If You Have Three-Phase Power, Do You Need a ...

Most Australian homes have a single-phase power supply, which basically means they have one live wire coming in from the grid. Some houses, however, have a three-phase supply, with three live wires pulling power from the grid.

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A three-phase home can pull more power in from the grid, which is useful if the house needs to power bigger loads such as large air conditioners, pool heaters, or electric car chargers.

Do you have a three-phase power supply?

To check if you have a three-phase supply, all you need to do is look in your switchboard. If you have a single-phase supply, you will have only one &#;pole&#; on your main switch or meter isolator. If you have a three-phase supply, you will see three &#;poles&#;.

What is a three-phase solar inverter?

A three-phase solar inverter takes in DC electricity from solar panels, converts it and sends AC power through the home evenly across three phases. These inverters generally look the same as a single-phase inverter, although they can cost quite a bit more.

Three-phase solar inverters work best with larger solar inverter systems, as it avoids having too much load being sent out on one single phase, which could cause an imbalance between the loading of all phases. However, this is usually a consideration for 6kW or larger systems, and not so much for 5kW capacity or less inverters, as 5kW of power going through one phase will generally not pose any problems.

Do you need a three-phase inverter?

There are several benefits of using three-phase inverters. Firstly, as mentioned above, these inverters will help to avoid imbalances in the power loading. Secondly, when the inverter capacity is spread across three wires, it would be easier to push the solar energy back out to the grid. Using a three-phase solar inverter in a three-phase supply home can also significantly reduce the occurrence of over-voltage issues.

Having said that, in most cases, a single-phase inverter is sufficient for systems that are smaller than 5kW. For these small systems, a three-phase inverter may not necessarily add extra value. The exception to this is if you are located in a rural location that is far away from the power lines on the street. In this case, a three-phase inverter can be used to raise its preset voltage limits, to push out its generated power back to the grid.

The best way to find out if you do need a three-phase inverter or not is to speak with solar power experts. At Total Solar Solutions, we can do a site inspection to check if your home and power usage will require a single-phase or three-phase solar inverter.

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Most residential premises in Australia have single-phase power, but if you have a large home or have specifically upgraded your power supply (for example to cover a hot-tub!) then you may have 3-phase power or even 2-phase power.

What is 3 phase power?

The more common single phase power has two wires (usually contained in one cable) connecting from the local transformer to your home &#; an active and a neutral. The power supplied through the active cable is 240V which is standard in Australia for all household appliances. 

Three-phase power has 4 wires &#; 3 actives and a neutral. It can supply power at the standard 240V and at 415V for appliances that require greater power like some air conditioners. A three-phase connection effectively triples the power available as appliances can be split across each of the three phases. 

Almost all commercial premises have a 3-phase connection. 

How do I know if I have 3-phase power?

Often this information will be written on your electricity meter, which might be located near the main electrical switchboard for the house. If you can&#;t decipher the electrical jargon on the meter, then you could check one of these things:

1. Under the circuit break named &#;Main Switch&#; does your switchboard have one breaker or three breakers?

2. Is there one or three wires leading from the electrical transformer on the street to your home?
3. Call your Distributed Network Service Provider (DNSP). On your electricity bill there will be the company that sells you electricity and another company (your DNSP) who you can call in the case of power outages and emergencies. If you quote your Net Meter Identifier (NMI) from your bill they will be able to tell you what type of connection you have.

Do 3-phase homes need a 3-phase solar inverter?

The short answer is no, but there are some reasons why you might want to include a 3-phase inverter which usually only cost around $500 more.

If you have a single phase solar inverter it can only be connected to one phase of power. Typically the appliances in a 3 phase home will be split across the 3 phases. That means a single phase solar inverter can only directly tackle a third of household usage. However the smart bi-directional meter (that will get installed with you solar system) will offset any additional energy that is consumed across the other phases before buying any energy from the grid.

For example a 3 phase home has 2kW of usage of power across phases A, B and C and a typical single phase 5kW solar system is connected to phase A. If the 5kW solar system is outputting 4kW of power, then 2kW will be used by directly by phase A and the remaining 2kW will be offset by the smart meter against the other phases.

For more information, please visit three phase battery storage.

In another example, consider if there was only 1kW of usage of power across phases A, B and C and the 5kW solar system was outputting 4kW. In this scenario 3 kW would be offset against the 3 phase home&#;s usage and 1kW would be sold back to the grid.

There is a downside to installing a single-phase inverter on a three-phase home and it relates to the impact on voltage rise. In a single phase system the solar power is working much harder to be used. Without diving into the detail this means that the voltage will rise on the grey line in the above diagram, in some cases this may mean your solar inverter trips off. You should be notified via the monitoring software and can easily turn the system back on, but this can become an annoying problem.

High voltages are one of the main issues network operators (DNSPs) are facing across following the installation of almost 3 million household solar systems. Installing a 3-phase inverter will minimise your impact on the grid. As a result networks usually permit larger systems on three phase connections, which may be an added benefit if you are looking to install an inverter larger than 5kW in capacity. 

Sometimes we see 15kW systems where the solar installer has installed one single phase 5kW inverter on each phase. In the energy system&#;s eyes this is still an inefficient solution as the solar power cannot directly optimise across phases. If phase B draws 10kW then a system with three single phase inverters must draw power from the grid, while a three phase inverter 15kW inverter could tackle the entire 10kW if there was no usage on phases A & C.

Pros and Cons of installing a 3-phase solar inverter

• Minimise voltage issues on grid

• Minimise inverter tripping off due to voltage issues

• Enables a larger solar system size

• ~$500 more expensive

• Can make battery back-up more challenging (read on this below)

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