Transmission lines

Solar system size limits: How much does your local network allow?

by James Martin II on September 20, 2017

in Useful solar tools and resources,Solar system sizes,5kW,ACT,NSW,NT,QLD,SA,TAS,VIC,WA

What’s the upper limit to the amount of solar panel capacity that you can put on your roof? This is actually a multi-layered question that involves your roof area, your energy saving goals and any applicable restrictions imposed by your local electricity network company. This article touches on all these factors, but focuses mainly on the issue of how the ‘grid operator’ in an area handles systems over a certain size.

Some quick notes about solar system sizing

Up to 5 kilowatts (kW) is standard these days

If you’re considering solar (or a solar system expansion) for your home, you’ll want to know what the best size system for your circumstances would be. We’ve written extensively on this topic (resources below), but as a rule of thumb a 5kW solar system is both affordable and suitable for most households. A system of this size will generally produce plenty of energy – usually with enough ‘surplus’ solar energy to charge up a battery bank if you choose to install one at a later date.

Even without batteries, any solar energy that you do not ‘self-consume‘ directly within your home will earn you solar feed-in credits on your electricity bill, so it’s not a big problem to have a system that is generating more energy than you need.

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The times we would generally recommend going smaller than 5kW would be when you’ve got insufficient, unshaded roof space available or where your budget doesn’t allow going for a larger system. Additionally, if you know that the energy consumption levels for your home are extraordinarily low, a smaller system (2kW or 3kW) might be more appropriate than 5kW.

5kW+ also appropriate for many households

Although 5kW is the most popular system size going in around Australia at the moment, there are plenty of systems that go above this limit as well. By all means, if you have enough electricity demand and the budget for a 5kW+ solar system for your home, you should.

Resources for selecting the right solar (and battery) system size:

Why are there limits on grid-connected system sizes?

If your home is connected to the power grid, then whether you realise it or not there is a ‘network company’ servicing your home. More accurately, the grid company is known as the ‘distribution network service provider’ (DNSP). DNSPs are by their nature monopolies, as they own & operate the physical infrastructure (‘poles & wires’) that delivers electricity to your home.

Things can sometimes get a bit confusing when it comes to this topic: In some regions of Australia (e.g. regional Queensland & Western Australia) , the network company is also the company that sells you electricity (aka your electricity retailer) but in most cases it’s not (e.g. NSW, Victoria, and southeast Queensland).

How electricity is transported. (Image via AEMO. Click to enlarge.)

The electricity grid as we know it was designed to work unidirectionally – electricity is generated at large, centralised generators (which are more often than not coal plants), sent long distances over transmission lines before being stepped down to distribution lines and finally delivered to your home or business.

The original architects of our electricity infrastructure did not intend for electricity to move in the other direction. While this doesn’t necessarily mean that it’s impossible for electricity to flow backwards, it can potentially be tricky for the networks to manage on a technological level – especially when there are a lot of distributed systems all feeding back to the grid in the same area.

This is the main reason why networks put limits on system sizes, at least until such a time as the grid gets a lot ‘smarter’ and better at handling bidirectional electricity flow.

What are the size limits?

As a general rule (and as per the new AS/NSZ 4777 standard) most networks will allow system sizes as per the below:

  • Single phase connection (most homes): Up to 5 kilowatts (5kW, or sometimes listed as 5kVA)
  • Three-phase connection (some homes and many businesses): Up to 30kW (30kVA)

In essence, most networks will have some kind of ‘pre-approval’ scheme by which your connection will be automatically approved as long as it meets certain requirements – including system size/capacity – which may differ from network to network.

Ultimately, the size limits prescribed by networks may not necessarily be set in stone. It may be possible to get a larger system approved for your home, although there will almost inevitably end up being more red tape and longer wait times involved – not to mention possible extra fees.

Another important implication of size limitations is solar feed-in tariff eligibility. Systems over a certain size may be approved for installation, but not for exporting energy to the grid – which means no solar feed-in tariff benefit. This in turn means that the household in question should do everything they can to ‘self-consume‘ as much solar energy as possible to ensure that none of it is wasted.

Rules may vary – Ask questions

However, the exact implementation of these rules differs from network to network, and from area to area within certain networks. There are a few important ways that the rules can differ, prompting a range of questions to be asked. You can either ring up your local network company, your electricity retailer or just have a chat with some installers about your options.

The questions to ask include:

  • Does the limit apply only to solar inverter capacity, or also battery inverter capacity?
    • Modern, grid-connected solar systems automatically ‘export’ surplus solar energy into the grid, but battery systems with their own dedicated inverter are not strictly designed to do so. Some networks therefore do not count any battery inverter capacity towards the maximum size limit – but most of them do.
  • Will you be required to install ‘export limiting’ / ‘export control’ technology on your system? How about ‘solar smoothing’?
    • The problems that networks have with grid-connected systems have to do with solar going into the grid and disrupting electricity quality in the local network. One solution for this is to require ‘export limiting’ functionality, which prevents your system from putting solar into the grid over a certain threshold (e.g. 3kW limit for a 5kW system) – or in some cases, preventing export altogether. This sort of control is possible with some inverters or with a bit of third-party equipment specifically designed for this purpose. (You may also hear it referred to as ‘grid protection’.)
    • In some networks (the most notable example being Horizon in WA), it is also necessary to install a ‘solar smoothing‘ device – essentially a small battery bank that prevents sudden peaks and troughs in solar system output due to passing clouds. These sudden spikes and dips can wreak havoc on the ‘thin’, spindly grids common in sparsely populated regional areas; a smoothing device helps make them more manageable.
  • Is the limit a ‘hard’ limit – or are there ways around it?
    • In many cases the network may allow you to install a larger system than their standard rules would ordinarily dictate – provided it meets certain additional criteria. This criteria may involve export limiting or even that you pay for upgrades/changes to the physical network infrastructure in your area.

Coming soon: Solar system capacity limitations & requirements by state & network

We’ve been in touch with all of Australia’s distribution network operators and will soon be publishing their system sizing requirements and limitations in a table here. Stay tuned!

State Network Single phase limit 3-phase limit Notes  Additional resources 
ACT ActewAGL
NSW Ausgrid
Essential
Endeavour
QLD Energex
Ergon
NT (Darwin) PowerWater
SA SA Power Networks
TAS Aurora
VIC United
Citipower / Powercor
Jemena
Ausnet
WA  Synergy
 Horizon

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© 2017 Solar Choice Pty Ltd

James Martin II

James Martin II

Communications Manager at Solar Choice
James has been Solar Choice's primary writer & researcher since 2010. He lives in Newcastle in a house with a weird solar system.
James Martin II

{ 5 comments… read them below or add one }

Joachim Staats September 28, 2017 at 2:37 am

I have had rooftop solar since 2008 and am now considering home battery. When I saw the term ‘export limiting’ in the article I was dumbfounded. I had never heard of this before. Some 1.7 million households now have rooftop solar and home batteries are a logical extension. Could ‘export limiting’ really come into play?

Reply

Solar Choice Staff September 28, 2017 at 6:35 am

Hi Joachim,

Unfortunately, yes that is currently what the networks are proposing and in most cases implementing, especially for larger systems. It has to do with managing power quality on the grid – as mentioned in the article, the grid was not set up to be bi-directional. We’re hoping that in the grid of the future all solar system owners will have the unfettered ability to export all the energy they want, though!

Reply

ian garradd September 25, 2017 at 9:10 am

I tend to go along witht eh advice from the ATA and others- that with the new FITs, the bigger the system the better. – regardless of the amount of self- consumption.
also,
if you have an electric hot water system, then that is an excellent storage device to maximise onsite consumption- as long as the HWS is switched over to day raite- and disconnect the off- peak meter.

Reply

Andrew Coffey September 22, 2017 at 2:18 pm

5 kW should be considered a minimum these days. Many solar installers will suggest that 5 kW is the maximum size, but this is simply not true.

Reply

Solar Choice Staff September 25, 2017 at 3:35 pm

Hi Andrew,

By ‘maximum’, I’m more trying to hone in on what networks will allow without extra approvals. Will be updating the table in this article soon, as most of the networks have now responded to my queries.

Reply

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