I’ve got 3 phase power but I’ve been quoted for a single phase solar inverter

Fronius Symo InverterThe goal of solar system owners in NSW should be to use as much of the solar power in the home at the time of generation. The cost of electricity has skyrocketed over the last few years; with most households now paying between 25c and 30c per kWh, and yet feed-in tariffs for excess solar power are typically less than 7c per kWh. This means that you don’t want to be sending too much solar power to the grid.

So why then are you getting quoted a single-phase inverter when you have three-phase power? Won’t you still be paying for power on the other two phases? Let’s find out.

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A single phase inverter on a three phase supply

When your solar installation is completed your existing meter needs to be replaced with a new bi-directional solar meter by your energy retailer. If you have three phase power this meter will be a three-phase digital meter, and it will replace your existing meter (or meters if you have three old analogue meters). Typically your new meter will be the Atlas EDMI polyphase meter or similar.

When this meter is programmed, it is done in such a way so that it records the consumption across all three phases before it sees any solar power as surplus. The meter reconciles the three phases and records your total usage as one total before recording any excess solar power.

As an example, you are using 1kW of power on each of your three phases for a total of 3kWs. You have a 5kW solar system that has either a single phase inverter, a SolarEdge single-phase inverter, or an Enphase Micro Inverter system with a single phase connector. At 2 pm on a given day, your system is outputting 4kW of power.

What actually happens is 4kW of power is fed into one phase. You use 1kW of the solar power and 3kW is fed off to the grid. Your other two phases use power from the grid, in this case, a total of 2kW. So you have 3kW going out to the grid and 2kW being used from the grid.

What gets recorded in your meter in this example is firstly a total of your usage across the three phases: 3kW. It will then record any excess solar power, in this case, 1kW. You will not pay for the 2kW that have been used from the grid as it is covered by the 2kW you sent to the grid – a way of explaining this is that they cancel each other out.

To clarify, you have not bought any power from the grid and you will get a feed-in tariff from your retailer for the excess 1kW sent to the grid.

This means that in most cases Solaray will install a single phase inverter for any system that is smaller than 5kW, including our SolarEdge and Enphase systems. It is a waste of money buying an expensive three-phase inverter, as quite simply it adds no additional value.

If you are looking at a system that is 5kW or larger, please contact us for more information. In most cases, you need to have three phase power and we are required to install a three-phase inverter.

The information provided is advice given to the best of our knowledge. All electricity meters are owned by the energy distributor.

Comments

  1. Charles

    If you send 2KW to the grid, you are only getting the feed in tarrif. So we are still paying 30 cents, but getting only 11 cents for the 2 KW feed in, how do they cancel each other out?

    • Solaray

      Hi Charles, so the idea is: if you send 2kW to the grid on one phase, but buy power from the grid on another phase, the meter cancels the two out. So you don’t get paid a feed-in tariff nor do you buy the power on the other phase. The meter reconciles the three phases.

  2. John

    Hello,
    I am trying to come to grips with a single phase inverter on a 4.5 kW system and how the Smart Meter is supposed to do this cancelling bit but my daily usage rate has not varied very much since back in 2009 when I didn’t have any solar at all, it has reduce a tiny bit but I put that down to newer appliances I have purchased as well as LED globes and tubes,I have read that some so called Smart Meters can be programmed as the other chap has stated, I would like to hear your views on this and also a solar installer friend has told me the single phase inverter on a 3 phase system is not very efficient at all.

  3. Cameron

    We are considering upgrading our solar. We have an existing 1.5kw inverter with 8 panels. Our house has three phase power. The existing inverter is connected to phaseA. We have been recommended a second 5kw single phase inverter with 24 panels. Some installs have advised connecting both inverters to phaseA, others have advised connecting the second new inverter to phaseB. Which advice is correct?

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