Single Phase Vs Three Phase For Solar Systems

3 phase vs single phase solar

Do you know what sort or power you have to your home or commercial premises? More importantly, do you really care, and does it matter for your decision about solar power?

Before we talk about how single-phase and 3-phase affects your solar PV connection, let’s clarify what these two power sources mean.

What are single-phase and 3-phase power?

Both single-phase and 3-phase power are used to transmit and distribute electricity.

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

Homes or commercial premises that have 3 live wires coming in from the grid are running on 3-phase power. Commercial premises are likely to have 3-phase power.

What are the benefits of single-phase power vs 3-phase power?

Nearly every appliance in your home will run on single-phase power. This is true regardless of whether you have a single-phase or 3-phase connection

On the other hand, if you have a 3-phase connection, the electricity entering your home or building is divided into three separate ‘phases’ or three cables/circuits. Each of these phases will power different devices.

For example, in a home, your lights may run on one phase, while your swimming pool and air conditioner might be on the second and your washing machine, dryer, and refrigerator on the third phase.

We can look at how 3-phase power is ‘divided up’ for household & industrial loads in the diagram below. In this diagram, you can see that all three phases feed into the industrial motor, while the household appliances like the light globe and power point each receive power by a single phase (represented by the yellow and red lines, respectively).

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

Three-phase power allows commercial premises and homes to pull more power from the grid. The benefits of this are obvious for commercial premises running large manufacturing equipment, and air conditioning units. It is also handy for households that are drawing big loads for things like pool heaters, spas, or electric car chargers etc.

A 3-phase supply means you can send much more solar energy back into the grid. Depending on your local Distribution Network Service Provider (DNSP) rules, this could be three to six times greater than if you are on single-phase power.

What does all this mean for your solar PV system?

If you want to install a solar PV system, you need to know what phase power you are running.

Firstly, your phase connection will have an impact on the size of solar system that you’re allowed to install. Generally, there are more restrictions on the size of the solar system you can install if you are running with a single-phase connection than with a 3-phase connection.

Apart from that, the implications for homes (or potentially even small offices) running with single phase power are straightforward.

If you have a single-phase connection, you should install a single-phase solar inverter. Simple!

On the other hand, if you have 3-phase power, you can choose from several options:

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

The single-phase inverter option

In this option, you can install a single-phase inverter on one of the phases that uses the most electricity or has the heaviest loads.

It’s important to have your solar installer undertake an assessment to determine which phase is the best one to connect the inverter to. This will make sure the solar energy flows where it is needed most (and isn’t wasted) and minimises the chances of the inverter ‘tripping out’ if the voltage for that phase goes too high.

Alternatively, you could install 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. So, if you are considering this, make sure you do your homework by getting comparative quotes.

The microinverter option

Microinverters are small, self-contained inverters that attach to the back of each solar panel and manage the power output for that panel.

Microinverters are more expensive than single-phase inverters systems but also have the advantage of helping reduce power loss from panel failures or shading, letting you harvest the maximum amount of power from your system.

With a microinverter, you can also simply add more panels to your system if you need to expand its capacity in the future. And if one microinverter fails, you only need to replace one, not the entire system.

When installing your microinverters on a building with 3-phase power, you can either put them all on one phase or spread them out over 2 or 3 phases.

Your decision may partly be driven by DNSP limits and rules. But if you have 3-phase power, you can usually install 3x the capacity compared to a single-phase supply.

The 3-phase inverter option

The best and simplest option for homes and commercial premises with 3-phase power may be to get a 3-phase inverter.

The main benefits of a 3-phase solar inverter are that it takes DC electricity from solar panels, breaks it up and evenly sends it out across all three phases as AC electricity.

For example, a 6kW single phase solar inverter working at maximum capacity would be feeding 6kW of solar power into one phase. But a 3-phase 6kW solar inverter would feed the power evenly into each of the 3 phases – so, 2kW of power into each phase.

The downside of 3-phase solar inverters is that they have a higher price tag compared to single-phase solar inverters.

Conclusion

Any of the three options outlined above are valid. Your decision will really come down to how much you can afford, how and where you need your electricity, and potentially DNSP limits.

As with everything in this space, you should seek the advice of a good solar installer and get several quotes to make sure the choice you make is the best one for you.

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