What Size Solar System Do I Need?

The size of your solar power system, and therefore the number of solar panels you need, should be informed by your electricity usage patterns and what you want to achieve.

Solar system sizes are measured in kilowatts and, depending on where you are and which direction your roof faces, each kilowatt of your solar panel system will produce between 3 and 5 kWh of clean, renewable energy per day. Typically, around 3 to 4 solar panels are needed to make up 1 kilowatt.

When it comes to buying your new solar system, don’t make the mistake of thinking ‘one size fits all’.


  • Your daily energy usage

The number of solar panels you might need should be informed by your current energy usage patterns and what you want to achieve. The best way to discover your current energy usage patterns is by reviewing your electricity bills. Collect your past year’s worth of electricity bills and look for your “average daily energy use” figure on each of them – it will typically be shown on the first or second page of the bill, and in kilowatt-hours or “kWh”. Note this number down for each bill you have, and then take an average of all of those numbers. The final number you arrive at will be your typical energy use over a 24 hour period, including both day and night-time hours.

Once you have this figure, load it into our simple solar calculator along with a little more information about you and your goals, and in seconds you’ll be able to see how many solar panels you might need.

  • Sunshine hours

Solar panels need sunlight to function – it’s an obvious rule. But what buyers often don’t realise is that their home’s exposure to sunlight, or how many sunshine hours they get, can have a direct impact on the number of solar panels they will need. The amount of sunlight your home receives change based on your location in Australia and the time of year. The decrease in sunshine hours during winter is due to shorter, cloudier days.

Of the Australian capital cities, Perth has the highest amount of average sunshine hours with Adelaide not far behind, and Melbourne has the least. This means that a household in Melbourne may need a larger sized system to make up the same amount of energy as a household in Adelaide or Perth, simply because of the sunlight they receive.

Match your solar panel placement with the time of day that you use the most energy.

The other thing to consider is how many of those sunlight hours can reach your solar panels, and the time of day that they will be exposed to sunlight. For example, a house with some shading on the roof might need more solar panels than a house with no shading, to make up for the panels receiving less sunlight. Or for a house that uses most of their energy during the morning, it might make more sense to put the solar panels on an east-facing roof space to capture the morning sun and generate free electricity when you need it most.

  • Your energy goals

The size of the solar energy system you need will also depend on how much you’re aiming to save on your future electricity bills. Do you want to just cover your daytime energy needs, or do you want to add a battery to make yourself almost completely self-sufficient? Have a clear goal in mind about how much of your energy requirements you’d like to have generated by your new solar energy system and share this goal with your solar energy system designer.

Your energy goals will directly influence the size of the system you need, the number of solar panels required, and the way it’s designed for future expansion.

Even if you select a smaller system that won’t supply 100% of your electricity needs, your new investment will still help to bring your electricity costs down almost immediately, and could set you up for an easy addition of a battery in the future.

If you do choose to start with a small system, ensure that your supplier has designed the system with expansion or modification in mind; you might want to expand your system size or add battery storage in the future if your circumstances change.

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