Should You Get A 3 Phase Solar Inverter?

three phase solar inverter

There are a few things you need to know if you are getting a 3-phase solar inverter and expect to add a battery later.

I love three-phase solar inverters.

If your home has a three-phase supply and you do not want or need micro-inverters then my recommendation is to use a three-phase solar inverter over a single-phase model.

What the hell is a three-phase solar inverter?

A three-phase solar inverter  takes DC electricity from solar panels, chops it up and sends it out as AC electricity shared across a three-phase supply.

DC to 3-phase

DC in. Three-phase AC out.

They cost about $300 more than the equivalent single-phase solar inverter, but look the same:

three-phase solar inverter models

If it is a 3-phase Fronius it will say ‘Symo’ on it. If it is a 3-phase SMA it will be blue.

 

What the hell is a three-phase supply?

Most homes in Australia have a single-phase electricity supply. This means that they have one live wire coming in from the grid.

single-phase electricity supply

A single-phase supply

 

A three-phase home has 3 live wires coming in from the grid.

three-phase electricity supply

A three-phase supply

This means three-phase homes can pull more power from the grid.  Handy for particularly big loads such as a:

  • large air conditioner
  • pool heater
  • spa
  • sauna
  • electric car charger
  • etc.

And of course a three-phase supply means you can send much more solar energy back into the grid compared to single-phase (three to six times as much depending on your local DNSP rules).

How do you know if you have a three-phase supply?

Carefully (don’t touch anything!) 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 homes will have 3 like this:

three-phase switchboard

The main switch on a three-phase switchboard.

 

three-phase meter isolator

The meter isolator on a three-phase switchboard.

What are your options if you have a three-phase supply and want solar power?

If you have three-phase supply you can have either:

  • A single-phase solar inverter
  • Microinverters
  • A three-phase solar inverter

Any of these choices are valid. It will not affect how you are billed for exports or how much solar energy is self consumed.

But, I still recommend a three-phase solar inverter.

Why do you recommend a three-phase inverter?

Spreading the inverter capacity across the three wires coming into your home means that you don’t have to push the solar energy as hard to get it out to the grid. You’ll be increasing the local grid voltage less than a single-phase install and you’ll have less throttling or tripping off due to over-voltage issues. That means more solar power production with our high-voltage plagued Australian grid.

Voltage rise related solar issues are one of the biggest problems we see with installed solar power systems. I go in to detail on the causes and solutions for voltage rise issues here.

So to reiterate for the blog post skimmers:

If you have a three-phase supply I recommend getting a three-phase solar inverter. Why? Because it drastically reduces the chance of having voltage rise issues.

But not everyone agrees with me on this.

There is one downside to using a three-phase inverter other than the extra cost (expect to pay $300 to $500 more compared to a single-phase inverter). Three-phase solar inverters do make it much more expensive to have ‘Apocalypse Proof Battery Backup™’.

What is Apocalypse Proof Battery Backup?

My definition of regular battery backup is this: when the grid goes down your battery system powers some specially selected ‘essential circuits’. If the battery gets drained during the blackout, your home will black out too. In this configuration, the solar panels cannot charge your battery without the grid.

My definition of Apocalypse Proof Battery Backup : when the grid goes down your battery system powers some specially selected ‘essential circuits’. But if the sun is shining the solar panels help power your home and recharge the battery too. If you are careful with your consumption, you can carry on indefinitely charging the batteries with the sun by day and using the battery at night.

Why a 3-phase solar inverter makes Apocalypse Proof Backup very expensive.

If you have a three-phase home with a single-phase solar inverter (or microinverters) then, with the right battery – such as a Powerwall 2 – Apocalypse Proof Backup is easy and can be done out of the box:

single-phase solar inverter and AC coupled battery

A single-phase solar inverter and an AC coupled battery. The backup is all on the ‘black’ phase.

When the grid goes down in this configuration the battery system isolates the house from the grid (islands) and keeps 230V on the ‘black’ phase so the solar inverter does not shut down. The solar panels continue to send power to the house and battery. The solar inverter is throttled using frequency shifting if there is ever more solar power than the house and battery can handle.

But if you add a battery to a system with a three-phase solar inverter it is more complicated. If the grid goes down you need to keep 230V on all three-phases to stop the solar inverter shutting down. A battery with a single-phase battery inverter (such as a Powerwall 2) cannot do this. You will be able to have ‘regular’ backup – but once the batteries are drained you’ll have no power until the grid comes back.

The solution to this is expensive. You either need a three-phase battery inverter – and if you know of one please let me know in the comments – I’ve never seen one for sale. It would look like this:

three-phase solar and battery inverter

three-phase battery inverter and three-phase solar inverter

Or you have 3 batteries and battery inverters – one on each phase. But again – I don’t know of any battery systems that can play nice with a separate three-phase solar inverter. The Powerwall 2 cannot work in this configuration. Yet.

Or of course you could swap your three-phase solar inverter out for a three-phase hybrid inverter and DC Couple your battery:

 three-phase hybrid inverter

A three-phase hybrid inverter.

But all these options are very expensive. So if you are choosing between a three-phase solar inverter and a single-phase solar inverter/microinverters the question you have to ask your self is:

What’s more important to you? Apocalypse Proof Backup™ or stable solar generation?

In my humble opinion it is better to have a system that operates well 99.9% of the time (when the grid is available) over one that operates really well 0.1% of the time (when the grid is down).

But perhaps your grid electricity goes down much more than that and getting through long outages is your priority. In that case you may want to install a single-phase solar inverter on your 3-phase supply.  Just make sure that your installer checks your local grid voltage and voltage rise before you get solar installed. And hope that your local grid voltage stays low in the future.

You could also install a three-phase hybrid inverter instead of a three-phase solar inverter. But bear in mind that any future battery must be compatible with that inverter – often that is only 2 or 3 battery models and they may be obsolete by the time you decide to buy them.

So choose wisely three-phase dweller. And do the right thing based on your local grid voltage, your local grid reliability and above-all your zombie tolerance.

About Finn Peacock

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

Comments

  1. Tim Efthymiou says:

    Good write up Finn. 100%, not doubt, you should get a three phase inverter (if you have three phase at your home or business). This way you could split your solar system in three and split the load on your phases evenly. For eg. don’t have your air cond., fridge, dryer on the same load, split them around with your lights and power to even out the demand as not to overload one phase. Cheers for now.

  2. Finn wrote>> The solar panels cannot charge your panels without the grid.

    That should be … charge your battery…

    Mine can, being off-grid 🙂

  3. Brian Davis says:

    Hi Finn,
    Is it worth getting 3 phase power to take advantage of the bigger export limits,and the stability advantages you write about? I have also noticed that quite a few ground or air sourced heat pumps for heating and hot water are somewhat more efficient with 3 phase, or only come in 3 phase, so combined, I am wondering whether it is worth the installation costs?
    Cheers.

    • It depends how much they are going to hit you up. Getting 3 phase on a new build is not much more than single phase. Adding 3 phase to an existing build can be very expensive – depending on your site. Your DNSP can quote you yo upgrade.

      Having 3 phase is going to become more important as the voltage on the grid gets higher (as more solar goes in) and as people need to charge their electric cars. And yes – heat pumps are a but more efficient with 3 phase.

      • Ian Thompson says:

        Hi Finn

        A possible disavantage of using 3-phase inverters.

        I have 6.24 kW of panels arranged in 2 MPPT strings on an SMA 3-phase 5 kW inverter, installed nearly 2 years ago This worked very well at first, but as more and more houses installed PV, I noticed our power production was dropping very noticeably. On further investigation (using the Smart Meter, and the inverter’s read-out), I found the 3 phases were reasonably balanced in the morning and evenings (little PV generation), but during the morning 1 of the phases would go very high – approaching our 254 Vac regulated limit (240 V +or-6%). In the afternoon, another of the phases would approach that limit, but the 3rd phase would always stay at about 242 V.
        My inverter’s manual says that it commences throttling (or perhaps better described as limiting) at 250 Vac, and limits to zero output at 255 V line voltage. I was noticing our inverter was limiting ALL phases, if ANY phase was high. The current on each phase was the same.
        Seems like an opportunity lost – it would have been good for the inverter to redirect power on a high phase, to a lower phase – although I guess there maybe grid stability if all inverters had this feature. I can see it would make sense to the manufacturer, to design each of the phase inverter outputs to be rated at 1.67 kW (x 3 = 5 kW).
        But, if I had a single phase inverter, I could have simply swapped it to the consistently low phase, and all would have been good. Clearly, the PV generation on the grid was not being managed very well – and many 3-phase consumers were fitting single phase inverters to save cost (or – the installers were promoting this, to offer a better “package”).
        The Utility stated they were powerless to do anything – but appear now to have found a way, after I escalated this up to our Energy Minister.
        So – after experiencing equipment damage (CFL lights, motors, power supplies) from the excessive voltages (but within the regulations), and a loss of significant feed-in tariff, we are now back to where we should have always been.
        In this respect (Utility has little control over grid management), I suspect there is a weakness in the REBS scheme – management of the grid has been usurped by the installation companies.

  4. Mark Shueard says:

    Hey Finn
    You didn’t touch on the other ( and BEST ) alternative, perhaps because it’s unusual for most people to have the roof space.

    I have
    3X solar arrays + 3X single phase inverters + 1X Powerwall 2 = bill bliss and I have Apocalypse Proof Battery Backup™ too.

    Not everyone has roof space for 3 separate arrays ( I have 57 panels ) but if there is the possibility of such a system it has one other benefit over a three phase inverter. REDUNDANCY

    • That’s absolutely a valid design and a cracking system. But it is much more expensive. In terms of hardware, 3 x 5kW single-phase inverters will cost about 50% more than one 15kW three-phase inverter. The inverter installation is 3x the work. And you don’t get the voltage and frequency stability benefits of a three-phase inverter.

      You do get the redundancy though – as you say.

      • Mark Shueard says:

        I got lucky with the economics of all stages and I did not do it all at once.
        It’s worthwhile looking into if you have the roof space,.

    • Greg J Greet says:

      I have a similar set up (3×10 panels) & 3 inverters which @ THAT TIME were not that much dearer. The other advantage of the setup was the internal resistance of the inverters was lower than a single inverter allowing lower threshold for energy capture &c.p. higher energy yeild.

    • WTF is apocalypse proof backup?

      • Mark Shueard says:

        I was quoting Finn.
        It’s a funny way of saying you can have a blackout go indefinitely and still have power because the battery is charged by the PV system even though the grid is down.

  5. Thanks Finn. I understand that Enphase is just in the process of releasing a 3 phase solution also, which potentially provides an addition option for consderation. This might also be critical for anyone who has shading issues.

    • Yes – the 3 phase component for Enphase should arrive is Australia any time soon. If you have shading you can also use Tigo optimisers on a string system. It is very cost-effective to selectively add Tigo to only the panels that get the shade.

      • “the 3 phase component for Enphase should arrive is Australia any time soon”

        I thought Enphase 3-phase components are available in market now. I am getting an installation done in next couple of days with IQ7+ Enphase mico-inverters with 3-phase cables and components.

        I hope the installers are not planning to use single phase components.

        @Finn is it possible for you to confirm the availability?

  6. Onya Gordon…. and I’ll bet you also don’t have harness your horse to Ferrari in case the price of fuel goes up.

  7. If I were in the market for a 3 phase solar or battery system, one of the things I would want to understand better is how they deal with unbalanced loads across the phases. Bear in mind that most of the loads in a domestic environment are single-phase. Only certain loads, like large air conditioners will be 3-phase. In a domestic environment I would say you are generally guaranteed to have the loads across the phases unbalanced. I would thus want to be certain that my solar and battery system can cope with that, and how efficiently they cope with that.

  8. I’m not an engineer but could you have a dummy load on each phase that automatically switches on when supply exceeds demand?

  9. I live in an area with very low grid reliability and 3 phase. So battery system with Apocalypse Proof Battery Backup is important to me. Because of that I thought it worth pointing out a couple of additional gotchas:-

    1. I suspect 3 phase solar inverters are always likely to be a problem if you think that 3 single phase batteries are the solution to allow the solar to work in a blackout with the battery for ANY solution that uses frequency shifting to throttle solar output. The problem is that in this setup, you would need to use frequency shifting on individual phases to make sure you can reduce solar output when needed and the battery and household loads can’t absorb all of the power. The problem with this is that when you do this, the 3 phases will enevidably move independantly and at some stage they will not be 120 degrees out of phase as would be required for true 3 phase loads. While a lot of use cases will not care about this if there is no 3 phase loads, I doubt any knowledgeable vendor or installer would want to install like this for fear that this might 1 day break a 3 phase load of an unsuspecting end user. Solution to this would be to use some other mechanism than frequency shift of throttling of solar output (and this would probably bring other benefits), but that does not seem to be the way the industry is moving at the moment, Of course the other option is 3 phase solar and battery inverters that can supply different loads to different phases in a blackout, and also charge the batteries from whichever phases have the spare solar power, but again I am not aware of any products that are doing this, and all the standards solar 3 phase solar inverters must follow is more about ensure equal output on all 3 phases for grid stability, which is totally unsuitable for islanded requirements in a blackout.

    2. For anyone thinking that the solution to get “Apocalypse Proof Battery Backup” setup is to use micro inverters on 3 phases, or even 3 single phase inverters to get the benefits of solar on 3 phases AND battery on single phase to give the backup. The problem is that AS4777.2015 has requirements that even single phase inverters must trip off if there is a phase unbalance. So technically Mark Shueard system if build today to AS4777.2015 requirements probably should have solar tripping off in a blackout. I am guessing that the reason it probaby works for him is that the solar is either pre AS4777.2015, or implemented in a way to get around this. But I thought this is worth pointing out, because it would be unwise for people doing this type of install to just assume it works. Same thing applies for micros, and new enphase micros in particular. I like many people have enphase micros install across 3 different phases. With my old M215 and old Envoy (pre AS4777.2015) each phase worked in isolation (solar could keep working on any phase that is up, irrespective of what the other phases are doing). But with newer S270 and new Envoy-S AS4777.2015 compliant setup, when one phase goes down, the whole system goes down. This is a massive “incompatibility” with the current AS4777.2015 standards that all grid connected inverters must comply and any requirement for the “Apocalypse Proof Battery Backup” that I really feel needs to be addressed in the standard.

    Finally Finn, I am curious about your comment to Marks post above that his setup “And you don’t get the voltage and frequency stability benefits of a three-phase inverter.”. Can you expand on what you are talking about there. When I 1st read, I assumed you might have been suggesting his setup did not address the voltage rise issue, but I would assume a 15kw 3 phase inverter would trigger exactly the same rise as 3 single phase inverters pumping out 5kw?? Or are 3 phase inverters somehow outputting between the phases, rather than between active to neutral. I have not got my head complete around it, but I guess if you are putting output between phases at 400v rather than between active and neutral at 230v that will be less current for the same output, which is less voltage rise??

    • Mark Shueard says:

      While I have 3 x identical ( BOSCH ) inverters, 2 of them are pre AS4777.2015 profiles. The one that is running on the main load and battery phase is one of these.
      I too struggle to understand voltage shutoff /throttle / ramp up / requirements of the latest standard. One of these inverters meets that spec but has never shut off or ramped due to voltage. The other two have never shut off either, I have seen the main phase voltage at 256 V regularly and touching 258 at times, never shuts off.
      I too didn’t understand what Finn meant regarding voltage stability benefits, all I can say is I have never had any inverter go offline for voltage spiking.

      • All this is a complicated area that not many people understand well including a lot of installers (or for that matter myself so always good to find people who know the details and can reliably educate us all). The fact that you are using pre AS4777.2015 on your battery phase probably has the advantage that there is probably no chance a phase imbalance was you would experience in a blackout result in your solar not being able to work in a blackout. But there is the downside that this inverter and profile probably does not support frequency ramping (where solar output can be progressively throttle to balance generation and load). This does not mean you can’t use the solar in a blackout, but will probably just resulting in more “banging” the solar inverter on and off, something that some people have had some concerns might impact the longevity of the inverter.

        BUT, having said what I have said above, irrespective of what it says in AS4777.2015 about the requirement for even single phase inverters to shutdown on phase imbalance, I would not be surprised if that is often not implemented in single phase installs, and especially if they are not all done at the 1 time. I suspect this would be very easy for the install not to do. As near as I can figure out, to do this, you would need to install a bunch of extra stuff to even know that there was a phase imbalance which would not normally be provided with a single phase inverter install. So apart from complying with an overly draconian standard, there is probably very little reason someone on the cold face would want to go to the effort. You will probably find that the main target was micro’s which are more commonly spread across 3 phases in 3 phase setups. And so my guess those responsible for the standards where probably more interested in checking that people like Enphase had this implemented, and in truth with the centralised management that comes with systems like Enphase, it is probably more easy to implement. Doing so with single phase inverters is really a can of worms that would easily be circumvented by installers or home owners anyway.

        Voltage issue is way more complicated in the standards that a simple “below X volts is ok, and above X volts is ok”. This is probably made confusing by the fact that the profile information you see, often does not tell you all the detail. From my limited understanding (that might not be 100% correct), is there are a few things that pretty rigid (like voltage most be below 253v for inverter to startup etc). But beyond that it is more complicated. Some examples :-
        1. a lot of the voltage thresholds are based on 10 minute averages. So just because you see a temporarily higher voltage, does not mean it has to act on it.
        2. there are things like “volt watt mode” which will commonly not see the inverter switch off until voltage is 265V and this can be increased. See https://www.gses.com.au/wp-content/uploads/2016/09/GC_AU8-2_4777-2016-updates.pdf. So it is possible that your AS4777.2015 inverter was throttling, but not shutting off??? In fact it might even be tweaked so that even at 258v the throttling might be minor enough for you not to notice even if you were looking.

        But if I were you, and you voltages of 256v and 258v were not purely due to voltage rise (which will be there whenever your solar is exporting), I would be getting your supplier to tap the voltages to you down to be within the standard below 253v.

        • Mark Shueard says:

          Only the battery phase reaches 258V , the other two do not, they reach 252V.
          It is of note also that when my battery was re-installed in July ( swapped out a Sunverge for Powerwall) the installer swapped the phases around so he had red instead of white as the main phase. ( maybe he likes red better than white ). At the time, I though that is weird but if you have a colour fetish no problem , go for it. Then after he left I remembered that the white phase had the lowest voltage and that now my battery phase went from the lowest to the highest of the three phases in voltage. I’ve been watching it and being ready to ask them to come back if I got PV shutdowns – but so far I have not seen it. I do not believe there has been any throttling either on any inverter.

          I tested blackout and it performs as intended, phase 1 PV still functions ( only when battery is over approximately 80% full by design apparently ) and charges the battery.

    • Mark Shueard says:

      “”Or are 3 phase inverters somehow outputting between the phases,””

      Yes, each of my systems is on a separate phase, by compliance and SAPN approval requirement.

      • That comment was really a question to Finn about 3 phase inverters (you have 3 x single phase inverters). Single phase inverters output between Active a Neutral, with I assume each of your single phase inverters connected to a different active phase (Neutral is common). I assume 3 phase inverter is effectively the same, with 3 active phases and 1 Neutral. But this might be a bad assumption on my behalf and it could be that is outputs Phase A to Phase B, Phase B to Phase C and phase A to phase C. When you go phase to phase the voltage is 400 odd volts (not 230v), and this might have benefit for voltage rise (but I don’t really have my head properly so thus why I thought I would ask Finn, who might be across this better).

  10. Ian Thompson says:

    From experience, I feel you’ve got it wrong. I had an SMA 3-phase inverter fitted, and it throttles if ANY ONE of the phases goes high. We had 1 phase go high before noon, another at, and after noon – so a lot of throttling. Like many (most?) people, I rely on the feed-in tariff to make PV economic, as we use most power morning and evening, when PV is not producing. One of our phases was remaining significantly lower – so if I had a single phase inverter, I could have had it moved onto the lower voltage phase.

    • Have you checked your consumer mains and if it is not your fault (less likely to be you if you have a 3p inverter) asked for the DNSP to tap your local transformers down?

      • Ian Thompson says:

        Asked all that – my meter was logged, not my problem – suggested local transformer tapping change, but Utility (via Energy Minister) said that couldn’t be done, and nothing could be done as they would go outside regulations through low voltage in summer at the end of the line – I went back (through the Energy Minister) to say I was disappointed, as their own logging showed 1 phase low, so if they shifted generation from other phases, to this phase (called “NETWORK MANAGEMENT”), then everyone would benefit – the Utility said they couldn’t do this, as the consumers decide where their PV generation goes, and changes may upset their (3-phase) equipment, and would have to be done by contract electricians at the individual consumers homes (at their cost). Talk about a wonderful management system! I did point out the Utility could ROTATE the phases going into a 3-phase home (with single-phase PV), to bring the generation onto the low phase.
        No, they couldn’t do anything, except perhaps tinker with the HV feed line transformer tapping. Time passed….
        Now months later, even with the increased generation the phases are much better balanced, and throttling problem seems solved (for the moment – infill housing and more PV penetration may re-create the problem).
        I’m thinking the Utility responses may have been CYA – and the Minister may have directed them to sort it out.

  11. koen weijand says:

    you forgot to mention 2 more advantages of 3 phase inverters.

    3 phase inverters have the average panel voltage near ground, while in 2 phase inverters the average panel voltage is around half the dc value and has a grid frequency component. this means that there could be ac GFI trip problems, for example during rain and thin film panels with higher capacitance to panel ground.

    the other advantage is reliability . there are less capacitors needed in a 3 phase system, due to eased ripple current requirements. that is why 25kW, 3ph inverters are manageable in size and cost.

  12. 3 phase battery inverters? I can’t find any directly but I can’t see any reason why you couldn’t use a 3 phase solar inverter with batteries that are set up with a high enough output voltage. It’s just another DC source and provided it’s in the right voltage range it should work. Right?

    • Square peg in a round whole.

      Solar inverters tend to be designed to just pump out maximum power all the time. Battery inverters tend to have a bunch of extra smarts to enable sensible control of how the battery is discharged. eg balance demand in the home and things like TOU etc. With Australia’s limited FiT for most people there would be no point in discharging the battery flat out and exporting excess power to the grid from the battery etc.

      Then there is the fact that battery inverters often include battery chargers etc, that solar inverters will not have etc.

      • Agreed and valid points. Still not seeing these mythical 3 phase battery inverters anywhere except as part of a 3 phase hybrid inverter.

  13. Ian Thompson says:

    Everyone is talking about batteries as some sort of Nirvana.
    They must all be very, very big users.
    My use is modest – any I find from a detailed look at our consumption profile, that we would only save less than one-third of the cost of the battery pack, over it’s projected lifespan – on top of that, it is big money up front, and I haven’t even figured in the lost opportunity cost of the extra inverter(s), battery chargers, and the installation cost. Financially, for me at least, an extremely backward step.
    Going off-grid saves the connection fee, but extra inverters, because the grid-tied inverter has regulated anti-islanding features and will not run unless the grid voltages are present. Not sure if on-grid, the inverters would operate from a high voltage (350Vdc?) battery – but would like to know.

    • @Ian Thompson

      That’s the thing about the Tesla Powerwall, it will keep the solar inverters up (while the sun is shining) and powers the house while the grid is out. If there is excess solar, it will top up the battery. The Tesla Energy Gateway manages the grid connection and will island the house off the grid whilst keeping the inverters running (both the solar and battery inverter). The battery becomes the grid reference for the solar inverters, so they think there is grid power. When it senses grid mains has returned, it will reconnect the house back to the grid so that you can continue to export your excess solar or import power depending on the loads and supply.

      The battery in the Powerwall is 50Vdc.

      • Ian Thompson says:

        Hi Graham
        You may have misunderstood my words – maybe instead of saying I’d only save 1/3 of the battery cost, I should have said I’d only recover 1/3rd of the cost. After 10 years, I’d be out of pocket to the tune of 2/3rd the initial battery cost, plus the cost of installation and anything else required.
        Just doesn’t make economic sense.
        P.s. our Utility supply is very reliable – although I accept this is likely to be degraded with increased proliferation of domestic PV, unless more inertia and expensive synthetic inertia is added to the grid (e.g. SA, which has nearly twice the tariff that we have).

        • ” although I accept this is likely to be degraded with increased proliferation of domestic PV, unless more inertia and expensive synthetic inertia is added to the grid (e.g. SA, which has nearly twice the tariff that we have).”

          I would not believe everything you read, especially if it is coming from a COALition or Murdoch media.

          While there are many widely circulated anti renewable myths, these are not born out of the reality. eg :-
          1. that the only way to have stability in the network is to have a lot of traditional spinning inertia (coal and gas). That Luddite argument used to have a full stop to it, but now even those who wanted to make that argument have had to change that full stop to a comma and suggest that the synthetic inertia is expensive. But the facts don’t bear that out. The big SA battery has allowed for a reduction in spending on FCAS services to be reduced from $109m in 2016 and 2017 to a forecast of just $3.6m in 2018 (ie more than 96% reduction in the costs). See https://reneweconomy.com.au/tesla-big-battery-claims-its-first-major-fossil-fuel-victim-30614/. A large part of this will be the fact that keeping large amounts of traditional “inertia” in reserve for FCAS services is significantly more expensive than what it costs to provide it via what you call synthetic inertia, because “synthetic” inertia can respond much faster, and in a much more meaningful way. Sure some of this cost reduction would also be nothing to do with that, and more as a result of the batteries ability to break the energy companies pricing cartel for these services. But that too is just as relevant, and I would expect to bring the same benefits as we install more distributed solar and batteries so bring to again reducing the cartels pricing monopoly and improve the supply and demand balances which allows the cartels to game the market to their profit.

          Other references to this point :-
          https://reneweconomy.com.au/the-other-big-battery-that-has-quietly-changed-thinking-about-the-grid-15291/
          https://reneweconomy.com.au/aemc-sees-no-market-gaming-but-says-batteries-will-lower-prices-42472/
          https://reneweconomy.com.au/tesla-big-battery-defies-skeptics-sends-industry-bananas-over-performance-38273/
          https://reneweconomy.com.au/tesla-big-battery-is-already-bringing-australias-gas-cartel-to-heel-39541/

          2. SA power is expensive / unreliable because of large concentration of renewable power. Fact, SA power has always been expensive, long before the transition from coal to renewables. Fact the recent blackouts in SA were triggered by failures of coal and failures to bring gas online in failures and storms blowing down inter connectors. None of the expert reports are blaming renewable for the recent blackouts as near as I can tell.

          This reference covers most of it better than I ever could :-
          https://reneweconomy.com.au/five-myths-about-south-australias-renewable-energy-59004/

          3. We need coal and gas for reliable network. Not even the head of AEMO thinks that. ( https://reneweconomy.com.au/aemos-zibelman-transition-out-of-coal-does-not-mean-lights-going-out-32686/). Or the Finkel review or others actually dealing in this area.

          Unfortunately the COALition and Murdoch media continue to sow the seeds of FUD until it just becomes accepted and repeated fact by too many people unfortunately.

        • I should also add, I totally agree about your sentiments about the prospects of many people being in a position to make an economics return from batteries as it currently stands. I could not make the economics add up even before the significant Tesla PW2 price rises, and much less after it. So for most people, without special circumstances, or significant subsidies, if the only reason you are getting batteries is to save money, there is probably a LOT of places you will find a better ROI (eg solar). But I suspect this is because most people are only using to load shift power usage, and there is not enough arbitrage between FiT and peak rates to justify.

          So when used like this, we have to wait for electricity prices to rise, and/or solar FiT to fall, and/or batteries costs to fall, or longevity to significantly improve before this changes.

          HOWEVER, when the market develops, and we are able to sell battery services at a premium for things that batteries are actually good at, this could quickly change. eg if we sell some of our battery usage to provide FCAS services, or during peak wholesale prices, and or to soak up extra power at times of low demand to discharge and help the grid at times of high demand, we could potentially be paid enough to change the economics substantially. But it does not look like we are there yet, without significant subsidies, or using assumptions that are unlikely to pay out. When the government and regulators are committed to the RE transition, I am sure they will start working the regulation that will promote this, and the investment required, but until then we are stuck in a nightmare of our own making (ie high electricity pricing living in one of the most energy rich nations on earth).

          • Ian Thompson says:

            Hi Matthew

            I’d like to go one step further…

            To me, installing Solar PV, or adding a battery, should not necessarily be just about achieving ROI on the purchase cost – which as you say might have to await a significant subsidy, or for the price of power to increase.
            In my (non-self-centred) view, the economics of using a given technology should include recovering ALL of the associated costs – including the value of any subsidies (e.g. REBS), since after all, these are still costing us our tax dollar. Also, if the technology introduces undesirable features (e.g. the need for FCAS services, or an increase in the cost of power, or requiring an otherwise unnecessary increase in grid capacity), then these are costs that also need to be included.
            I agree that batteries are not “there” yet – except in certain special circimstances (TELSTRA have been using Solar and batteries for years in remote areas – very, very expensive, but cheaper than transporting diesel and servicing remote generators).
            I would dearly like to “load shift” our solar generation – today, we will produce around 37 units of power, but will use about 6-8 units overnight (lights, TV, cooking, refridgerator). Our tariff is about 26 cents/unit, FiT ~ 7c/unit, so every “shifted” unit will save 19 cents – not a lot, but it all adds up – just not enough to justify a battery system.

  14. William ANDREWS says:

    Hi Finn, 3 Phase sounds very complicated. If I had a single phase system with enphase micro’s, would I be able to install an apocalypse battery later? Bill WA

    • Ronald Brakels says:

      Hi William, Ronald here.

      Yes, that is possible. The Tesla Powerwall 2 is an example of an AC coupled single phase battery that can be added any time and can charge of solar panels during a blackout. (Unfortunately it is difficult to get and has just gone up in price.)

    • Actually, the devil is in the detail on this 1, as to if it will work with an apocalypse battery or not. If you have 3 phase, and you install Enphase today it is VERY likely that it will not work with a battery in an apocalypse!!

      I know this because I am in this position, and have so far battled unsuccessfully to get this working. Problem is there are parts of AS4777.2015 that mandates even single phase inverters must shutdown on phase imbalance. It is Enphases implementation (which technically they must as I understand it to be connected to the grid in Australia since Oct 2016) that causes the problem. It is hard to get detailed information on exactly how they implement this. But it is almost certainly the Envoy-S that implements this, and commands the micros to shutdown when it detects a phase imbalance. Now if you have 3 phases, even if you convince your installer to only install the micros on a single phase (probably only likely if it is a very small system, otherwise your distributor will want you installing the micros across multiple phases to keep balance), it is still likely they will sell and install the Envoy-S which measures and gives you consumption stats across the phases (you will probably want this as well as it is really handy to understand your usage). When they do that, it will be connected to all 3 phases to measure the consumption, and I would be pretty confident that it is this that enables them to detect a phase imbalance and then they must shutdown the solar.

      If this issue was easy to solve, I am confident it would have been solved. I initially had a deposit and install scheduled with 1 of Enphases largest installers in Australia, with the assurance this would work (despite making my concerns VERY clear and pointing them at the area in AS4777.2015 which would appear to cause the problem). But eventually they twigged to the issue, and after almost 6 months of working with Enphase for a solution, decided to return my deposit and did not want to play any more and said it could not be done. I have now gone to a new installer, who said if needed, they would work around it by installing 3 individual Envoy-S if they need to to make it work. I am now installed with a single Envoy-S, and sure enough, no support for Apocalypse battery (ie if 1 phase goes down, all phases go down). I was installed over 3 months ago, and still have payment outstanding because it was agreed this would be resolved before completion of the project. They tried to tell me “Enphase was aware of the issue, and had a profile they could install when the battery was installed” and suggested that was enough to get their last payment. But I smelled a rat on this 1, as they could not give me ANYTHING to support this claim, and so far refused to install that profile and test. Last communicate with them is they will get onto Enphase again, and try to arrange for this to be done, but that was over a month ago, and I still not have heard anything.

      There is a solution that does work. And that is to install a pre AS4777.2015 profile, and then it does work fine. But technically I suspect this is not supposed to be done, and does have 1 other downside. These profiles do not support frequency ramping (ie progressively being able to throttle output as frequency rises. The PW2 and other frequency ramping battery solutions use this to control the solar output, so that they have a better chances of keeping the solar on when the battery is close to full and being able to supply household loads from solar. Battery should work without this, as PW2 will just raise frequency till the solar trips off, but this will lead to more cycling of the battery and banging the solar inverter on and off, which long term might not be good for longevity of the solar inverter.

      I could believe solution might be to install multiple single phase Envoy-S and micros and have NO phase coupling between phases. Expensive and probably not as nice as single Envoy-S as I assume production and consumption usage will be 3 separate systems rather than presenting a consolidated view. But I am also suspicious that there might even be issues with this in certain circumstances where for example you have a neighbor with phase coupling or similar. There is lots of evidence in Enphase’s install documentation can happen. I did also wonder about all sort of ways to work around it in install. eg having Envoy and phase coupler on the grid side of the gateway which isolates battery and home in a blackout, and thus impacts ability of Envoy-S to send instruction to shutdown micros. But that testing shows that it is WAY more complicated than you would think, and despite doing this, somehow the micros were still detecting phase imbalance and shutting down.

      Story is different if you have an only Enphase system (per AS4777.2015 as I do). Despite being installed across multiple phases, it does not need the Envoy to work, and will all work without an issue on phase imbalance. But of cause you have the same limitation I have outlined above with lack of support for progressive frequency ramping of solar output.

      I think the issue is really with AS4777.2015. When it was written, it is clear to me that it was not written with any thought for batteries, and certainly not apocalyptic batteries. I suspect the standard really needs to be updated to better allow the inverter manufacturers to cater for this. More attention needs to be brought to this issue, because I am sure there are a lot of people buy micro solar on the assumption this will work, and it does not. Just like people surprised when their 3 phase solar inverters do not work with their shinny new battery in a blackout.

      Anyway, my council, if you are planning an Enphase micro install (or any micros for that matter as I think the issue is not Enphase but AS4777.2015), AND 3 phase, AND you want a battery that can keep the solar going in a blackout, proceed with extreme caution. oint out the issue to any potential installer, and get them to agree you will only pay once you have tested apocalypse battery support. To test that, you don’t need a battery. You just need to shutdown 1 phase, and confirm the micros on the other phases do not shutdown.

      • How big is your system?

      • Lawrence Coomber says:

        Matthew rework you battery storage from AC coupled to an independent and isolated solar PV DC coupled off grid solution working “in tandem with -but not connected with your existing system” and controlled by third party “remote smart monitoring and controls”.

        The loads circuits distribution between two or more power systems is managed and optimized dynamically by the monitoring and control system.

        Think more clearly about your energy solution objectives and imperitives from a clean slate perspective, and discuss this with you energy systems design engineer.

        Lawrence Coomber

  15. I read your post again, and might have misinterpreted your question in my previous long reply. If you only have single phase power at the property, as Ronald says, you should be fine if the installer installs solar and battery to support this. Single phase certainly simplifies thing as long as you are not limited by its limitations (ie more restrictive rules on how much solar and battery you can have).

    My concern in the previous post was to point out the potential problems if you actually have 3 phase power at the property, even if your Enphase and battery is only installed on a single phase.

  16. New Envoy-S / S270 micro system is 10kW. But I suspect it would not matter how big the system is if it is using Enphase micros and Envoy-S and monitoring 3 phases. Micros are on 2 phases. I can shutdown a phase with no micros on that phase and it will shutdown the micros on the other 2 phases.

  17. Hi Finn and all,
    This has been a very interesting discussion. One thing that has been alluded to, but I am not sure I have seen (or maybe understood),is whether it is “better” to to have a three phase system use micros (Enphase IQ7 & IQ7+?) spread across one or three phases, or use string inverter(s) with or without optimisers? I am at the point of deciding on a design, and the options can be a bit confusing 🙂

    The issues of apocalypse batteries is an interesting one, although with the payback value being negative on most of its functional life, that is maybe less appealing. Having some power during a blackout would be nice, but I have generally very stable power locally, so it usually doesn’t happen much or for long.

    • Ronald Brakels says:

      Hi Brian

      For an unshaded location the cheapest option is solar panels without microinverters or optimizers. For a shaded installation the decision is a little more difficult as it may be more cost effective to install more panels than use either microinverters or optimizers. It is possible to put optimizers only on panels that will be shaded and keep costs down that way. The economics of microinverters tends to work better for very small systems than larger ones. Where microinverters and optimisers excell is where a homeowner wants to get the most generation possible out of a limited amount of space. Especially if it is difficult to install panels at the same orientation.

      As for backup power, having a small generator can be more cost effective and (hopefully) reliable option. One reason is there may not be much energy left in the battery when a blackout occurs.

  18. Hi Ronald,

    We have a U shaped house, and the current 10KW designs we are looking at have panels on the East and North, with both aspects having two separate locations, depending on the system parts, and not all aligned vertically down the roof. There is capacity to have West facing panels as well if wanted. Shading isn’t really an issue – our own trees being the only likely shading, other than weird roof angles casting shadows during the morning or afternoon.

    Going three phase potentially lifts the 5KW export limit (for what that is worth, and presuming solar feed split across the phases), and prepares for things such as car chargers, heat pumps, etc, along with the improved voltage stability as per the benefits outlined by Finn.

    The cost of the system jumps about $2.5k going from mid range panels (Jinko 315W JKM315M-60) with a Fronius string inverter, to the same with Enphase IQ7 Micro Inverters, and then markedly ($6K more) stepping up to a tier 1 panel (LG NeON R 350W) with the Enphase IQ7+ Micro Inverters. Pretty much the same price between using the top panels with the micros or the same using a SolarEdge with P370 Power Optimizer Models.

    And the generator options does seem like a pragmatic approach 🙂

    • Lawrence Coomber says:

      Brian when the time comes to think more about those higher consumption “potential day time services load circuits” consider expanding the solar PV DC Bus and running an autonomous “daytime off grid circuits” solution for greater cost effectiveness independent of the grid, and particularly the advantage this strategy offers for DC Coupling for charging battery storage for dynamic controlled night usage.

      Lawrence Coomber

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