Getting solar panels installed is an exciting time for people living in Australia. With so much natural sunlight, we can start to think about all the savings we’ll have by harnessing it. But how do you choose the right size solar panel for your home?
The most important part about choosing a solar panel system is ensuring it covers your present and future energy needs. Using electricity bills, you can find out how much energy your home uses, and speaking to a solar installer will help you find out what size solar system will support your home as it expands.
Choosing the size of solar panels and inverters is not a quick and easy choice to be made on a whim. You need to know that your investment will work properly for decades. In this article, we’ll cover everything you need to know about solar panel sizes, wattage and how to get the most out of your system. Let’s get started.
Table of Contents
How is Solar PV System Size Measured?
Solar panel size is measured in two different ways; the solar panel’s generational capacity, which is measured in either Watts (W) or kilowatts (kW), and its output, which is measured in kilowatt-hours (kWh).
It is important to remember that although both measurements are very much related, with one affecting the other, they are in no way interchangeable. For instance, a 4kW solar panel installed at your home does not necessarily mean that the panel is only generating 4kWh of energy every day. It only represents the size of the generation system inside your solar panel.
Although the solar panel’s generational capacity serves as a baseline to determine the output of your system, it is important to note that the output will still vary depending on several factors. But generally, you can expect a 1kW to generate around 4kWh of energy daily. With that in mind, a 4kW solar PV system will be able to generate around 16kWh of power per day, assuming that it receives the optimal amount of sunlight and in perfect weather conditions.
What Are the Different Sizes of Solar PV Systems?
The most widely used solar PV system sizes range from 1.5kW to 10kW, with solar systems that sometimes have up to thirty individual panels. These are usually more than enough to offset the energy needs of small to large families.
Below is a table showing how many solar panels are in solar systems of different sizes:
|System Size (Generational Capacity)||No. of Panels|
Keep in mind that a 1.5kW solar PV system will not always have 5 solar panels, since, despite panels having a standard physical sizing, manufacturers have the discretion to decide how much generational capacity each panel has. As such, one solar panel can have a capacity of anywhere between 250 to 340 watts.
What Is the Output of a Solar Panel System?
The output of solar panel systems differs even among those with the same generational capacities. For instance, a 1kW system will, on average, produce anywhere between 3.5kWh to 5kWh of energy. Alternatively, a 1.5kW system will produce approximately 5.25kWh to 7.5kWh of energy daily.
This table indicates the average solar panel kW production per state in Australia:
|City||Solar PV System Size (Generational Capacity) and Output|
The generational capacity is distinctly different from the output, and the energy output per day is never absolute. You can see from the table above that the area or environment greatly affects the output of solar panels. This means how much solar panel efficiency you can squeeze out of your system is affected by factors outside your control.
Residences located in areas that receive a lot of sunlight and warm weather, such as Alice Springs, Perth, and Darwin, will be able to take maximum advantage of their solar PV systems. While those in Hobart and Melbourne will produce much less energy with the same solar panel capacity.
What Is the Output of a Standard Solar Panel?
The output of a standard-sized solar panel is not fixed since manufacturers can set a panel’s generational capacity without changing its size and will differ, usually within the range of 250 to 340 watts per panel.
In addition, numerous factors affect the energy generation of the panels, ultimately changing the output. This means that despite all residential solar panels having the same physical dimensions, even among the same capacity panels, the output will still differ due to other factors.
You may, however, try to calculate the expected output of your solar panels by multiplying the solar panel’s power rating (generational capacity) by the number of sunlight hours in your area. Although the formula is basic and will not give you exact numbers, it will serve as a benchmark to guide your purchasing decision.
What Affects Solar PV System Output?
Panel size is the biggest factor that determines solar PV system output. However, other factors affect this, including the area, environment, and weather, among others.
Listed below are some of the main factors that affect solar panel output:
- Orientation – The overall orientation of your solar panels, which includes the angle and the tilt, is one of the largest factors that affect solar system output
- Usable daylight – How many daylight hours there are in the area you are located is directly tied to how much energy your system will produce
- Nearby obstructions – The surrounding environment, particularly obstructions to sunlight that shades over your panel (such as trees)
- Light intensity – The sunlight’s intensity in your area has an impact on the amount of energy your system can produce
- Local Climate – The ratio of sunny to cloudy days in your area and how much direct sun your panels can get is another major factor affecting solar panel efficiency
What Sized Solar PV System Do I Need?
The solar system size you need will depend on how much energy your household consumes on a weekly basis and how much your family is expected to grow in the next decade. A slightly larger system now can futureproof a rise in electric vehicles or additions to your family unit.
While identifying the right system size, there are generally two ‘schools of thought’. One is to simply cover the entirety of your roof with solar panels. This method will not always guarantee a quick return on your investment but is faster and simpler.
The other is to do some calculations and consultations with your solar installer to determine the size which will provide enough energy to ensure a positive ROI. This takes longer but is worth it in the long run.
For the former, remember that full-on ‘brute-forcing’ your roof into accommodating as many solar panels as possible isn’t also safe without consultations with your solar installer. Solar panels are not light, and your roof will have to be assessed to determine how much weight it can support. Having more panels also does not necessarily mean higher output since generational capacities differ between model and make, and factors such as environment and weather also play a role.
As such, we have listed the general considerations to be made when deciding the solar PV system size for your needs below.
Household Electricity Usage
Correctly sizing your solar PV system isn’t really possible unless you know how much electricity is actually being used at your home or even the predicted energy use if you’re planning to expand your family. This can be done by checking your previous energy bill and looking at the consumption over the last quarter. From the previous bills, you’d be able to calculate your average daily usage since power consumption is measured and billed in kilowatt-hours (kWh). However, the bill will sometimes highlight a ‘cost per day’ or ‘daily usage’ amount at the front or the back, measured in kWh.
On average, Australian homes use anywhere between 15 to 20 kWh every day, which could be more depending on how many individuals are living in the household, and whether they use gas or electricity for cooking. It is also important to remember that energy usage varies by season, with household energy consumption usually peaking in winter.
Location & Hours of Daylight
Solar PV systems need consistent exposure to sunlight to maximise energy generation, so your location’s daylight hours will be a critical factor. This is where seasons also come into the picture, as winter will obviously yield the least energy. Other environmental factors such as shade and obstructions will also hinder your solar PV system’s energy generation.
This one is tricky, as you have to decide whether you want to maximise your ROI or your solar offset. Unfortunately, you cannot achieve both simultaneously, which also affects the size of the system you will be getting. Maximising your solar offset will always require a much larger solar PV system, which also means a much more expensive upfront cost. Consult your local solar installer to identify which among the two will suit you and your needs best.
This is another important consideration that can be easy to forget. Solar panels are by no means small and light, they take up considerable amounts of space and are relatively heavy. Not all roof types can also support the weight of solar panels. Different sized solar PV systems will have different numbers of solar panels, and even among same sized systems with different manufacturers, the number of solar panels may vary.
For instance, a 1kW system can either have three or four solar panels depending on each panel’s generational capacity. Since the solar installer will also have to consider the best orientation of the panels for maximum solar panel efficiency, it may take some time for them to configure the best positions for your solar panels. But the bottom line is that you cannot have a large solar PV system if you have a small or weak roof.
Of course, before you even begin to calculate the ROI, the solar offset, and other factors, you have to make sure that you can afford the solar PV system you’re eyeing. How much solar panels cost is mostly affected by their capacity, with larger capacity systems being more expensive, which holds true despite the decreasing cost of solar in recent years. Consult with your solar provider to find out how to maximise your solar PV system given your budget constraints.
Solar Battery Use
When choosing a solar PV system, you should decide whether you want to complement it with a solar battery. If you’re planning to go off-grid (meaning you will be completely reliant on your solar PV system for your electricity needs), you will need a solar battery to store your excess power. However, for the majority who won’t, this is just an optional addition to your system.
Remember that not all solar batteries are compatible with all solar PV systems, so you cannot just have your system installed and think about buying a battery later. If a solar battery is an idea you keep coming back to, consider purchasing a solar PV system from a manufacturer who also makes batteries or one compatible with most solar batteries available on the market.
Your household’s energy usage will not necessarily stay the same forever. An expanding family and other additions that consume more electricity should be considered. Among these are electric vehicles, new appliances, adding a pool pump, or future plans to switch to electric cooling and heating. Ultimately you would want to leave a little allowance so that your household’s growing energy needs will still be met in the future, it just depends on how much allowance you are willing to allocate.
DNSP Export Limits
The Distributed Network Service Provider (DNSP) sets limitations that may hinder you from maxing out or filling your roof with solar panels. Every state and territory has rules for DNSP, but there are limits for single-phase and three-phase homes. Export limitations will automatically lower solar production to ensure that only a maximum designated amount of power will be sent to the grid at any given time.
How Do I Calculate What Size Solar PV System I Need?
Calculating what size solar system you need is done by taking into account your existing energy usage and comparing that with solar systems currently available while taking into account how your need for energy as a household may grow in the future.
Before calculating the solar PV system size for your house, identify the primary purpose of your system. Among these are; generating enough solar energy to offset energy usage, achieving a goal percentage of solar energy use, selling excess energy back into the grid (taking the DNSP limitations into account), or charging solar batteries to serve as backup.
There are a couple of tools you can use to calculate the best solar PV system size for your needs and consumption. Among these are the Solar Panel Estimator V3 and Solar & Battery Calculator from SolarQuotes. By inputting values such as available roof space, budget, energy consumption, and even future energy plans, you can identify the right solar PV system size.
How Do I Calculate How Much Energy My Home Uses?
To calculate your home’s energy use, you need to have copies of your previous energy bills and add up and divide the kWh values accordingly.
The steps to calculate how much energy your home uses are:
Step 1, Under Energy Terminology: Identify the difference between kilowatt (kW) and kilowatt-hour (kWh), knowing the difference between these two often interchanged terms will help you understand how to accurately determine the solar PV system size you will need. The W in both terms represent ‘Watt’, a measure of power.
This means solar PV systems are represented by their peak power — a 1kW system will be able to produce 1kW of power on days with intense sunlight. On the other hand, kWh measures energy instead of power. This means a 1kW system that consistently produces 1kW of power for an entire hour (60 minutes) would have produced a kW of energy.
Step 2, Identify Your Current Energy Usage: Take your last energy bill and look at the usage. This is most likely a quarterly bill, if not, modify your calculations as needed. The top of the bill should show how many kWh were used by your house in the last four quarters (adding all four quarters will give you your year’s consumption).
Step 3, Calculate Your Energy Requirements: Divide your yearly consumption (in kWh) by 365 to come up with your daily energy consumption.
How Do I Calculate How Many Solar Panels I Need?
The number of solar panels you would need would largely depend on your solar PV system size — a larger system will require more solar panels.
This table represents a general idea of how many solar panels are needed per system size:
|System Size (Generational Capacity)||No. of Panels|
This table only serves as a guide. Since manufacturers have the option to determine an individual solar panel’s generational capacity (kW), the number of panels you would need would depend on the capacity of each solar panel your system will use.
If you use low-capacity solar panels, you would need more, and vice versa. Solar panels have a capacity of anywhere from 250 to 340 watts.
Is a Bigger Solar PV System Better?
Yes, several solar panel experts will advise you to get the largest possible solar PV system that can fit onto your roof instead of meticulously calculating based on your needs. This is because you can get more out of your money for installing 33% more panels than a solar inverter is rated for.
6.6kW solar PV system sizes are considered superior since they fit into a ‘sweet spot’ for how much solar panels can fit on an average Australian home’s roof while also considering DNSP limitations. However, just having an ‘oversized’ system does not mean that you will produce more power than what your inverter is rated for. Of course, actual performance and capacity depend on your brand of solar inverter.
Even if you consider decreasing feed-in tariffs and DNSP limitations, maxing out your roof with solar panels is a wise move for several reasons:
Peak Energy Seasons – Winter and Summer seasons generally get the highest electricity usage for households. However, solar power systems pump out a massive amount of energy in summer, which helps offset large electricity bills with ease. On the other hand, your winter energy generation could be less than half of your summer’s; this makes it very difficult to offset winter season bills unless you have a much larger solar PV system.
Future Proofing – With the government-backed move to clean and renewable energy (which includes solar energy), more and more homes will be having battery storage and electric cars, which larger solar PV systems can help with since they need an extremely large amount of solar energy generation to charge reliably. So having just enough solar energy generation for your home will eventually put you at a disadvantage
In addition to these factors, requesting a quote on a solar PV system with a larger generational capacity is just much more cost-effective because, like with most other things, buying the solar panels in larger quantities yields a lower per unit cost. This is felt much more significantly for solar PV systems since the solar rebate is paid per kW of panels and covers most of its hardware costs. This means that after considering everything, including logistics and labour, adding more kW just gets cheaper.
Is My Roof Big Enough for a Solar Panel System?
The only way to accurately determine this is to have a solar installer come to check and assess your roof, who will also quote you on possible system sizes and configurations.
However, a tool you can use to help give you an idea of what system size can fit onto your roof is the Solar Power Panel Estimator V3. Remember that there are limitations to how large of a PV system you can fit onto your roof, depending on your DNSP.
How Much Electricity Does the Average Home Use in Australia?
Although electricity usage vastly differs between states and territories, as well as season and climate, the average Australian household consumes about 15 to 20kWh per day.
Autumn and Winter almost always require higher energy usage due to the widespread use of heating systems. On the other hand, depending on the state, either Summer or Spring sees the lowest energy usage for homes in Australia.
Are Bigger Solar Panels Better?
Bigger solar panels are generally better because they will always have a higher ratio of solar cells compared to smaller units. Larger panels also mean fewer solar panels for similar sized systems, which means fewer electrical connections, which should minimise damage, complications and repair costs.
However, larger panels are not without issues. Due to their size and weight, they may restrict your system design since they won’t always fit on every type of roof. Their large size also makes them a little more dangerous to install on a roof.
This article is published in good faith and for general informational purposes only. JFK Electrical does not make any warranties about the ongoing completeness and reliability of this information. Always seek personalised advice on solar energy to ensure any recommendations suit your property and scenario.
John Lyons, the owner of JFK Electrical Solar & Air, started his career in the electrical industry in 1997. With years of experience gained in the industry across multiple continents, he relocated to Australia and decided to specialise in solar and air conditioning. After deciding he wanted to be closer to his family, John began his own local electrical business in Mandurah, using his extensive knowledge and training in the industry. At JFK, John’s number one goal is to provide tailored solutions to his customers. And thanks to his experience and commitment to his customers, JFK Electrical is now one of the most trusted local businesses in Mandurah for solar and electrical services.