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If you’ve decided that solar energy is right for your home, your next step is working out how to size your solar PV system.

While there are many solar panel system size calculators available online, there are lots of different factors and considerations to take into account. We’ve put together this simple guide to help you figure out the right size rooftop solar PV system for your home.


“What size solar PV system do I need for my house?”

One of the first things to consider that will help you decide on your solar system size is determining how and when you use electricity in your household. 

Your daily usage will depend on a range of factors including the number of people living in your household, the types of appliances you use and how often you use these appliances.

For details of your daily electricity usage, take a look at your last electricity bill or use the data available in My Account. If you have a smart meter, you can use My Account to see when you use your electricity throughout the day in 30-minute intervals to help you to work out your daily electricity usage habits. 

The best use of your rooftop solar is to use up the solar energy your system generates during the day, so your daily usage patterns can tell you a lot about the size of system which might work best. If you discover that you use most of your electricity at night, you may find that investing in a solar PV system may not be the best choice for you. However if you still want to go solar, you might want to consider investing in battery storage or shifting some of your electricity usage to the middle of the day to make the most of your solar energy.


Roof space, size and design

Investing in a solar PV system is a popular way to embrace renewable energy – but it’s really important to have the right size to suit your energy needs and your roof space.

The size, orientation and layout of your roof space will influence what size system you can install. As a general rule, most solar panel sizes measure 1.7m by 1m each. For a 6kW solar PV system, you would need about 20 panels. The panels will need to physically fit on your roof space without any vents, antennas or chimneys in the way. 

The time of day you use most of your electricity is also something to consider when looking at the size and position of your solar PV system. Here in WA, north-facing solar panels are generally the most effective, as these solar panels will catch the most direct rays from the sun during the hottest parts of the day.

Depending on your roof space, you could have solar panels facing due east (to catch the morning sun) or due west (for the hot afternoon sun) – but north is generally the best position if possible. A well-designed solar system should also match your household’s electricity usage patterns. For example:

  • East-facing roof space

    If the morning is your busiest time of the day (for example, you’re getting the kids ready for school, doing the washing and ironing, running a dishwasher load) it’s best to install panels on the eastern roof.
  • West-facing roof space 

    If the afternoon is your peak energy usage time (everyone is home from work and school, the TV is on, as well as the computer and the air conditioner), the best orientation for your home could be west.
  • North-facing roof space

    If you use the most energy from mid-morning to the afternoon (which might suit stay-at-home parents, retirees or those working from home) installing panels on the north-facing roof space could give you the best return on your investment.
  • Whole roof

    If your energy usage is spread evenly throughout the day, purchasing a solar PV system size of between 5-6.6kW could give you the ability to spread your panels across your roof.

If you haven’t got the right amount of roof space you require for the solar system size you’d like, consider looking for panels that have higher efficiency ratings. They can take up less space while producing the same amount (or sometimes more) solar electricity. By choosing a higher efficiency panel, you can generate more solar electricity with less panels.

Here are some other things to consider when thinking about the size and placement of your solar PV system:

  • Shading

    If your roof is shaded by trees, taller buildings, or any other structure, this could have a big impact on how much solar electricity your system is able to generate.
  • Roof angle

    A completely flat roof is not ideal for solar panels but solar installers may recommend tilt frames to angle the panels for maximum sun exposure. Ideally, solar panels on a roof angled at between 15 and 35 degrees have the best chance of catching the most sunshine.
  • Roof vents, whirlybirds, and skylights

    Work with your solar installer to make sure your solar panels have been planned around obstacles like these.


Your future electricity usage 

The solar PV system size you need now might not be the same size you need in a few years. For example, if you’re considering installing a pool or air-conditioner, planning to buy an electric vehicle, starting to work from home or welcoming a new member of the family, then your daily usage is likely to increase over time. It could be easier and more cost-effective to plan ahead with a larger size solar PV system from the beginning, rather than try to add to it later.

On the other hand, if your children are leaving home or if you choose to invest in more energy efficient appliances, then you could find that that your daily usage will stay the same, or you might even find ways to reduce your electricity usage in future. 

Always consider your future electricity requirements to work out the best choice for your circumstances.


“What size solar battery do I need?”

While the high investment cost of battery storage solutions are a barrier for many, they may become more affordable in the coming years, so this may be something to factor in when considering your future energy requirements.

If you decide to go all in on solar energy and invest in battery storage, you’ll need to factor this into your solar system size decisions too.

For example, you might need a 5kW system to suit your electricity usage today, but if you decided to invest in battery storage later, you’d need a system large enough to generate enough energy to power your home and charge your battery. 


Consider your budget for solar

Buying a rooftop solar PV system is a significant investment in your home. You need a reputable, accredited solar supplier to recommend a solution which suits your home and the way you use electricity, while also keeping your budget in mind.

Whatever budget you’re working with, watch out for dodgy sales tactics and warranty conditions to ensure you are getting the best value overall.


A bigger solar system size isn’t always the best option

A common solar energy myth is that more solar panels automatically equates to more savings on your electricity bills. This simply isn’t the case. 

You may find that many solar installers and retailers will try to convince you that installing the largest possible system you can fit on your roof is the best solution. They might try to sell you on the idea that the more solar energy you can generate, the better. 

This could be better for them in terms of making money, however, investing in a larger solar PV system will mean a larger up-front cost for you, and it could generate more solar energy than you use which means it takes longer for your investment to pay off. 

The greatest financial benefit from having a solar PV system comes from when you use up the solar electricity generated from your system. The more solar electricity generated from your system that you actually use in your home, the more you can offset the electricity you would otherwise need to buy from the electricity grid. 

With this in mind, the way that you use solar energy is actually more important than the solar PV system size.  Generally, most solar system sizes will pay off within 3 – 5 years if you can shift your electricity usage to consume all or most of the solar electricity your system generates. 


As with any investment, long-term value doesn’t always mean the cheapest price upfront. It’s important to choose a quality solar system, sized to suit the way you use electricity at home.  Find out more about investing in a solar PV system and learn why you shouldn’t buy cheap solar