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Buying solar - where do you start?

Over 1.5 million of Australians now live under solar rooftops. Household solar systems vary in their capacity and the number of solar panels that they use. So how do you figure out how many solar panels do you need for your home?

Solar basics: Panel number vs system capacity

Every solar photovoltaic (PV) system has a certain number of panels, but system size is not usually discussed in terms of the number of panels used. This is because not all solar panels are created equal: some will produce more energy than others.

The amount of energy that a panel can produce in a given location is a function of both panel size (i.e. the square meter area of the panel) and its efficiency (i.e. how effectively can it convert sunlight into usable energy). Combined, these two factors equate to a panel’s ‘capacity’, which is usually described in kilowatts (often written as kW).

Panels from about five years ago tended to be both smaller in size and less efficient than modern-day panels. Similarly, the capacity of solar PV systems from this period also tended to be on the small side by today’s standards, at around 1.5 – 2 kW as opposed to 3 – 5 kW. An older 2 kW system, for example, usually contained more panels (around 10 – 12) than a modern 2 kW system (around 8-10.)

The table below gives some examples of how solar systems of the same capacity could contain a different number of panels. (N.b. 1 kW equals 1000 watts, W.)

System capacity Number of panels (at 200 W per panel) Number of panels (at 250 W per panel)
2 kW 10 8
5 kW 25 20
10 kW 50 40

 

This shows that it’s more meaningful to talk about solar power in terms of capacity instead of the number of panels. A capacity figure will immediately give you an idea about the system’s energy generation potential, while the panel count won’t.

In fact, if you’re shopping around for solar, for this reason you’ll almost always see systems marketed in terms of their kilowatt capacity, and not the number of panels.

 number of panels against capacity

You’ll need to look at the capacity of the system rather than the number of panels.

What capacity solar system is right for your home?

The right amount of capacity your home depends on a range of factors. These include:

  • The amount of energy you consume during the daylight hours. For new solar systems (vs older systems on legacy feed-in tariffs), it makes the most financial sense to use the solar energy directly, while the sun is shining.

    Every unit of solar energy that you use directly is one less unit that you need to purchase from the grid. (Sending solar into the grid will earn you only small credits on your bill.) A useful analogy is growing some vegetables in your back yard instead of buying them all from the grocery store.

  • Your roof size. Provided you’ve got some daytime electricity usage, you’ll want a solar system that is large enough to meet your daytime needs.

    The main physical limitation on solar system size is the amount of unshaded roof space that you have access to, as shading from nearby trees or other objects on the roof can significantly limit your system’s energy production.

    In Australia, it’s also preferential to have your panels facing north, although east and west orientations may be suitable where north isn’t an option.

  • Whether you have batteries – or plan to get them. Directly consuming your solar energy is the best way to save money with solar panels, but they don’t generate power when the sun isn’t shining.

    If your solar system does produce more energy than you can consume during the day, batteries can help you to save the excess for later use. In fact, if you would like to maximise your independence from the grid by getting batteries, it probably makes sense to install a larger solar system than you would otherwise.

  • Your budget. Solar is more affordable than it’s ever been, but it’s not free, so your choice of sizes will also be limited by your budget.

    Even with budgetary constraints, however, it might be possible to arrange for a financing plan – be sure to check with a range of installers.


Without insights into your daily energy usage patterns, it’s hard to know in precise terms how effective a solar system will be at helping you save money on your bills, or what size system would be optimal for your home.

Over 1.5 million Australian homes have made the switch to solar, and most of them have done so without the data to help them make a well-informed decision. As a result, these homes may have systems that are either too large, too small or otherwise not living up to their full potential.

This is where carbonTRACK can help. Our units can be installed before you get solar (or batteries) to help you decide on a system that is best suited to your needs. In fact, our platform can even help you find ways to save energy and money before you go solar and effectively use your solar energy once your system is installed.

carbonTRACK can help you decide on the right solar system size – based on real data from your home. Find out more.