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How Big of A Solar System Do I Need at Home?

How big of a solar system do i need

How big of a solar system do I need at home? 

Should I spend everything I’ve got and create the biggest system I can, right away? Or should I start small and add more panels later on? These are important questions to ask when you’re planning on purchasing a solar panel system.

Understanding the size of the ideal solar panel system for your home is essential to make the most of the benefits on offer. This is the same for every system, whether you’re motivated by environmental concerns, financial savings, or energy independence. 

At the end of the day, there is no single, clear-cut answer to this question. That’s why in this article, we will delve into the key factors that influence the size of the ideal solar system and how to calculate the perfect number of panels for your home.

How Big of A Solar System Do I Need?

Before we jump into the sizing of a solar system, let’s talk about the basic unit of measurement first – kW. kW, or kilowatts, is a base unit used in the routine measurement of electrical energy. A kW equals a thousand Watts. So a 6.6kW system means a system that produces 6,600 watts (or more) of power a day.

The average electricity usage in Australia varies from one city to another. Here’s a glimpse of the average power use in capital cities based on household size.

Household sizeSydney (kWh)Brisbane (kWh)Adelaide (kWh)Melbourne (kWh)Hobart (kWh)

In Australia, the most typically installed solar panel system for households spans from 5kW to 7kW, with 6.6kW being the most popular. At this range, the system can usually generate enough energy to power the house while also lowering your electricity bills enough to provide you with a quick ROI. However, a larger household may well require a larger system.

You can always choose to install a larger system for financial reasons. The more electricity you produce, the less reliant you will be on the grid. This means larger savings in your electricity bills, particularly if you install a solar battery and feed excess power back into the grid.

There’s no one-size-fits-all answer for your solar system – everyone has their own budget, roof space, and electricity requirements, among many other factors.

Factors to consider before sizing your solar system

There are three key factors you need to consider before sizing up the perfect solar system. 

These factors include:

Physical space

The space available on your roof is a defining factor when deciding how big of a solar system you need at home. Before deciding on the size of your solar system, measure how many panels you can fit on your roof. If you’re unsure about the process, you can ask your solar installer to do a site assessment to determine the number.

Electricity requirements

A well-sized system is one that produces enough energy, and closely matches the power usage of your house. Your past energy bills provide a great way to estimate expected usage and calculate the ideal solar system size for your home.


Sometimes, budget can be a limiting factor when it comes to installing solar panels. However, these systems are becoming more and more affordable. The government also offers incentives and rebates to those who are eligible, lowering the upfront cost of installing solar at home.

How do I calculate the size of my solar system?

The formula to calculate the size of a solar system in terms of output is:

daily electricity consumption (kWh) / daily sunlight hours (h) = the size of a solar system (kW)

With that in mind, here’s a step-by-step process for determining the size of your solar system:

Step 1: Calculate your daily power consumption

You can get information on your power consumption from your most recent electricity bill. 

If you’re still using a traditional metering system, you can calculate it by adding up the total amount of electricity you used during the last 4 quarters (a year) and dividing it by 365.

It’s even easier if you’re using a solar smart meter since you can get the exact number directly from your electricity bill or your online account.

For example:

After adding up your electricity consumption for the last four quarters, you get a total of 5,475kWh. Divide that by 365 days in the year, and you’ll get a daily electricity consumption of 15kWh.

Step 2: Estimate the average of peak sun hours in your area

Peak sun hours are not the same as “hours of sunlight,” which are the hours between sunrise and dusk. A peak sun hour is defined as an hour throughout the day when the average intensity of sunlight is 1000 watts/metre².

Peak sun hours differ from one area to another. To determine the average peak sun hours in your area, you can search for results online. Alternatively, you can get a general overview in the table below.

City, StateAverage Daily Peak Sun Hours
Darwin, Northern Territory6.2
Perth, Western Australia5.5
Mildura, Victoria5.5
Brisbane, Queensland5.1
Sydney, New South Wales4.5
Melbourne, Victoria4.1
Adelaide, South Australia4.8
Hobart, Tasmania3.8

Step 3: Calculate the size of your solar system

Once steps one and two are done, you can calculate the size of your solar system by dividing your daily electricity consumption by the number of peak sun hours in your area.

For instance, in one of our service areas at Mildura, Victoria, we get (more or less) 5.5 peak sun hours daily. With a daily electricity consumption of 38.5 kWh, a rough estimation for the perfect solar system size would be:

38.5 kWh / 5.5 hours = 7 kW solar system.

Step 4: Account for inefficiencies (Optional)

Like other electronic devices, solar panels will also experience degradation over time, in terms of performance. This annual degradation is outlined in the solar panel specification sheet and will usually vary from 0.25% to 0.5% per year.

For instance, say your solar panels are rated 400W with a performance warranty of 30 years and an annual degradation of 0.50% per year. That means, by the end of their life cycles, those panels would only output 85% of their initial performance or 340W.

To compensate for the loss in performance, you can offset the size of your solar system by the amount of performance degradation. With that in mind, the size of the solar system for a 7kW system will be:

1.0 + 0.15 (performance degradation) * 7kW = 8kW system.

Step 5: Determine how many solar panels you need at home

It is easier to answer how many panels you will require once you have determined the size of your solar system. First, choose your solar panels. There are many options to choose from. But if you’re unsure, don’t shy away from considering expert help from Sungain Solar, for quality recommendations.

Let’s say for your 8kW solar system, you pick SunPower 350W MAXEON 2 solar panels. All you have to do is divide 8kW (8,000W) by 350W and the result is 23 solar panels. For more detailed information about solar panel sizes in Australia, you can check out this article.

Solar supply and installation

The numbers may be a little confusing, but we’re here to help. At Sungain Solar, we’re experts in supplying and installing solar panels for homes all over Australia. We conduct expert assessments to determine how many solar panels are required for your home – and we can certainly help you answer the question ‘how big of a solar system do I need at home?’.

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