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
6.6 kilowatts (kW) is the most common system size 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 6.6kW solar system is both affordable and meets most of Australia’s network requirements for a simple approval process and permission to export (receive a feed in tariff). 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.
The times we would generally recommend going smaller than 6.6kW 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 6.6kW.
Resources for selecting the right solar (and battery) system size:
- Kilowatts vs kilowatt-hours: Power, energy & capacity in solar & batteries
- Solar Choice Solar Payback & ROI Calculator (because selecting the appropriate size has a lot to do with finances)
- What size solar PV system should you buy?
- Solar & battery system sizing: A quick guide
- 5kW vs 3kW solar systems: Which is the better investment?
- Solar Choice Solar & Battery Sizing & Payback Estimator
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.
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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. Sometimes, the feed-in tariff limit is set by your electricity retailer – not the network.
Solar system capacity limitations & requirements by state & network
We’ve been in touch with all of Australia’s distribution network operators in an attempt to work out what the rules are from one network to another. To the extent possible these rules have been verified with each of the networks but many reserve the right to review each connection on a case-by-case basis.
As a general rule, 5kW tends to be the upper system size limit for single-phase connections, but some networks allow up to 10kW. There are lots of variations to this theme, however. Some networks will allow larger sizes than those outlined below, pending specific approval from the network. Some networks count battery inverter capacity towards your total allowable inverter capacity, while at least one network (ActewAGL) does not class battery storage as ‘generation’ and therefore does not. Some networks currently set the limits in terms of kilowatts (kW), while others use kilo-volt-amperes (kVA) – usually based on the inverter capacity, but sometimes on the peak solar array capacity. It’s complicated!
|State or Territory||Network||Description||References|
|ACT||ActewAGL||Single phase: 5kW maximum|
3-phase: Up to 30kWLarger systems require additional technical study before approval can be granted.If the site has single phase supply, the maximum size system that can be installed is 5kW, for 3-phase supply it is up to 30kW.The 5kW limit applies to the AC output of the inverter only. ActewAGL considers energy storage systems, such as battery banks, not to be a source of generation and therefore the 5kW limit does not apply to these systems.Customers who wish to install larger than 5kW on single phase supply must install an export limiting device (either via inverter or additional devices) to ensure that output from the system never exceeds this limit.
|Ausgrid||Small-scale systems limited to 10kW (inverter capacity)|
Installations greater than 10kw but less than 30kw are classed as large scale generation and requires submission of an additional embedded generator connection application. A formal generator connection agreement may be required depending on the size of the generating system.
|Essential||An application for solar connection will automaticall be approved if the system is ≤3kW Rural or ≤5kW urban, and application meets all other requirements.|
At times export limitation may be required because of network constraints.
Inverter capacity limits include battery inverter (if separate from solar inverter).
|Connection to network information pack|
|Endeavour||Single phase: Up to 5kW|
3-phase: Up to 30kW
|Installing a new solar generator at your house|
|Energex||Single phase: Up to 5kVA inverter capacity. 3-phase: up to 15kVA inverter capacity.|
IES systems above 5kVA per phase that intend to export power to the grid will be subject to a technical assessment.
|Connection standard for solar systems up to 30kVA|
|Ergon||Single-phase: Up to 10kVA inverter capacity, but only 5kVA allowed for export. Systems with equal to or less than 3.5kVA inverter capacity will receive automatic approval.|
3-phase: Up to 30kVA inverter capacity, but only 15kVA allowed for export.Higher export limits on both single and 3-phase connections are possible, but will generally require making an application with their retailer to upgrade service to dual phase or 3-phase.
|Connection standard for micro energy generation units|
|NT (Darwin)||PowerWater||For ‘class 1’ small-scale systems –|
Single phase: Up to 5kVA
|Solar PV systems|
|SA||SA Power Networks||Single phase: Up to 5kW|
3-phase: Up to 30kW(Battery inverter capacity is counted towards total allowable capacity.)
|TAS||Tas Networks||Single phase: Systems over 10kW must have export limiting technology|
3-phase: Systems over 30kW must have export limiting technology
|Connecting micro generation systems|
|United Energy||Single phase: 10kW system size limit|
3-phase: 30kW system size limitThese limits are for ‘basic’ connections. Larger systems may be permitted but will require additional technical study before approval can be granted.
|Citipower / Powercor||Single phase: Up to 5kW system size limit (by inverter)|
3-phase: Up to 30kW system size limit (by inverter – 10kW per phase)Depending on the transformer size and existing inverter connections an inverter smaller than 5kW may be required.For three phase transformers, assessment of larger inverter systems can be undertaken; fees may apply.
|Solar and other generation|
|Jemena||Single phase: Up to 10kVA (by inverter)|
3-phase: Up to 30kVA (by inverter – 10kW per phase)Battery inverter capacity is counted towards total allowable capacity.
|Embedded generation – preliminary enquiry|
|Ausnet||Single phase: Up to 10kW system size limit (5kW export limit)|
3-phase: Up to 30kW system size by limit (15kW export limit)Ausnet has an online assessment tool to help customers and installers determine the ‘pre-approval’ limits in their specific area.
|Solar capacity pre-approval|
|Western Power||Single phase: Up to 10kW system size limit (by inverter)|
3-phase: Up to 30kW system size limit (by inverter)Western Power has an online assessment tool to help customers and installers determine the ‘pre-approval’ limits in their specific area.
|Solar, batteries & electric vehicles|
|Horizon||System size limits vary dramatically depending on capacity on the local network. Additional grid protection technology (such as ‘solar smoothing’ and export limiting) may be required for systems in excess of the stated size limits.|
Please refer to feed-in tariff eligibility calculator via link to the right.
|Eligiblity to install solar and buyback schemes|
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.
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© 2017 Solar Choice Pty Ltd
He is now the communications manager for energy technology startup SwitchDin, but remains an occasional contributor to the Solar Choice blog.
James lives in Newcastle in a house with a weird solar system.
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