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How do Single Phase Inverters work

on a Three Phase property?

Resinc Solar

· Solar,single phase,three phase,inverter

It is very common that you may be quoted and provided a single phase inverter for a property that has three phase power. So how does this work? Won’t you still be paying for power on the other two phases?

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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).

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, say your household is using 1kW of power on each of your three phases for a total of 3kWs. You have a 5kW solar system that has a single phase inverter connected to your primary phase. At 3 pm on a given day, your system is outputting 4kW of power.

So the 4kW of power is fed into the one primary phase the inverter is connected to. You use 1kW of the solar power on that phase and 3kW is fed back 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.

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So what happens if you have batteries connected as well?

Batteries will be limited to the single phase they are connected to for both drawn down and blackout protection i.e using the stored power.

In most cases this system setup is still an ideal outcome, as the majority of three phase properties will still have the bulk of the household appliances and circuits on their primary phase to which your battery is connected. While other heavy use items such as pools, three phase air-con, irrigation or mechanical equipment will generally be on the secondary phases. These items often require more current to operate which would in turn, exceed the batteries output capacity and force it to shutdown and you would again have to drawn from the grid for electrically safety reasons.

This is why it’s current best practice to isolate the battery to the primary phase so the household genuinely has a reliable ‘emergency power supply'.

In Summary, single phase inverters can work perfectly well on a three phase supply and it is common industry practice for systems utilising a 5kW inverter or less. However, as with all homes and solar systems, it is always advisable to speak with a professional and obtain an assessment and quote for your unique situation.

For further information, or to arrange a quote for your property today, complete the enquiry form below and one of the RESINC team will arrange for your personalized quote and assessment.