3 Phase Solar System : What you need to know about connecting solar to your 3 phase supply

 

Solar is compatible with 3 phase

There is an awful lot of confusion (and misinformation) out there about the practicalities of installing solar on a house that has a 3 phase supply. So I’ve written this post to clear up the confusion.

Connecting solar power to a 3 three-phase supply is entirely possible. But you need to decide how you are going to connect your solar system to the grid. Your 3 options are:

1) connect your solar system to only one of your supply phases with a single-phase solar inverter.

2) connect your system into all 3 phases of your supply with a single, 3-phase solar inverter

3) connect your system into all 3 phases with 3 separate single-phase inverters.

Here’s what you need to consider in deciding which option to go for:

Three phase billing

Now that Feed in Tariffs are generally between 6 and 10c per kWh, compared to an electricity price of 30c or more, naturally people installing solar want to self-consume as much of their solar energy as possible and minimize the flow of exported solar electricity.

So most of the emails I get these days about 3 phase worry that if they choose option 1 they will lose out. They worry that any electricity they use on the 2 phases that are not connected to solar will all be imported at 30c per kWh no matter how much solar they are generating on the solar phase.

I have personally never seen an installation where this happens. All the 3 phase meters that I have seen take into account the sum of all the electricity being used on all the phases and then subtract that from the amount of solar energy being generated to calculate the import or export amount for billing. i.e. if you are on a stingy FiT, they don’t penalise you financially for having a single-phase inverter on a 3 phase supply.

But to muddy the waters, I have seen evidence and heard from some installers that say they have seen 3 phase meters that have been configured to only calculate exports based on the solar phase. So buyer beware!

Three-phase load balancing

Having said the above, it is important to note that it is not unusual for the demand across phases to be unbalanced; i.e. a lot more load on one or two of the phases. For solar financial payback, this is less of an issue (due to the summed billing) however, from a technical perspective, balancing consumption and generation across the phases is a good thing for power quality.

I have seen cases where voltage is problematic on a particular phase causing inverters to trip out; such as where a large pump or cool room is on that phase and presents high start-up demands. In such a case, you should consider putting the inverter on a more stable phase; they don’t like unstable voltage or frequency at all.

Ultimately, a bit of instantaneous and energy consumption demand analysis should be considered a prerequisite to connecting solar to three-phase systems. Your utility or perhaps a friendly solar installer can help with this. If you have three-phase, it is even more important that you choose a qualified solar installer to talk to initially, instead of a less qualified solar salesperson – who probably hasn’t got the electrical background to understand the nuances of multi-phase electricity supplies! 

If you have a 3 phase supply, should you get a three-phase or single-phase inverter?

3 phase inverters start at about 5kW so if you want an inverter smaller than 5kW you are looking at single-phase.

If you want a system with an inverter larger than 5kW then your local Electricity Network may insist that you use more than one phase. The best way to do this is to use a 3 phase inverter.

If you want a solar system with a total inverter capacity larger than 15kW (5kw per phase) then the relevant Australian Standard (AS4777.1:2016) says you must balance the phases. The easiest way to do that is simply to use a 3 phase inverter.

If you have skinny wires from your meter to the grid, then you may have a problem with high voltage drops. If the voltage drop is too high, you may not be able to install solar. A 3 phase inverter spreads the power across 3 phases, so makes the voltage drop on each wire 3x smaller. So if you have an issue with voltage drop – a 3 phase inverter is a good solution.

Otherwise, if you are installing a system and have the choice of one single-phase meter, or one 3 phase meter, the choice is yours. The advantage of a 3 phase meter is that it is a more robust system (lower voltage drops, phases balanced). The disadvantage is that is about $600 more for a 3 phase meter. I’d pay the extra personally.

Advantages of 3 Phase Solar

If you are researching about solar power system, you may have heard of different types of solar inverters especially single phase and 3-phase inverters. Depending on your electricity supply (single-phase or 3-phase power) your decision might become simpler. In most Australian homes, the power supply is single phase, which means one live wire comes in from the grid. Single-phase power supply is commonly used in Australian homes while three-phase power supply pulls more power from the grid and is useful to handle bigger loads for large aircons, pools, heaters, electric car chargers, etc.

Do you have a 3 Phase Power supply?

Check your switchboard - If the main switch is one-pole wide, then your home is connected to a single-phase power supply. If the main switch is 3 poles wide, you have 3-phase power.

Alternatively, you can call your electricity provider and ask them about the power supply. Just keep a copy of your electricity bill handy.

Check the service fuse - Homes connected to a single-phase power will have one service fuse while for a 3-phase power supply, there would be 3 service fuses.

Most of the homes are connected to a single-phase power supply. Large homes, residential apartments and commercial buildings can have a 3-phase supply to manage the high electricity demand.

3-phase power is good to handle heavy loads from:

·        Spa

·        Sauna

·        Pool heater

·        Electric car charger

·        Ducted air conditioners

Single Phase vs 3-Phase Solar Inverter

A single-phase solar inverter has one live wire which connects to your home. While a 3-phase solar inverter has 3 live wires connected to your home.

A 3-phase solar inverter sends the electricity evenly across the 3 wires which minimizes the voltage drop problem associated with a single phase power supply. It needs to be noted that a 3-phase solar inverter will probably cost more than a single-phase inverter.

So should you buy a single phase or 3-phase solar inverter?

A single-phase inverter usually comes in a capacity of less than 5kW. But if you are looking for an inverter larger than 5kW, and you have 3-phase power in your home then a 3-phase solar inverter is ideal. If you have a single-phase power supply, you only need a single phase inverter.

For a 3-phase supply the best solution is to go for a 3-phase inverter. However, if your solar power system is less than 5kW, go for a single-phase inverter.

Benefits of 3-Phase Solar Inverter

The 3 phase inverters come in a capacity of more than 5kW, up to 30kW which allows users to install a high capacity solar system.

3-phase solar inverters manage voltage rise and reduce the chance of appliance failures due to high voltages as the voltage rise in a single-phase connection is higher than that of 3-phase power. By using a 3-phase connection, the power supplied to the grid is distributed evenly and leads to grid stability.

 It increases the local grid voltage and your circuits will have less chance of short-circuiting due to high voltage issues.

If a 3-phase inverter is chosen, the consumers can meet their energy demands easily reducing their dependence on the grid for energy and leading to reduced utility bills.

3 Phase Solar Inverters: Do you need one?

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:

Under the circuit break named “Main Switch” does your switchboard have one breaker or three breakers?

Is there one or three wires leading from the electrical transformer on the street to your home?

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.

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 minimize 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 optimize 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 system inverter

Pros of a 3 phase solar inverter	Cons of a 3 phase solar inverter
Minimize voltage issues on grid Minimize 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)

 

How do you know if you have 3 phase power?

There are a few ways to know this, by looking at your:

·        Main switchboard

·        Overhead main

·        Meter

·        Isolation link

Main switchboard

In some countries, a switchboard is referred to as the main electrical fuse, as the fuses are organized together with the main power lines.

Electrical fuses help to prevent major damage to your home when there is a huge surge of electricity as well as separate incoming electricity into different circuits in the house.

When you look at your switchboard, you will see a row of panels or switches, sometimes referred to as ‘poles’. The supply lines in newer switchboards are sometimes red in colour.

Count the ‘poles’. If you see three poles joined by a single bar, you have a 3 phase. In a switchboard of a 3-phase supply, you are forced to switch all the live wires off or on simultaneously by pushing the bar that joins the switches.

If you see only one ‘pole’, then you have a single phase. Homes with 2 phase supply have 2 poles linked by a single bar.

It is also possible to have 3 switches but only a 2 phase supply. In this instance, you may need to check the meter or iso-link.

Overhead mains

A 3 phase supply can also be indicated in the number of cables connected to the house. They can be seen hooked up near the roof of the building. The ‘point of attachment’ will show a bundle of 4 cables – 3 cables for 3 phases of live wires and 1 neutral cable.

If you see only 2 cables, it means there is only a 1 phase supply because one cable is always allocated for the neutral cable.

Meter

There are many types of three phase meters. Some are digital, and some are not. For the non-digital ones, count the ‘poles’ on the meter isolator. If you see only one pole, it is a single phase meter. The sample image below is for a 3 phase supply.

If it is a digital meter, you’ll need to look at the display. A 3 phase meter will show L1, L2 and L3.

In some countries, the phases are not so easily identified through the meters.

Isolation links

Often referred to as ‘iso-links’, they are a relatively new electrical technology having only been around from 2011. This component is meant to disconnect power from the electric meter in case the meter itself needs to be replaced. 

Not every house may have an iso-link. If it does, the number of iso-links will indicate the number of phases.

What are your solar options if you have a three-phase supply?

Your options are:

a single phase solar inverter

microinverters 

a three phase solar inverter

All of them are valid options but there are additional benefits for the last one, which will be explained in the next section.

When deciding whether to opt for a single phase solar inverter or a 3 phase, you’ll need to understand these two things first: three phase billing and three phase loading.

Three phase billing

The reason most people have solar installations for their grid-connected home is to reduce the cost of their electricity bill by harvesting free solar energy. The incentive for doing so is even greater in countries which have Feed in Tariffs (FIT).

Naturally, people would want to use as much solar-generated electricity as they can and reduce paying the higher rates of grid-powered electricity. However, there are some concerns that a 3 phase solar inverter will affect billing.

What really counts when it comes to billing is the meter. A house with a 3 phase supply will have a 3 phase meter. The meter will take into account the sum of all the electricity being used on all the phases. Then, subtract the amount of solar-generated electricity for export.

Three phase load balancing

The issue of load balancing is a real one. Meaning, one phase has a bigger voltage load than the other two phases.

Having a balanced load across 3 phases of supply is good for power quality. There must be a balance between power generation and consumption. An imbalanced load on one phase can cause the inverter to trip.

Say you have a phase that supports a large swimming pool pump which has a high start-up demand. If the demand for electricity is higher than the supply, it creates an imbalance in the phase and could force the inverter to trip. Inverters generally don’t function well when there is unstable voltage.

Since analyzing the energy consumption demand of your household for a 3 phase system can get quite complicated, it is best to engage a trustworthy and qualified solar installer who is familiar with the nuances of multi-phase electricity supply.

Benefits of a 3 phase solar inverter

The main benefit is that a 3 phase solar inverter can feed electricity evenly into all 3 phases of a property. To better explain this point, let us compare it with the workings of a single phase solar inverter for a 3 phase supply.

A 5 kW single phase solar inverter working at maximum capacity would feed 5kW of solar power into one of the three phases in a property. However, a three phase 5kW solar inverter would divide the 5kW equally into 3 phases. Each phase of the property will receive 1.7 kW each.

The difference matters when the solar power system can generate more electricity than can be handled by a single phase. For instance, if a system produces over 6kW and feeds all of that into one phase, this may cause an overload of that phase.

When an overload occurs, it could trip the circuit of that phase, and you will experience an interruption in electrical supply instead.

Is it cheaper to run on 3 phase solar inverters?

Depending on the country or source which you buy a 3 phase solar inverter from and the brand, it can cost you $300 more than an equivalent single phase solar inverter. 

A 3 phase solar inverter also has to be run with a compatible solar battery, which may be an additional cost to you if you don’t already have one.

Can I get 3 phase power in my home?

Yes, but if your home does not already have 3 phase supply, it can get extremely costly. If you are building a new home, installing a 3 phase inverter won’t cost you much more.

The electrician only needs to pull a couple of extra cables to your switchboard while he is doing the wiring. If done correctly, it will minimize the impact of voltage rise, and it will also allow you to install a much bigger solar electrical system.

Conclusion

Three phase solar inverters have the one up over single phase inverters when it is installed in a solar system on a property with 3 phase supply. Its advantage is that it splits the AC converted electricity from the solar panels into three batches each time. 

When the divided load is fed into the property, which is connected to the power grid, there is little to no likelihood of a voltage rise occurring. 

This is because the split AC amount is minimal compared to the total AC flowing in from a single phase solar inverter. A 3 phase solar inverter, thus, guarantees a smoother and uninterrupted power supply since it does not trip the grid with voltage overload.