one phase.[1. My first battery (Sunverge) was set up like this. The installer, AGL, has decided to replace it with a PowerWall 2, with 3 consumption CTs for free. I’m not gonna stop them. ]


Configuration #13: Microinverters on  a single-phase with single-phase solar inverter and three consumption CTs.

Microinverters on  a single-phase with single-phase solar inverter and three consumption CTs.

If you want a micro inverter system with batteries, make sure you get one that can accept 3 consumption CTs like this.

This is how the Powerwall 2 battery system on my house will soon be configured.


Configuration #14: Microinverters on  all phases with single-phase battery inverter and one consumption CT.

Microinverters on  all phases with single-phase battery inverter and one consumption CT.

If you have your microinverters across multiple phases, then that is not a problem. The one disadvantage is if your battery inverter can charge from solar during a grid outage, you’ll only be able to charge from the solar panels on the battery phase. And, again make sure you have 3 consumption CTs like this…


Configuration #15: Microinverters on all phases with single-phase battery inverter and three consumption CTs.

Microinverters on all phases with single-phase battery inverter and three consumption CTs.

You get the idea.


Configuration #16: Microinverters on  all phases with three-phase solar inverter and three consumption CTs.

Microinverters on  all phases with three-phase solar inverter and three consumption CTs.

Finally – if you have microinverters on all phases and it is important to you that you can charge from all the solar panels during a grid outage, then a three-phase battery inverter with backup function will allow you to do that.


If you have a three-phase supply and want to install batteries your options are vast.

My advice If you are starting from scratch:

  • If you  want to install as much solar PV and battery power as possible, then consider configuration 1.
  • If you are starting from scratch and are happy with 5kW of solar inverter power and 5kW of battery power, then a single-phase battery inverter, AC coupled with 3 consumption CTs is a good choice.
  • If being able to charge the batteries from the solar during a grid outage is important to you, then you need a single-phase solar inverter (configuration 7). Otherwise I always recommend a three-phase solar inverter (configuration 5), as they handle voltage rise issues better.

My advice If you are retrofitting batteries to an existing system:

  • When retrofitting, your choices are constrained by what you already have installed (unless you want to throw your existing solar inverter in the bin). For most people a single-phase battery inverter with 3 consumption CTs like configuration 5, or configuration 7 is a good choice.
  • If you are retrofitting a battery and want bags of battery power available to export because you believe it is your duty to support the grid, then a three-phase battery inverter is for you (e.g. configuration 9).

Or if it all looks a bit too much, simply engage an experienced solar+battery installer, who can decide  the best design for you. Just make sure you are clear in your requirements. Tell the installer:

  1. If you want self consumption on one or all phases
  2. If you want backup on one or all phases
  3. If you want to charge your batteries from your solar panels when the grid is down
  4. How many batteries and solar panels you want now or in the future

Then your installer will know which of the 16 configurations to work with, or might invent a whole new one just for you. You can engage 3 great installers for quotes on battery systems and retrofits here.







  1. shown as black on the diagrams
  2. I haven’t even included DC coupled systems with Solar Controllers or DC Converters
  3. And the Fronius Symo Hybrid is only compatible with a Fronius Battery at time of writing
About Finn Peacock

I'm a Chartered Electrical Engineer, Solar and Energy Efficiency nut, dad, and founder of My last "real job" was working for the CSIRO in their renewable energy division.


  1. Tony Jacques says:

    Good advice. However, you need to have a good installer. The guy who put in my system claimed vast experience and insisted my 3 phase system had to be deconstructed and re-configured to single phase to handle the selected inverter and battery. Only after installation when the owners handbook became available was I able to read that both units were configured to accept single or three phase. I feel seriously ripped off, but – buyer beware I guess.

    • Justin Smith says:

      You should thank him, not feel ripped off. If you can run your house on a single phase then you should. It is cheaper and more efficient.

      • Ah NO.
        This sparky wasted a heap of time reconfiguring the wiring when it didn’t need to be.
        Did he ensure the cable to the grid can handle the entire load?
        Or did he replace that to the pole/pit too?

        But generally, for any given electric motor of the same size, the 3-phase version will consume less power, start easier and be more reliable.
        Most certainly will not use less power on single phase.
        And for many installations, there is less copper required in 3 small wires versus 2 larger wires to supply the same load.

      • Lawrence Coomber says:

        Justin wrong.

  2. #17 – 1 battery, 3 Inverters.

  3. Lawrence Coomber says:

    Ron thanks for that, you have put a lot of effort into this very well prepared report.

    You have also brought into the frame another (unintended) consideration for some new potential solar PV customers at least; and that is going directly Off Grid at the beginning without traversing the inefficient and uneconomical route of On-Grid then to Off-Grid moving forward, which will soon become a commonplace consideration.

    I am referring to fully featured commercially focused Off Grid solutions though, for modern energy centric lifestyles, not the energy starved and problematic systems from past eras.

    Typically a modern domestic premises (starting point) Off Grid solution would be one of around 12 kW+ of Solar PV and 100 kWH+ of Battery Storage; DC Coupled to a 15 kW+ 3 Phase Standalone Inverter. A maximum efficiency well oriented design with minimal power conversions; operating at higher voltage therefore much less current, requiring much reduced lighter cabling and circuit protection. Importantly these designs are modular systems that are easily scalable up also.

    The PV component seems at first glance to be the sticking point for many domestic premises but this is not always the case. New Domestic Off Grid solutions PV mounting technologies are already available that offer alternative options to being totally beholden to inefficient oriented rooftop structures.

    Lawrence Coomber

  4. Ted Green says:

    Thanks for this – how can I tell whether my home is 1, 2, or 3 phase – it it stated in the fuse box or elsewhere?

    • Carefully look in your switchboard. Count the ‘poles’ on your main switch or meter isolator. If you have single phase you’ll only have one. Three-phase you’ll have 3.

      e.g. I have 3 phase:

      • Ted Green says:

        Thanks Finn, checked and I’m single phase. Similar labels to yours – “Normal supply main switch”, and there’s only one of them, and one for my PV too.

  5. Nice article Finn. How about a grid-connected 3-phase system using three Selectronics SP-Pro inverters, ac-coupled? Where would that fit in your list of configurations?

    • I’m not a SP Pro expert, but I think that would be Config #10a which I left out to see if you were paying attention 😉

      The SP Pros are the Battery Inverters.

      SP Pro and Fronius 3-Phase Integration

      • Thanks! It’s slightly better than that though, as it doesn’t require 3 separate batteries. One battery inverter is designated as the “master”, controlling the entire battery as single unit across all phases.

        • So the 3xSPPros are essentially connected together and act as one 3-phase battery inverter? Effective but very expensive way to do it. Especially with 3 x Fronius single-phase solar inverters too.

  6. Hmm, it is interesting? You always said “don’t put batteries! Wait! They don’t pay for themselves!”
    Now you already have a battery and even trying to update it..Thanks for the advice!

  7. Hi Ron – fabulously useful post. It’s so hard to find this kind of detailed info anywhere on the web. Thanks!

    A couple of questions:

    1. “Configuration #5 & #6”: I don’t see how this provides “the benefits of battery energy self consumption across all three-phases.”. It looks to me like only one phase gets the battery’s input. Or have I misunderstood something?

    2. I am building a house with 3 phase and we hope to put in a solar system with battery (maybe a small modular one for now, and a larger one later). We will have a heat pump running on 3 phases, otherwise everything else will be on one phase (unless there is reason to spread the load?). I want to know if there is any point spending extra for a 3 phase hybrid inverter and connecting both the panels and battery to all phases, or if it is just as good to leave the heat pump running on 3 phases (we’ll never want to run that from battery) and put everything else on a singe phase? I don’t know the cost difference between a genuine 3 phase set up and a single phase one (do you?) but I imagine it is quite a bit extra for little gain. Thoughts?

    BTW, I have read about the IMEON 3-phase hybrid inverter: (add this to your other two available in Aus!). It sounds smart, but no idea what the cost is compared with their 2-phase inverter. No idea of their reliability, etc. either.

    Keep up the great posts!


    • Bloody Ronald – always wallowing in my glory!


      1. It is explained in Configuration #3:

      “They can then export enough on the connected phase to offset grid imports across all three-phases. When this battery power gets to the 3-phase meter, the meter subtracts the power being exported on the battery phase from the power being imported on the other 2 phases to give you zero net imports as far as your billing is concerned.”

      2. I’d go for a single phase battery system with 3x consumption CTs, unless you have an enormous heat pump and want to run it off battery power.

  8. Ian l Gittus says:

    Sonnen and Imeon are other options.

  9. Dave Ritson says:

    OK, so what 3-phase battery inverter options are there available? (Or 3-phase hybrid all-in-one)

  10. Hi Finn,
    Is that red sign correct. Do you have only 1 solar panel connected?


  11. Rod Kemp says:

    Scotty’s question related to the first picture you put up which shows the “Warning dual supply” label and Voc is shown as 37.4V which surely can’t be more than one panel.

  12. Maria Gardiner says:

    Hi Finn

    Thanks for this. It is much appreciated. I am about the get a Tesla powerwall 2 installed on the AGL VPP (replacing the sunverge) and am on 3 phase. I don’t have much that runs on the 3rd phase – my aircon (which sucks the power like crazy so rarely use it at night – just run it during the day), the stove and a couple of outside powerpoints.

    I have found that i probably use around 50-70% of the battery just with usual overnight consumption. I wonder if it is worth it to have the third phase on the battery as well so that stove can draw from the battery? I guess it depends on how much they slug me to do this. Also in terms of having the 3rd phase on the backup, i only have a small bit of the 1st phase on the backup (just the fridge, the lights and a couple of powerpoints). Would there be any need to have the 3rd phase on the backup?

    Am i understanding this all correctly? Which option do you think i should push for when they install the powerwall? Assuming they will let me have any options at all!


    • The Tesla Powerwall 2 is a single phase battery system that can be used with 3 consumption CTs. That means it can be configured to give you the benefits of battery self-consumption across all 3 phases despite only being physically connected to one phase.

      Next time you talk to AGL, just say this:

      “Please can you confirm that I’ll get rewarded for self consumption across all 3 phases?”.

      • Maria Gardiner says:

        Thanks so much Finn. I just rang and asked and they confirmed yes! But I will be hovering when they do the changeover to make sure.

        I have another question that is not a three-phase question so not sure if it is okay to ask here. And if you have addressed it elsewhere I’m very happy to look there if you point me in the right direction. But have you discussed or thought about or calculated the optimal amount of power to leave in the battery to use for backup? It seems if you leave a higher percentage (20%?) then there’s all that wasted power just in case there is a blackout. But if you run the battery down to its permitted lowest point and there is a blackout you will be kicking yourself because the one time you needed this bleeping backup (that you paid $900 for!) it is not available.

        • Excellent question – and it is totally up to you. I just leave mine on the default setting and hope that any blackouts are not in the morning before 11am! But if your PW2 is set up to work with your panels when disconnected from the grid, then even if you are blacked out from sunrise, the solar will recharge the batteries as the sun rises.

  13. I realize you were no doubt trying to keep the schematics simple, but if we are talking about backup, don’t we need to also include some auto transfer/isolating switch/contactor arrangement. Please discuss.

    • Yes – you absolutely need a switch if backup is required and to also think about:

      Which circuits are backed up
      Backup circuits sub-board
      Battery bypass switch in case of battery fault
      If system can charge from panels during outage – and how? Comms or Frequency shifting
      Solar array size relative to battery inverter power for charging

      I think that is a whole other blog post!

  14. Thanks – I look forward to it 😉

  15. Jim Raleigh says:

    A very useful article but does not actually cover my specific (admittedly unusual) situation.
    I have a 28 panels (8.96kWp) connected in 2 strings (16 &12 facing in 2 directions) to 2 single phase (Solar Edge 6500) inverters each of which has one of the larger (RESU 10H) LG batteries attached and are connected to 2 separate phases of the 3 phase supply. Both inverters are configured to give me backup power on the relevant 2 phases.
    I am told that if one battery is charged and the other is not, it has been configured so that the second battery will be charged from the first string by feeding through the smart meter, and that consumption on the third (no solar) phase is taken care of by the smart meter using output from the solar connected phases.
    I have certainly seen a dramatic drop in my imported power and am exporting quite a lot, enough production to run my air conditioner through the recent summer and still get a negative bill.
    I do expect that it will not be so good in the winter as I have a large house and heating (in Canberra) can be a significant cost, but am waiting to see.
    Is my configuration as optimum as it could be or would I be better with changes.?
    PS: A side impact of my configuration that may interest you is that although I have a Reposit box installed, it is no longer connected. The reason is that to handle my situation I am told (by Reposit) that I would need to have it changed to a Reposit Infinite, but that if I did so, I would have to separate the two phases into 2 totally independent Solar systems rather than run the Inverters in a Master/Slave configuration as at present. This would prevent me monitoring the entire house as a single entity which I see as important.
    Secondly although it was originally connected, we discovered quite by accident that it was interfering with the Solar Edge monitoring, such that I had no visibility of consumption data, a fairly fundamental requirement. Once it was disconnected the Solar Edge monitoring worked just fine.

  16. mark wilson says:

    awesome article and great discussion too, thanks guys

  17. Thanks for the helpful article.

    I am in the process of building a 3-phase house including an off-grid Solar system. Solar panel capacity 12.2kW in two strings and planning 2 LG Chem Resu 9.8kWh batteries. Originally Fronius Symo 10kW inverter proposed, then 3 Fronius Primo 4kW; both with 3 Selectronic Battery Inverters 5kW 48V. Questions are now (suddenly, after almost 8 months) around the suitability of both the batteries and the inverters. I am now starting to query the advice I have been given.
    Has anyone got helpful ideas or experience with this type of system that I can use to assess the info I have?

    • Lawrence Coomber says:

      Hi Joan.
      If you are considering a 100% Stand Alone Solution Joan (not a hybrid solution) then the most cost efficient, reliable and enduring option for you to consider might be a DC coupled single 3 Ph inverter system.

      2 x LG Chem’s; 3 x Froniuos Primo’s and 3 x Selectronic Battery Inverters sounds about the opposite of simplicity; functionality and endurability. Can I ask Joan what has prompted you to now start to query the advice you have been given?

      Lawrence Coomber

  18. A helpful article. I have a question or two. I’m considering battery storage. My system was installed in Dec 2017. It’s a 3 phase Fronius inverter (not hybrid) was advised at the time not to spend extra money on this type of inverter as not needed for adding battery storage later. So what are my battery storage options I assume I have more than one.

    • Ronald Brakels says:

      Hi Pas, Ronald here.

      The easiest way to add battery storage to a home with an existing solar system is to AC couple it. This involves installing batteries with a battery inverter that provides DC power to charge them and changes DC power from the batteries into the AC power homes use. The most well known AC coupled system is the Tesla Powerwall 2. It has a built in battery inverter. But other batteries such as the LG Chem Resu can be AC coupled with a separate battery inverter. If you check out our battery comparison table:

      You will see there is a row which says “ÄC or DC Coupled?”. You can use this to see which are specifically made to be AC coupled. Where it says “N/A” it generally means it can be AC coupled using a separate battery inverter.

      As you have 3 phase power you are unlikely to have problems with inverter limits when you install an AC coupled battery system. (Unless your solar system is very large.)

      At the moment batteries won’t save you money, but so long as you are fine with that, good luck getting a battery system.

  19. Hi Finn,
    Reading Jim Raleigh’s post above interested me (no one has replied to him yet!). He is wrestling with large systems on a 3-phase supply – as I plan to too. My question relates to choosing between 3-phase and 1-phase inverters. I don’t know the relative costs of these inverters, but is there a “sweet spot” in terms of PV size and how to manage 3-phase or 1-phase inverters? E.g one could presumably install 2 small 1-phase inverters, or one larger (more expensive?) 3-phase inverter. I am contemplating 20 kW, so should I just be doubling up and using a separate inverter for each phase, or looking for a large 3-phase inverter? And presumably there is an optimum PV size that gives you most bang for the buck as far as available inverter sizes go.

    BTW, I will have most usage on only one phase, the 3 phases only being used for heating which I don’t expect to be able to manage from the solar anyway, even with 20 kW of PV!

    • In terms of solar inverter cost you’ll save about $1000 total with a good 15kW 3 phase inverter compared to 3 x 5kW single phase inverters (perfect for 20kW of panels).

      A great solution for big 3 phase solar and battery systems is the SP-Pro + Fronius (AKA Spronius).

      There are lots of factors to consider with 3 phase and batteries, as you can see, such as how you want your backup and self consumption to work, the resistance of your grid connection etc. So you really need a clued up installer with lots of battery experience to have a good look.

      • Thanks Finn. But I am confused by Spronius! Why do I need SP-Pro as well as Fronius. Aren’t they both inverters? I only plan to back up one phase, but want the solar to feed in on two phases. Does this make a difference?

        • The SP Pro is an AC coupled battery inverter. The Fronius is a solar inverter. The SP Pro talks to the Fronius inverter so the solar panels can be throttled when there is not grid available. This allows the solar to charge the panels without a grid.

          If you don’t have that comms link – the system will work fine, but if the grid is disconnected, once the batteries are flat they will not be able to recharge until the grid is reconnected.

          If you only want backup on 1 phase then…

          Advantages of 3 phase solar inverter:

          Cheaper hardware (about $1000)
          Cheaper installation
          Lower voltage rise to the grid (may or may not be an issue – depends on your local grid and how thick your grid connection wires are – you need a good installer to advise)

          Disdvantages of 3 phase solar inverter.

          Can’t use solar panels when grid goes down, because inverter needs to see the grid on all 3 phases to fire up.

          Advantages of 3 x single phase inverters

          Redundancy – if one fails you still have 2 phases
          You can run the solar panels on the backup phase without the grid.

          If ‘apocalypse proof’ backup is not an issue then I’d personally go for a 3 phase solar inverter and a single phase battery.

  20. Thanks Finn, very clear! So presumably a 3 phase *hybrid* inverter (e.g. Imeon, Solax) will do everything, including powering and charging from solar when grid is down? But it seems they don’t come with higher power levels.

  21. Hi Finn, thanks for the good article and advice! I have answered most of my questions by reading the article and previous questions and answers, but I would like to double check this last question.
    Our new system will be a 13Kw solar + PW2 on 3 phase power. I believe the inverter quoted is the Solaredge SE10K 3 phase inverter. CTs to each phase. Configuration #5 or #7 (but with a 3 phase inverter).

    From the 3 phases, I think we will request to use just 2 – one for the running everything in the house (with different circuits – PW2 connected to this phase) and the other phase dedicated to the Sanden HWS (with a timer to operate from about 11am to 3pm from the solar system). – The extra phase will have a CT installed just in case we need to use it in the future.

    In case of a blackout, the PW2 will be set to power a couple of circuits from the battery phase such as lights and dc ceiling fans and maybe one area of powerpoints.

    Is there any way that we can configure this system in a way that if we do have a blackout during daylight hours the system will be able to:

    Solar panels to continue charging the PW2?
    Solar panels to power the house if the PW2 is full or if the second phase requires power (HWS startup times)?

    Thanks for your help and great advice!

    • Ronald Brakels says:

      Hello Nico, Ronald here.

      The Powerwall 2 has full backup capability and, according to Tesla, during a blackout it can be charged by your solar panels. During the daytime during a blackout power produced by your solar panels will first go towards meeting household electricity consumption with any shortfall being make up by the Powerwall 2 storage and any surplus will be used to charge the Powerwall 2.

      Unfortunately, unless you have a Powerwall 2 lined up, it may be hard to get your hands on one. Tesla says they won’t be available until early 2019.

  22. Mhanks Finn

    That is a great help as I can now show my installer what I need. Little understanding of three phase by most of them! For Config 7 are there other battery inverters that are available apart from Tesla?


  23. Not sure if you are still reading these posts, Finn, but here goes just in case…

    I plan to have 3 phase power, with a 3 phase 16 kW hydronic heat pump plus the rest of the house on either just one or all 3 phases. We’ll have a battery set up to run as backup for grid outages (need to pump water, sewerage, etc.). But, if the power goes out, I don’t want the battery to power the heat pump as that will flatten the battery in about half an hour! Is there any way to prevent the heat pump from being powered by the battery?

    • Ronald Brakels says:

      Hi Jon, Ronald here.

      First off, I’ll mention that it can be much cheaper to use a generator to get through blackouts than batteries. So if cost is a consideration you may want to hold off for a while and see how much they fall in price.

      A 16 kilowatt heat pump is enormous and so I am thinking that might be its heat output and its electrical power draw would be 4 kilowatts or less. But that’s still enough to grain a battery.

      When you get your battery installed you can just have all your vital loads on one phase which your battery is connected to. Your 3 phase heat pump wouldn’t be able to run off that. But your installer might have a more elegant solution for you which will depend on what hardware you are getting.

  24. Andrew Hunt says:

    Is it possible / practical to have the current SolarEdge 3 Phase 5KW inverter easily connected to a battery. Asking for future proofing of a quoted system. I have heard mixed reports. Some saying it is easy. Others saying it is not feasible.

    Thanks in advance

  25. One other possible configuration I am planning to implement is as follows:

    My house has 3 ph and I’m on a high FiT and limited to my initial/legacy install inverter sizing, in my case 3Kw. I have 22 panels in 2 different orientations NE and NW on a dual MPPT inverter To maximise export and FiT revenue, I have removed all internal house loads off the solar phase L1 (my inverter is single phase). and put those load on the remaining two phases.

    I have a further 45 panels ready to connect up mounted on a rear shed. These will feed through a single phase 10kVA off-grid inverter and charge my EV which will also be a storage source for my house supply. The two phases servicing the house are disconnected from the grid and become common (joined) serviced by the single phase inverter which at 10kW has adequate short time overload capacity for all internal house loads. Fall back to the grid is automatic by a transfer switch. I plan to wire the panels in a 5x per string format which means the EV battery can also be charged directly from the panels in an emergency (ie if the inverter ever failed.

    • Lawrence Coomber says:

      Ian you have strong options from what you have on hand.

      A simple generation solution to consider – why not use your 45 panels to their full advantage and connect them to a 20 kW 3 Phase Stand Alone Inverter and “dedicated selected premises load circuits” to this Off Grid Strategy which is totally isolated from your existing On Grid System that is on a high FIT.

      This is a common strategy particularly for rural premises where pumping and irrigation circuits (or high current low duty cycle machinery) for example, are independently serviced by a second (and isolated) Stand Alone PV system.

      The extra bonus with this strategy is that you can easily connect a very efficient DC coupled battery stack to the Solar PV DC Bus and through “dynamic smart controls” exploit the battery stack to full advantage for the entire premises night time loads.

      Something worth discussing with your energy systems design engineer for sure.

      Lawrence Coomber

  26. Jason Dickinson says:

    I have installed a few AC retrofit inverters with battery storage on single phase houses with no issues.

    Now I have 3 phase costumers with existing PV systems (dc and enphase) that want batteries.

    Is the financial benefit that same if…..

    I use a single phase retrofit inverter and install 3 CTs, this will discharge into the connected phase and then subtract the excess into the other 2 phases.


    Do I wait for a 3 phase retrofit inverter to be released therefore discharging to each of the 3 phases evenly as required by the loads.

    Finn, be good to hear your point.

    I know goodwe are releasing a 3 phase retrofit this year.

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