Solar panel size calculator

How many panels you need depends on the size of the system you plan to install. A different number of panels can make up the same size system. For example, a 6.6kW system can be made up of anywhere between 13 - 15 panels. A system this size is typically large enough to power a small - medium size Australian home.

There is much to consider when sizing a solar system; we explain when to install a bigger system and, the importance of understanding your future energy needs.

Getting your system size right depends on six individual factors:

• 1. Your electricity consumption
• 2. When you use your electricity
• 3. Your location
• 4. Your available roof space
• 5. Installing a solar battery
• 6. Your future energy plans

This article will take you through how to use our Solar System Size Calculator. We’ll also explain everything you need to know when deciding how many solar panels will be enough to power your home, with or without the help of our calculator.

Solar panel wattage

The size of a solar panel system is measured in kilowatts (kW). Each solar panel has a rated capacity of how much power it can generate in ideal conditions, measured in watts (W) e.g. 475W. The rated capacity is often referred to as the solar panel size.

One kilowatt is equal to 1,000 Watts.

If a system is made up of 17 x 475W panels, then the total system size is 8.075kW - which is marketed as an 8kW system.

Solar panel size dimensions

It’s also important to understand the physical size dimensions of solar panels so that you can calculate how many panels you can fit onto your roof.

The typical household panel comes in the standard width and length dimensions of 1.70m x 1.00m (170cm x 100cm). The depth, or thickness, of solar panels varies with the manufacturer, but is typically between 30mm – 40mm.

Standard panel dimensions

Applying the 1.0m x 1.7m standard dimensions, every panel requires 1.7m2 of roof space. For the 17 x 475W panel 8kW system in our earlier example, you would need 28.9m² of roof space. The roof area required will change if the rated power output of the panel is different. For example, if the system is made up of 18 x 440W panels, you’ll need 30.6m2 of space on your roof.

Important note: Not all solar panels are exactly the same size. Some panels are slightly longer at 1.8m.

How much roof space do solar panels need?

As the panel wattage increases with technology, the roof area required for a system decreases. The table below shows the number of panels and roof area required for different system sizes:

Number of panels and roof area required per system size

Solar panel weight

As a guide, each domestic solar panel typically weighs between 20 – 25 kgs. Though the exact weight varies by manufacturer, as evidenced in the table of high-performing panels below:

Most household rooftops can withstand the weight of a solar panel system.

Sun exposure at your property

The first step is to calculate how much sunlight hits your rooftop where your solar panels will be positioned. Our calculator asks for your postcode, so that it can source the nearest weather station data to your location.

Once we have the data on sunlight hours, we then need to consider limiting factors that impact the electricity output of the solar panels on your roof, these include:

• Roof orientation
• Roof angle
• Shading or obstruction

Roof orientation

Solar panels will generate more power if you can install them on a roof that faces north. If your roof’s orientation is east or west, that’s ok too.

Roof angle

Solar panels are typically installed on the same angle of your roof, unless it is flat. If the angle of your roof is less than 10°, it will start to impact your system’s output.

Shading and obstruction

If your rooftop solar panels are shaded, or obstructed by another building, this will reduce their output.

Your electricity consumption

The next piece of information we need is how much electricity your house consumes on a daily basis. You can find this information on your electricity bills, or failing that, you can use this electricity usage calculator.

Electricity use is measured in kilowatt-hours (kWh). As a guide, the average Australian household uses approximately 15.31 kWh of electricity per day.

Daytime electricity use

You also need to estimate your electricity use during daylight hours. Knowing this, tells you how much electricity you will be able to self-consume once your solar system is up and running.

When you use electricity

When you use your electricity is important in determining the right system size.

Let's work through an example that considers daytime electricity use.

A house in Adelaide that consumes 18 kWh of electricity each day would need a 5kW solar system to generate enough energy to offset electricity consumption. However, if the household only consumes 40% (7.2 kWh) of its electricity during daylight hours, such a large system may not be necessary, unless it plans on installing a battery.

Without a battery, a 3kW system that generates on average 12.6 kWh of electricity per day would be sufficient and, would provide the most affordable solution. However, it leaves no room for future energy demand e.g. electric vehicles.

Your budget

Your budget is a factor. If you cannot afford, or do not want to buy a 5 or 6.6kW solar system, then we recommend selecting the most suitable size system you can afford.

Before you let budget constraints impact your system size, check to see if there are any additional solar panel rebates available in your state or local council zone.

If the upfront cost of solar is an issue, you may consider financing the purchase with a solar loan.

Your available roof space

How much roof space you have is really important in determining how many panels you need. If you cannot fit the system size that you want onto your roof, you’ll need to select a smaller installation or higher rated panels.

The greater the panel efficiency, the higher the power output of the panel. The higher the power output, the less panels you will need.

For example, A 6.6kW solar system might use 13 x 510W panels, or 15 x 440W panels.

Do you plan to buy a solar battery?

Consider whether you plan to add a solar battery to your solar system. If you do get a battery, you will need enough solar panels to directly power your appliances during the day and charge your battery, so that you can use that stored solar power at night.

The economics for adding a battery have improved considerably with the federal government solar battery rebate.

How a battery impacts system size

Let's use the example of a household in Brisbane to show how adding a battery increases the system size. For this example, we assume:

• Average daily electricity use = 25 kWh
• Average daily daylight hours use = 10 kWh
• Future electricity use is not increasing

A 6.6kW system is large enough to cover the daily electricity use, as it will produce an average of 28 kWh per day. The table below shows where that 28 kWh goes:

If the household didn't plan to get a solar battery, then they do not need as many panels. They would only need a system size large enough to comfortably power their 10 kWh of daylight electricity use. A 3kW system may generate enough energy to cover the electricity use.

However, it's wise to upsize the system where possible, it may be that a system size of 4.5kW provides the best solution.

Future energy plans

If you buy good quality solar panels, you can expect them to last well over 25 years. That’s why it’s important to consider your future energy plans, not just your consumption today.

More and more households are seeking to electrify their energy needs, so that they can be powered by renewable energy. Doing so, will likely increase the amount of electricity you use. So, it's worth considering if you are planning to:

• Buy an electric vehicle (EV)?
• Switch gas appliances over to electric?
• An extension to your house?
• Install a pool or add pool heating?

Even if you feel you are not likely to do any of the above in the near future, consider what type of car you will buy next. Will it be electric? If so, then it makes sense to add additional solar panels to charge the EV.

Your calculator results

Our system size calculator considers all of your inputs before displaying an appropriate size system.

Should I buy a bigger solar system?

If you have the roof space and the finances, it can make sense to buy a larger system size.

Some benefits of a larger size system include:

• Economies of scale
• Future electricity use
• Better value per kW
• Panels don't produce as much electricity in winter

Economies of scale

No matter what system size you choose, the labour time represents a significant portion of the overall cost. Once the initial installation tasks are complete, adding more panels doesn’t add that much extra labour.

In addition, larger inverters and extra panels often come at a comparatively lower cost.

Future electricity use

Selecting a larger system can insure you against a future increase in electricity demand due to: EVs, electrification or a home extension. excess energy you export back to the grid.

Better value per kW

When looking at the cost of solar panels, larger systems often have a lower price per kilowatt. So, if you choose a bigger system, you might get more power for your money.

Take for example the price in Sydney for 3kW and 5kW solar systems:

When looking at the system price in this example, you pay a $806 per kW to upgrade from 5kW to 8kW.

Panels don't produce as much electricity in winter

When sizing a solar system, you should consider how much electricity your solar panels will generate in winter months.

Solar production decreases in winter months due to lower sunlight hours. Exactly how much lower solar yields are depends on your location.

Let’s take a look at the effect reduced winter generation has on system sizes in Melbourne.

Electricity use:

Daily electricity = 18 kWh (Australian average)

Daylight use = 7.2 kWh (Assume 40%)

The output of a 5kW system:

Average daily output = 18 kWh

Winter daily output = 9.0 kWh

In this example, a 5kW system will produce enough electricity in winter to power the daylight usage of 7.2 kWh. A smaller system would not be able to generate enough electricity to power the household’s daylight energy use in winter.

Maximum system size limits

Depending on where you live, there may be limits that affect the maximum size of the system you can install. These limits are set by your electricity network provider and not your electricity retailer.

Solar export limits are put in place to restrict the amount of electricity you can export to the grid. Technically, the limit is placed on the inverter and not the system size. In some cases, export limits are as low 5kW.

Inverter sizing

The size of your inverter does not always need to match the size of your panel system. Often, an installer may pair your solar panels with a slightly smaller size inverter. The reason they do this is because the panels rarely operate at their rated power output capacity.

For example, it is possible to install a 6.6kW system with a 5kW inverter.

3-Phase power affords you a higher limit

If you have a 3 -Phase power connection, you typically have a higher export limit. Export limits are applied to each phase, so if there is a 5kW inverter limit, you can install a system with a 15kW 3-Phase inverter and effectively triple the system size allowed on a single phase connection.

This resource can help determine what size inverter you can install at your property.

Payback, savings and reducing emissions

Your goals for installing solar panels also impact the size and type of the system you install.

Consider savings and payback period

If your goals are purely financial, the cost, savings and payback are likely to influence your system size decision.

If this is the case, we recommend using our solar savings calculator. It lets you play around with different system sizes, using a toggle, to see the impact they have on the upfront cost, annual savings, payback period and your carbon emissions.

It also tells you how many panels you need based on that system size.

Offsetting home energy use

A goal for many solar owners is to offset their electricity use. With average electricity consumption around the 15.31 kWh / day level, typically a 5kW or 6.6kW system is large enough.

However, gas consumption is not included in the daily energy use figures. With the move away from gas towards household electrification and electric vehicles, electricity consumption is expected to rise significantly.

Rewiring Australia estimates that the average fully electrified household will use around 37kWh of electricity per day ¹. Powering all of this electricity will require a 10kW - 13kW solar panel system.

¹ Rewiring Australia electrified household energy use

Reducing your household emissions

If your goal is to reduce your household emissions as much as possible, then try and fill your roof with solar! Go for as large a system as is feasible.

Kilowatt (kW)

A kilowatt (kW) is a unit that measures how much power a solar system can produce. One kilowatt is equal to 1,000 Watts.

Kilowatt hours (kWh)

A kilowatt-hour (kWh) is unit that measures how much energy a solar system can produce per hour.

Solar system size

Solar system size is a measure of the power capacity of a solar panel system. To measure system size, you simply add up the wattages of all the solar panels in the system. A system comprising 16 500-watt solar panels has a system size of 8kW.

Wattage output

Wattage output is the amount of power a solar panel can produce in ideal conditions. It is measured in watts (W) and represents the system's capacity to generate energy.