Solar power and single-phase vs 3-phase power connections

Depending on where you live, your home may be fed by single-phase or 3-phase electrical connection. What relevance does this have for your solar PV installation?

 3-phase and single-phase power

Both single-phase and 3-phase electricity are used to transmit and distribute electricity. Depending on where you live and how much electricity you consume, your home will be fitted out with either a single-phase grid connection or a 3-phase grid connection. (Most homes have single-phase connections.)

Regardless of whether you have a single-phase or 3-phase connection, the appliances in your home all (almost certainly) run on a single phase. (3-phase power is used to power motors in certain industrial applications, but not in homes.) In the case that you have a single-phase connection, electricity flows in and out of your home through a single phase (imagine a single cable/circuit).

If you have a 3-phase connection, on the other hand, the electricity entering your home is divided into three separate phases (imagine three cables/circuits). Different devices in your home will be powered by these different phases. For example, your lights may run on one phase, while your washing machine and refrigerator may be on the other two phases.

The image below, from Prolux Electrical, illustrates how 3-phase power is ‘divided up’ for household & industrial loads. You can see that all three phases feed into the industrial motor, while the light globe and power point are each serviced by a single phase (represented by the yellow and red lines, respectively).

3-phase-power-prolux

Illustration of how 3-phase power works on types of electrical loads. (Image via Prolux Electrical.)

What the number of phases mean for your solar PV system?

If you don’t have a solar PV system, you may very well have no idea if you’re on a single-phase or 3-phase connection. Regardless of which one you have, the electricity you use is most likely being delivered seamlessly to all of your appliances – so it’s not really anything to be concerned about.

In the event that you want to install a solar PV system, however, phases matter. For a single-phase connection, a single-phase solar inverter should be installed – fairly straightforward.

For a 3-phase connection, on the other hand, there are a number of options. In most cases the best and simplest option is to get a 3-phase inverter, which will distribute the solar power evenly across all three phases.

Another option for a 3-phase connection is to install one single-phase inverter on one of the phases in the home (preferably the one that uses the most electricity/has the heaviest loads). The downsides of this approach are that 1) if the solar system is too large, the inverter could ‘trip out’ if the voltage for that phase goes to high, and 2) the solar energy may not flow to the phase where it is needed most. For this reason, with this approach it’s important to have your solar installer undertake an assessment to determine which phase is the best one – if you install on the wrong phase, the energy that your solar system generates could end up going to waste.

The third option is to install multiple (up to three) single-phase inverters, each one on its own phase. This could prove to be a more expensive option than simply using a 3-phase inverter, however, so it’s important to consult with several solar installers to collect a variety of quotes and opinions before making a decision.

Solar system size considerations

It’s also important to check whether your phase connection will have an impact on the size of solar system that you’re allowed to install. Generally speaking, tighter solar system size limits are placed on homes with single-phase connections than those with 3-phase connections.

In South Australia, for example, solar PV system size is limited to 10kW in buildings serviced by single-phase connections, whereas homes and businesses with a 3-phase connection may install systems as large as 30kW. Generally speaking, this is why a requirement for special approval from utilities for grid-connection of large solar PV systems in remote areas (which are sometimes serviced by ‘single wire earth return’ or SWER lines) is more common than in areas with high population densities.

AC vs DC electricity explainer (just in case)

AC (alternating current) electricity. AC electricity is what most household electrical appliances require to operate. The other type of electricity, DC (direct current), is what solar panels and batteries produce. DC electricity is converted to usable AC electricity through a device called an inverter. AC current is distinguished from DC current primarily by the fact that its direction ‘switches’ back and forth rapidly, whereas DC is uni-directional. Without getting into the technical details as to why, this property makes AC electricity more suitable for long-distance transmission.

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© 2016 Solar Choice Pty Ltd 

Top image via Wikipedia

Comments

  1. I have been quoted the same price to install a 5.4 kwh solar system on my house. One is through my electrical company with a 1 phase inverter system and the offer of a $.22 buy back program for 2 years.
    My other quote is for the same price and system with a 3 phase inverter system but I wouldn’t get the $.22 buy back program with my energy company. My house is set up as a 3 phase system (it has the potential to be split into two units which I may do in the future) so would it be best to go with the 3 phase inverter at this time?

    1. Hi Julia,

      In our experience, ‘extra generous’ feed-in tariffs these days usually have hidden costs elsewhere that tend to cancel out the benefits of the higher rates. Make sure you take a close look at the net benefit that the system is likely to deliver (you can use our solar payback calculator to work out some indicative figures).

      Give us a call on 1300 78 72 73 if you’d like to discuss your options in further detail, or if you’d like to have a look at other quotes from your area fill out our Quote Comparison Request form to get an instant comparison of prices, products & warranties.

      For a 3-phase connection, installing a system with a 3-phase inverter is usually the most straightforward & beneficial approach. Although it might cost you a little bit more than a system with a single phase inverter, you are likely to be happier with its performance in the end. Make sure you have a chat with installers about your options & best approach as well (i.e. always get a second – or third – opinion).

  2. HI, we have 3 phase power in our home, firstly I have quoted for $4000 for 5 KW with 24x260kw single phase , After some time consultant came back to me and said you need 3 Phase inverter you have to pay for Extra $400, and now its time for installation sent me an new quote with same price 275KWx22, I am realy confused , They are not explaining properly about changing the quote over again , please suggest me some one about this.and then they took deposit before agree the contract at first and keep on changing the things,

    1. Hi Malli,

      As for the extra charge for the 3-phase inverter, that’s par for the course. It’s not very professional (and clearly confusing for you) that they’re changing things up on you at the last minute without explanation. The difference between the two solar panel array configurations isn’t huge (24x260W = 6,240W or 6.24kW, and 22x275W = 6,050W or 6.05kW – so a difference of about 200 watts, or less than one panel). Nevertheless, the reason for the change should be explained to you – or maybe you can ask for an additional panel, which you’d hope they would provide for free in light of the original quote.

      We’d suggest trying to hash things out with them until you’re happy, but if they’re being difficult and you can’t reach an agreement, you might to ask for your deposit back – or worst case scenario, take them to the ACCC.

  3. I have a single-phase solar system (7.5kW) and a three-phase grid connection using a single meter.
    Can somebody please explain what happens in a net metering scenario if e.g. phase 1 with the solar system hooked up to it exports 5kW while at the same time the other two phases consume each 3kW.
    Is the balance to be paid for 1 kW (3+3-5) or do I pay for 6kW (3+3) and a get a feed in payment for the 5kW.

    1. Hi Wolfgang,

      We’ve reached out to our friends at Solar Analytics to get an answer for you. Here’s what they had to say about your comments:

      Technically that is correct – the load and generation is netted out across all of the phases. So, if its all generated on 1 phase, and only consumed on the other 2 that’s ok. Simplest way to think of it is that the bill aggregates all phases, so you can expect generation and consumption to also be aggregated. Ultimately, the exact details of the meter type and tariff type will influence things so the key is to get approval and confirmation from the network company and the retailer.

      Hope this helps!

  4. Hello, I have a single phase 1.5kw solar system. I want to add 30 more 270w panels and go off grid with batties. Can I go 3 phase if not what do you reconmend.

  5. Hi,
    Ive been told you can no longer get 3 phase inverters for domestic use as the exceed 600vdc is this true.

    Regards Owen

    1. Hi Owen,

      That question is a bit out of our league – this article is intended as a basic overview of single vs 3-phase power connections. Please contact your electricity retailer or network company.

      Best of luck!

  6. is it rue that if you have 3 phase power supply in Victoria, it doesn’t matter if the solar inverter is single or 3 phase. Victoria’s polyphase metering means that you only pay the net import or get credited for net export of electricity.
    Appreciate if you could confirm the advice I have been given above.

    1. Hi Keat,

      Yes, that is our understanding as well. Please see the comment from Wolfgang here and our response.

  7. Hi Team
    Have a 5.1 kW PV system with a M6A Grid Invertet that has produced 7070 kWh after 317 days.The grid power to house is 3 phase.Would like to add a hybrid battery bank Hoping to use the quality technologies available but economics taken into consideration.Availability and cost indication would be appreciated
    Regards
    David D.

    1. Hi David,

      I notice that you’ve got a .co.nz email address. Are you looking for a system in Australia (we only service Aus).

      If you are, please just give us a ring at 1300 78 72 73 to discuss your options directly, or you can fill out the Quote Request Form to the right of this page (click ‘battery only’ unless you want to add another PV system).

  8. Hi solar choice staff.
    We have a 2 phase connection to our house (with a single spinning disc 3 phase meter). Would the reasoning above for connecting to 3 phase supplies equally hold for our situation on 2 phase?
    Thanks, Peter

    1. Hi Peter,

      We don’t come across 2-phase quite as much as 3-phase, so I’d advise getting in touch with an electrician or solar installer about it. But I imagine that the same reasoning should hold.

      Best of luck!

  9. After detailed analysis of several electricity retailer’s invoices and inverter output readings for a number of three phase supply/single phase inverter installations in SE Queensland, I have come to the conclusion that there are two different metering programs in use:

    1. Installations that have a feed-in tariff greater than the import tariff are programmed to use the single phase system ie the export is the excess energy generated over that consumed by one phase only, the one the inverter output is connected to. This amount displays as register 40. These are the older installations (before July 10, 2012) which have a mandated feed-in tariff of 44c/kWh minimum until July 1, 2028. The inverter output is best connected to the phase with the least daytime usage.

    2. Installations that have a feed-in tariff less than the import tariff generally have a single multiphase meter which is programmed to use the three phase aggregate system. The energy exported is the excess energy generated over that consumed by all three phases in total, even though the inverter output is connected to one phase only. These are installations after July 10, 2012 and which now have zero mandated feed-in tariff. However, retailers do offer varying feed-in tariffs up to 11c/kWh. It is irrelevant to which phase the inverter output is connected.

    Both of the above programs provide the greatest dollar benefit for the consumer which is the intention of the Queensland Government Solar Bonus Scheme. Both scenarios 1 & 2 could be inadvertantly misprogrammed by the meter installer resulting in a lesser benefit for the consumer.

  10. hi,
    we have solar 3kw on a single phase of a 3 phase system. we want to add another solar system and battery backup on one or both of the other 2 phases.
    we want to be able to isolate (island) the grid in the event of loss of supply and run off the battery backup.
    most of the house is on the single phase that’s currently connected and only under floor heating on the 3 rd phase. whats required for this?

    1. Hi Frank,

      It’s probably best to speak to an installer about your requirements directly. We can put you in touch with some if you give us a ring on 1300 78 72 73 or complete the Quote Comparison Request form to the right of this page.

  11. Hi James. We have just bought a small farm in Sth Gippsland and want to confirm if we can install a suitable pv solar system on the house, which has single phase power supply. Are you able to advise us? Regards, Michael.

    1. Hi Michael,

      There may be some restrictions (esp regarding solar system size) from the network company that services your home, but there’s no reason to think you might have problems because of the fact that you’re on a single-phase connection. Check with an installer who has experience working in your area.

    1. Hi Abdul,

      Possibly, but can’t imagine why it would be a good idea. Best to consult with an accredited installer about the wisdom of doing so.

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