Solar system size: Calculate yours

Find your optimal system size

Selecting the right system size depends on:

  • Your budget
  • Available roof space
  • Electricity use
  • Future energy plans

Bigger is now better: Think 5kW+

It is now better to buy bigger due to the lower cost of solar panels, higher feed-in tariffs and the fast payback on additional kilowatts. If you can afford the upfront cost and have the roof space, we recommend selecting a system size of no less than 5kW; indeed, the new sweet spot of a 6,6kW system with a 5kW inverter is a good option.

The price of a 5kW system varies according to your location but expect to pay between $5,500 – $8,000 for a good, reliable unit and a quality installation.

Is the system cost or roof space an issue?

If you are not able to stomach the higher upfront cost, or you do not have the roof space, then you should size a system according to your electricity usage, in particular during daylight hours. Let’s delve into the calculations.

graphic showing a person wondering how many panels to buy
Calculate your system size

Your system size results

How many solar panels do I need?

The number of solar panels that you need depends on the system size that you select. However, you can have a different number of panels for the same size system. A 5kW solar system can be made up of 20 x 250W panels, or 15 x 333W panels, it all depends on the efficiency of the solar panels you select. The higher the efficiency, the less solar panels you will need.

graphic showing 15 - 20 panels needed for a 5kW solar system

Buy with confidence

Physical size of solar panels

A 5kW solar system may produce enough energy to power your home, but you may not have enough roof space for a system of that size. Solar panels for households typically come in the standard dimensions of 1.70m x 1.00m, that’s around 1.7m2 for every panel installed. However, the wattage output (W) of the panels will likely vary between 250W and 360W for a more efficient module.

As a guide, you’ll need 4 x 250W panels, or 3 x 330W for every 1kW of your solar system. If you’re considering a 5kW system, that’s between 15 and 20 solar panels that will require anywhere between 25.5 – 34m2 of roof space.

solar panel dimensions and roof area graphic

Why we recommend a larger system

We recommend selecting a larger system size than what you may necessarily need; so long as you can afford the upfront cost and have the roof space. Our primary reasons for this are:

  • Higher feed-in tariffs
  • Lower cost of larger systems
  • Faster payback: cost vs value of additional kWs
  • Future planning for storage or greater use

Higher feed-in tariffs

Higher feed-in tariffs have made the solar payback and savings equation more appealing. Where once it was desirable to select a system size that met your daily needs, now you can select a larger system and be better rewarded financially for the excess power that you export back to the grid.

Economies of scale of buying bigger

The key cost difference between a smaller system and a larger one is in the labour time it takes to install the unit. It does not take a solar installation team much longer to install a 5kW system than it does a 3kW system. You will need a larger inverter and more panels, but the additional cost of these added components is relatively cheaper.

Cost vs value of additional kWs

If we look at the cost of different sized solar panels, it’s clear that the larger the system, the cheaper the price per kilowatt (kW). We can explain this by comparing solar panel prices in Sydney for 3kW and 5kW solar systems:

  • 3kW system in Sydney $4,397
  • 5kW system in Sydney $5,866

The price you will pay per kilowatt:

  • 3kw system = $1,465
  • Additional 2kw = $734

Fast payback on additional kWs

The cost of increasing the size of the system to 5kW is only $734 per kW. If we assume that you receive a feed-in tariff of 11.1c for every kWh you export back to the grid, it will only take 4.5 years to pay back the extra 2kW; this is assuming that all of the additional solar power output is exported back to the grid. If you self-consume the power, it will pay back much faster. You can expect the panels to continue generating solar power for another 20 years.

System size if you cannot afford a larger unit

If you cannot afford, or do not want to buy a 5 or 6.6kW solar system, then you need to calculate the amount of electricity you consume during daylight hours and work back to find the right system size.

System size based on daylight electricity use

The average Australian household consumes 18kWh of electricity each day. If we use a house in Adelaide as an example, you would need a 5kW solar system to generate this amount of power. However, if the household only consumes 40% of its electricity during daylight hours, there is no point in installing such a large system. In this instance, a system that generates on average 7.2kW (40% x 18 kW) of electricity per day would be sufficient. Therefore, a 3kW system is likely to deliver the most affordable solution.

Consider lower winter output

Due to a shortage of sunshine hours in the winter months, the solar panel output is significantly less. Ideally, you want a solar power system to generate enough electricity to power your heating needs in the depths of winter. We look at the effect of winter generation on your system size decision using the example for a Melbourne property below:

Electricity use:

  • Daily electricity = 18kWh (Australian average)
  • Daylight use = 7.2kWh (Assume 40%)

The output of a 5kW system:

  • Average daily output = 18kWh
  • Winter daily output = 8.1kWh

In this example, a 5kW system will produce enough electricity in winter to power the daylight usage of 7.2kWh. A smaller system would not be able to generate enough electricity to power the household’s daylight energy use in the winter months, and this is another reason why selecting a bigger system size is the best way to go.

Considering adding a battery?

If you are planning on installing a panel and battery system, the system size equation can change. Your solar panels need to generate enough to directly power your appliances during the day and charge your battery. If you can afford a 6.6kW system and have the roof space, then you may not need to buy more solar panels to charge your battery. The size increase depends on how much battery storage you believe you need and, your solar expectations during winter months. Consider the example for a Brisbane property below:

Electricity use:

  • Daily electricity = 25kWh
  • Daylight use = 10kWh
  • Winter electricity 20kWh

A 6.6kW solar system in Brisbane would generate, on average, nearly 28kWh per day. Enough in theory to power the household’s electricity day and night, in this instance, 25kWh.

The output of a 6.6kW system in Brisbane:

  • Average daily output = 27.7kWh
  • Winter daily output = 18.9kWh

The winter output of the 6.6Kw system of 18.9kWh nearly generates enough to power the total daily electricity use, which includes charging the battery then drawing on that power at night. However, if the winter electricity demand was higher and more like the daily average of 25kWh, then the household should consider a system size of 8.5kW or more.

Future planning

When weighing up which system size to install, you should also consider your future electricity needs. We list some considerations below:

  • Do you plan to buy an electric vehicle?
  • Do you plan to switch to electric heating and cooling?
  • Are you planning to add a pool pump?

It’s more likely to be cost-effective to buy a larger system than you currently need, rather than add to the system at a later date. You may pay back the additional cost of the system even before you increase your electricity use.

GET 3 FREE
SOLAR QUOTES

Let us recommend 3 local, certified, solar installers to provide you with a free quote on your off grid system