Design considerations

Make sure your rooftop solar system design will meet your needs.

You can tailor the design of your rooftop solar system to meet your needs. The system design will depend on:

  • what you want the system to achieve
  • your current and future electricity use
  • the size and shape of your roof
  • local regulations.

Designing the right solar system for your needs should be a partnership with your solar retailer or accredited installer. You should take your time and shouldn't feel rushed.

Decide what you want from your solar system

Understanding what you are trying to achieve with your rooftop solar system will help your solar retailer or installer design the right system for you.

For example:

  • are you aiming for the lowest possible electricity bill?
  • do you need the system to pay for itself in a few years?
  • how much can you afford to pay upfront?
  • do you want to reduce your carbon footprint as much as possible?
  • do you want a solar and battery system to provide electricity during power outages?
  • do you need a grid-connected or off-grid solar system?
  • will your electricity use increase in the next five years?
  • do you want to add panels or a battery to an existing solar system?

Financial and environmental benefits

The bigger your rooftop solar system, the more electricity it will generate. This means you will need to buy less electricity from the grid and your electricity bills will be lower.

A bigger system will also offset more greenhouse gas emissions and reduce your carbon footprint.

However, a bigger system may cost more upfront and take longer to pay for itself through bill savings.

The most cost-effective system for you will depend on how much electricity your home or business uses and when you use electricity. Consider your electricity needs for both now and in the future. You will get the best value for money by using as much of your solar electricity as you can in your property, rather than exporting it to the electricity grid.

Read more about how solar pays for itself.

Tip: Find out what the most cost-effective system size is for you with SunSPOT.

Back-up supply in a power outage

Many grid-connected solar systems shut down when there is a power outage. Even some battery systems won’t power your property during an outage.

If you live in an area that is subject to power outages, you should let your solar retailer or installer know if you need a back-up electricity supply at these times for some or all of your appliances. You will need a system designed and set up so it can ‘island’ itself and supply electricity independently of the grid. A few solar-only systems can island but if you want the back-up supply overnight and in cloudy weather you will need a battery. Learn more about batteries.

Make sure your solar retailer or installer is experienced at designing back-up systems and discuss your needs with them.

A battery for other reasons

A battery will store the energy generated by your solar system so you can use it when the sun is not shining.

This can increase your bill savings and make you more energy self-sufficient. However, a battery will increase the upfront cost of the system and take longer to pay for itself in savings. Read more about batteries.

Get an estimate of the cost and benefits of including a battery in your system with SunSPOT.

Grid-connected or off-grid

Most rooftop solar systems in Australia, even those with a battery, are grid-connected systems. This is the most cost-effective set-up for most properties. Off-grid solar systems (also called stand-alone power systems) are completely self-sufficient. They need a large battery and a control system and often have a back-up diesel or petrol generator to ensure a reliable supply during long periods of cloudy weather. Designing an off-grid system requires specific expertise and not all solar retailers and installers have this experience.

Although there are no electricity bills with an off-grid system, the upfront costs are much higher. In a remote area where connection to the electricity grid is unavailable, unreliable or very expensive, an off-grid system might be cheaper and more reliable than mains electricity. However, for most households and businesses it makes sense to keep a grid connection.

System monitoring

All solar systems have some kind of monitoring system showing basic information such as the operating mode and daily electricity generation, often displayed on a panel on the inverter.

You can add more detailed monitoring, including measuring your electricity usage and generation, in an easy-to-use app.

This can make it easier to detect system faults and manage your electricity use to make the best use of your solar.

Read more about monitoring.

Understand your current and future electricity use

The more electricity you use, the bigger the solar system you need. The financial benefits of solar also depend on when you use electricity.

You can find out about your electricity use from smart meter data (if you have a smart meter) or from your bills.

You should also consider how your electricity use might change in the future.

Talk to your solar retailer or installer about your current and future electricity needs to make sure you get the right size solar system for your property. Share your meter data and electricity bills with them to get an accurate assessment of your needs. 

Read more about how to size your solar system.

Know your roof

The design of your solar system will depend on the size and shape of your roof and how much sunlight it receives.

Roof direction

Solar panels can be installed on roof areas that face north, east, west or, in some cases, south.

Panels on north-facing roofs usually receive the most sunlight over the day and so generate the most electricity. Panels facing east will generate earlier in the morning while those facing west generate later in the afternoon.

If you use a lot of electricity early or late in the day, it can be a good idea to install 2 or more groups of panels facing different directions.

Panels on south-facing roofs will generate less electricity, particularly if the roof has a steep slope, and may not be cost-effective.

You can discuss the options for your roof with your solar retailer or installer. Combining different roof areas will affect how they design the system and the type of inverter.

Roof slope

On sloped roofs, solar panels are usually mounted flush or parallel to the roof.

On flat or lightly sloping roof areas, solar panels may be rack-mounted (installed on tilt-frames) to face them towards the sun. This can mean each panel generates more electricity, but there will be space between each row of panels (so the rows don’t shade each other) which may reduce the number of panels that fit on the roof. Rack mounting also adds to the cost.

Tilt frames can also be used on sloped roofs, but this is less common. For example, if the only available roof area faces south, it may be possible to use rack mounting to face panels north.

Shading

Solar panels generate less electricity if they are shaded by trees, buildings or other obstructions.

The amount of shading depends on the height and position of the shading object, the time of day and the season.

A little shading is not necessarily a problem, but if the panels are shaded for long periods they will generate less electricity and the system may not be cost-effective.

If there is shading on your roof, talk to your solar retailer or installer about designing a system that takes the shading into account.

You should also consider growth of trees or planned developments that might cause shading in the future.

SunSPOT

You can assess the slope and shading of your roof and estimate how much electricity can be generated on different parts of your roof with SunSPOT.

Solar panel orientation

Solar panels are most often installed in portrait orientation. This is usually quicker and cheaper because of the way mounting systems are designed. However, if your roof is short of space, it may be possible to install a bigger system with more panels by arranging them in landscape orientation.

A photo of two houses with an example of portrait and landscape orientation solar panels.

Solar panels in portrait orientation(left) and landscape orientation (right). Photo credit RJ Egan / APVI.

Roof type and condition

The type of roof will affect how your solar panels are installed. It is generally easier to attach solar panels to a corrugated steel roof than to a tiled roof.

Very steep roofs or double-storey roofs are harder to access and may increase the cost of the installation.

For some flat roofs, care needs to be taken to make sure the waterproof membrane is not damaged during installation. Some tilt frames can be secured using heavy weights (ballast) to avoid the need for fixings to penetrate the roof.

If your roof is likely to need repair or replacement in the next few years, this should be carried out before solar panels are installed.

Local regulations

The design of your rooftop solar system will need to comply with certain rules and regulations. Your local solar retailer or installer should be able to design a compliant system for you.

Network limits

Local distribution network service providers, the companies that own and operate the network infrastructure, poles and wires, set limits on the size of solar systems that can be connected to the grid and/or the amount of electricity that can be exported to the grid from rooftop solar.

Read more about network limits.

Local planning rules

Most rooftop solar can be installed without getting planning approval from the local, state or territory government.

But there may be restrictions on the size of solar installations, or how they are installed. If your property is in a heritage-listed area, there may be rules about where on the roof you can install solar, such as in a location not visible from the street. In this case, you may need to make a development application.

Your solar retailer or installer should be familiar with the planning rules.

Upgrading your existing rooftop solar system

You can add a battery to an existing solar system.

It is possible to add panels to an existing system in some cases, as long as there is space on your roof.

Depending on how the existing system has been designed and configured, new panels may need to be the same make and model as those currently installed in order to connect them to the same inverter. However, you may be able to install different panels along with a new inverter.

Contact your existing installer or another accredited installer to find out what is possible with your system.

If you do have old panels removed, find out about recycling.