HOW MUCH ROOFTOP SOLAR POWER CAN YOU INSTALL? – A STATE BY STATE GUIDE

There are limits to the size of the solar panel system you can install on your rooftop. Naturally, there is only so much weight your roof can support! But a less obvious limit sets how much energy your rooftop solar power panels system is permitted to generate.

Rooftop solar power panels: how many can you install? Solar domestic power increasingly popular.

Large increase in rooftop solar installation reduces power bills for Australian consumers. Image: Pixabay

This figure varies – your electricity retailer imposes restrictions on solar power capacity depending on where you live in, sometimes even which town you live in!

These two factors – the number of solar panels and their power output – are also affected by how much clean energy you want to generate for your home or business use.

Let’s look at the factors involved in limiting your solar power while exploring the levels of energy you can achieve in your area.

Why does the electricity retailer set limits?

Technically, it’s not your retailer setting the limits on how many rooftop solar power panels you can install. The limits are actually decided by the owners of the network that distributes the electricity – the poles and wires, also known as the distributor. Confusingly, in some cases your energy retailer also owns the network too – Energex in Queensland, for example.

Electricity transmission towers are owned by the distributor

Electricity transmission towers

Limits on your solar generating capacity are set by companies like Energex because the electricity distribution network was originally set up to push power in one direction only and at a predictable rate. When wind and solar power came along there was a disruption in this traditional network model: the consumers became producers, they wanted to feed their energy into the network.

This two-way model of energy distribution is a people’s revolution in energy. It’s great for the environment and great for the hip pocket.

But the owners of the networks are concerned that too much electricity flowing into the grid could disrupt the operation of the gas and coal-fired power stations that still exist. For example, the grid needs to be kept at a certain voltage. Too much solar input pushes the voltage up and creates problems.

What’s needed is smarter technology that regulates the influx of clean energy so that it can co-exist with the older types of generators. That technology is not quite at the stage where solar power can be added to the grid without limit. But it’s only a question of time until the regulators work out a way to tap into the excess electricity of every rooftop solar system. Already, neighbours are sharing electricity in some areas, cutting out the energy retailer completely.

What are the current limits for solar installation?

Unless otherwise specified, states and territories give automatic approval to rooftop solar power panels systems that comply with the Australian standard for solar installation: 5 kW or under. In most states and territories, there is automatic approval given to any solar system up to 5 kW. However, this is in not set in stone.

For example, in May 2017 the Queensland Government (which owns retailer Energex) changed the regulations for solar installation limits. Automatic approval for rooftop solar used to stop at 5 kW, but the new rules give approval for up to 10 kW.

The proviso is that you are not permitted to have a battery system capable of feeding power into the grid. The government was fearful of a blowout in their feed-in tariff budget, which originally did not allow for batteries. Feeding power into the grid from storage batteries during the night would have proved too costly for its feed-in tariff scheme.

The AS/NSZ 4777 standard allows most networks to allow system sizes on a single phase connection up to 5 kW. Three phase connection size is up to 30 kW.

As long as your rooftop solar power panels system meets the requirements the requirements of your network, you will have no problem getting pre-approval.

But you should speak with your solar installer about what you can and can’t do. For example, in Western Australia, electricity retailer Horizon allows the installation of rooftop solar depending on which town you live in and provides a handy calculator.

The following table shows the limits for automatic pre-approval for solar panel systems by state/territory and energy retailer. Figures quoted are inverter limits.

ACT

ActewAGL

Single phase: 5 kW

NEW SOUTH WALES

Ausgrid

Single phase: 5 kW

Essential

Single phase: 3 kW (rural)
Single phase: 5 kW (urban)

Endeavour

Single phase: 5 kW
3-phase: 30 kW

NORTHERN TERRITORY

PowerWater

Class 1 – Private/residential:
Single phase: 5 kW
3 phase: 7 kW (10 kW per phase inverter limit)

Class 2 – Private/residential & small commercial:
3 Phase: 30 kW with zero export limiter inverter (10 kW per phase inverter limit)

QUEENSLAND

Energex

Up to 30 kW, however all solar installations subject to application process Ergon

Single phase: 5 kW
3-phase: 15 kW

SOUTH AUSTRALIA

SA Power Networks

Single phase: 5 kW
3-phase: 30 kW

TASMANIA

Tas Networks

Single phase: 5 kW
3-phase: 30 kW

VICTORIA

United Energy

Single phase: 10 kW
3-phase: 30 kW

CitiPower

Single phase: 5 kW
3-phase: 30 kW

Jemena

Single phase: 10 kW
3-phase: 30 kW

AusNet

Single phase: 5 kW
3-phase: 15 kW

Western Australia

Western Power

Single phase: 10 kW
3-phase: 30 kW

Horizon Power

Eligibility to install rooftop solar depends on which town you live in – use calculator.

Feed-in tariffs, state by state

There are rebate schemes to encourage solar users to feed electricity into the grid from their rooftop solar power panels. You can find out about them on Energy Matters’ feed-in tariff page.

Otherwise, here are the contact numbers to find out about the latest feed-in tariffs in your area:

  • ACT: Environment, Planning and Sustainable Development Directorate, 13 22 81
  • NSW: Division of Resources and Energy, 1300 736 122
  • NT: Department of the Chief Minister, (08) 8999 5511
  • QLD: Department of Energy and Water Supply, 13 43 87
  • SA: Department of State Development, (08) 8226 5500
  • TAS: Department of State Growth, 1300 135 513
  • VIC: Department of Environment, Land, Water and Planning, 136 186
  • WA: Public Utilities Office (08) 6551 1000

Rooftop solar power panels system sizing

As mentioned previously, up to 5 kW seems to be the current accepted capacity for solar dictated by most electricity retailers.

Regardless of that limit, to get the very most out of your rooftop solar power panels you should consider having the system linked to a battery. That’s because most of a typical family’s energy consumption occurs after work and school hours. So during the day while your panels are busily making electricity, that electricity is going into the grid at a feed-in tariff that is usually a lot less than the retail price you will pay when you really need the energy. It’s more effectively used to charge your home battery. Note that batteries raise significantly the investment that you need to make initially and will increase the time it takes for your system to pay for itself.

Size matters but so does value and a battery can add to your payback time

One of the best ways to gauge the size of the solar system you need is to have a look at your power usage on your electricity bill. According to the Clean Energy Council, a typical Australian house consumes around 18 kilowatt hours (kWh) per day. So a 1-2 kW solar system displaces an average of 25-40% of the average electricity bill.

Considering that today’s average size for a solar system is 3 kWh, it’s possible in some cases to virtually eliminate power bills with the right solar system, battery storage and smart inverter.

How much sunlight is available?

This Clean Energy Council table below shows how much energy you can expect to generate from the sun using rooftop solar power panels in Australia’s capital cities.

The power output of a solar PV system depends on its efficiency, size and location. The table below shows the average daily production of some common grid-connected systems throughout Australia.

City 1 kW system 1.5 kW system 2.0 kW system 3.0 kW system 4.0 kW system
Adelaide 4.2 kWh 6.3 kWh 8.4 kWh 12.6 kWh 16.8 kWh
Alice Springs 5.0 kWh 7.5 kWh 10.0 kWh 15.0 kWh 20.0 kWh
Brisbane 4.2 kWh 6.3 kWh 8.4 kWh 12.6 kWh 16.8 kWh
Cairns 4.2 kWh 6.3 kWh 8.4 kWh 12.6 kWh 16.8 kWh
Canberra 4.3 kWh 6.45 kWh 8.6 kWh 12.9 kWh 17.2 kWh
Darwin 4.4 kWh 6.6 kWh 8.8 kWh 13.2 kWh 17.6 kWh
Hobart 3.5 kWh 5.25 kWh 7.0 kWh 10.5 kWh 14.0 kWh
Melbourne 3.6 kWh 5.4 kWh 7.2 kWh 10.8 kWh 14.4 kWh
Perth 4.4 kWh 6.6 kWh 8.8 kWh 13.2 kWh 17.6 kWh
Sydney 3.9 kWh 5.85 kWh 7.8 kWh 11.7 kWh 15.6 kWh

The rated output, e.g. 4.0kW, is that achieved in perfect lab conditions. The table above takes real wold conditions into account when predicting averages for any given system.

Panels generate more electricity in summer than in winter. The table above reflects the electricity generated averaged across the whole year.

A typical Australian house consumes around 18 kilowatt hours (kWh) of electricty per day. This means that a 1-2 kW system could displace 25-40 per cent of your average electricity bill.

It shows that in Brisbane a 3 kW solar system will on average generate 12.6 kWh daily, or 70% of an average household’s daily power usage. In Melbourne – a city that is on average less sunny than Brisbane – the same 3 kW solar system would generate 10.8 kWh daily (60% of daily usage).

This shows that with batteries to store the excess solar power you generate, it is possible to supply a substantial amount of your home energy needs as long as the correct sized system was installed.

Other questions you could ask about your solar system include:

  • Does the limit laid down by your electricity retailer apply only to solar inverter capacity, or also battery inverter capacity?
  • Are you limited on how much electricity you can feed back into the grid from your panels?
  • Will you need a solar smoothing device? These iron out the fluctuating energy output of your panels as a result of changes in the weather.

The best way to find out the ins and outs of rooftop solar power panels installation, which can seem more complicated than it really is, is to get in touch with Energy Matters in your area and talk to one of our consultants about a quote or call 133 786.

Only they will be able to tell you about the latest rules and limits on your solar installation. Inside information from Energy Matters’ experts will make sure your system is the best you can afford, while remaining within the regulatory framework laid down by your electricity retailer.