What size solar system do I need?

Published: 13 March 2018

If you want to try and get your head around how big our solar system, as in where the earth enjoys its annual orbit, is—it has a diameter of approximately 287 billion kilometres. Like…way big!


The solar system you will need to power your washing machine and air conditioners is considerably smaller. It will, in all likelihood, fit neatly on the roof of your house. Marvellous! As more and more Australians begin their investigations into the benefits of running their homes using solar power, “What size solar system do I actually need?” is by and large the most frequent question fielded by solar retailers and installers.

Ultimately, it’s a numbers question. But luckily for us, the numbers are fairly easy numbers to digest, unlike the ridiculously large numbers required to measure outer space.

This article is all about helping you understand size in solar terms. After reading this article, accompanying links, and becoming familiar with a few simple terms, we’re confident you’ll be sufficiently enlightened and far more solar size savvy.

In fact, we think you’ll have a pretty accurate idea of the size of solar system you will need to purchase to power your home now and into the future.

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How to Use This Article

For many readers, some terms and language will sound completely alien—that’s to be expected. This is a relatively new technology in domestic terms, and much of the language hasn’t made it into daily conversation. Few of us use words like ‘kilowatts’ or ‘photovoltaics’ in a sentence.

Throughout the article, we’ll provide links to definitions and other key terms that will allow you to become a solar lingo legend. Used in context, this language will begin to garner meaning for you.

Follow the links and do your best to get your head around the definitions. They’re presented in a manner you and I can understand. You don’t need a science degree—we’re all about creating understanding. Solar is for the people.

Before you start, you’ll need a couple of things. A recent electricity bill, a pen, your thinking cap and a glass of something tasty. Oh, and make sure your husband is out in the garden, he’ll just make things more difficult.

So Where Do I Begin?

When you first venture into solar, you’ll find questions beget questions. We can hear you thinking from here. Do I need a 5kW system? What is 5kW anyway? How much power will a 1kW system give me? Our roof area is not so large, how many solar panels will we need? There are only two people living at our house, can we get a really small system and save money? All good questions.

The first option you have is to call a retailer or supplier, and rely completely on them for all the answers, information, calculation and advice.

A good retailer and installer is genuinely worth their weight in gold and can provide fabulous clarity and understanding.

A great option, however, is to have your own serviceable understanding of solar size. This way you have a better chance of sorting the players from the pros. We can’t recommend going in blind to start your negotiations with suppliers if it can be avoided.OK, Let’s Start

There is a number of variables that need to be reined in to determine what size solar system you will need.

The two critical factors are the amount of electricity you use throughout the daylight hours and whether you’ll be installing a battery to power the house at night.

1. How much power do I use?

This is where you will need your electricity bill. Yes, we know it hurts to look at it—this is the reason you’re going solar in the first place.

Your bill, however, is the key tool for determining just how much power you use.

OK, from here on we’ll assume you’ve just earned a B+ in understanding electricity bills and you have gone through yours. Brilliant.

The critical number on your bill is the number that states your annual electricity usage in kWh (kilowatt hours). Divide this number by 365 and you will have the figure for your daily electricity usage. Write this down.

A quick note about comparisons and relativities

It’s important to take care when thinking of electricity demands in terms of the number of people in the house. It is a consideration, yes, but it can be misleading.

Here’s an over the top example to illustrate a point.

Robert, your neighbour, lives alone. But Robert has an Olympic-size pool in the backyard which he heats, and it’s lit by halide lights the size of which can illuminate the Gabba. He also has ducted air-con running 24/7.

He’s just installed a Ferris Wheel for the grandkids the size of the London Eye. He now wants to set up a dodgem cars amusement ride for said grandkids, and a particle accelerator for his own scientific amusement.

You, on the other hand, have 5 people living in your house. The family BBQs every day for dinner, religiously, and it’s wood fired. There are no air conditioners—you use fans. The hot water is gas powered, there’s no pool and no garden lighting or clothes drier.

In fact, the whole family is now using candles to light the house in order to reduce your carbon footprint, and you’re still using your great grandfather’s icebox for refrigeration. What’s more, you’re happy with this and don’t plan to change your habits any time soon.

Clearly, Robert’s sole electricity demands far outweigh the demands of your 5-person household.

Obviously, we’ve used some fun exaggeration to bring home the message here. Looking at the solar installations of others can be useful for guide purposes, but you must understand the usage in your household to determine what size solar system you will need.

2. When do I use the most electricity?

Have a think about how you operate at home. Do you use the washing machine and drier during the day or in the evening? Do you run the air-con at night or during the day?

Generally speaking, most people use the bulk of their electricity in the mornings and early evenings. It’s also important to note, are you out during the bulk of the day? Kids at school, mum and dad at work? Or are you retired, spending much of your time in?

Make some notes about your daily habits, the habits that require electricity. Your installer will find this very handy when you get to the business end of determining what size solar system you will need.

3. Future plans

Your power bill provides a very accurate measure of the electricity you are using now and your demands in the past. But what about the future?

Make notes of your plans. Your retailer will find this information very important too. Do you intend to install a pool? How big? Will you heat it?

Will you get ducted air conditioning? Are you planning to have a large family? Will you renovate your kitchen and install bigger, more power-hungry appliances?

You can install a system sized to cope with your future demands right off the bat. Alternatively, you can fit up solar to meet current demands ensuring there are options for upgrading and upsizing in the future.

4. Solar calculators

With the proliferation of domestic solar power has come a wonderful selection of useful resources to help consumers.

Solar calculators are designed to give you a solid insight into your solar requirements. And all you need are a few readily available numbers.

Follow these links to an independent solar calculator.

This link will take you to a solar calculator that measures the amount of power you will need.

Note: This calculation requires you know the pitch or incline of your roof. The mathematically minded or spatially aware can hazard a pretty good guess.

For the rest of us, grab a protractor from your kid’s pencil case and hold it up to the roof line for an approximation.

You also need to know the orientation of your house. Are you facing north, south, east or west? If you’re not sure, take a look at a map of your street.

The map will show the orientation and you will be able to determine the direction your house is facing.

This link will take you to a solar calculator that suggests a solar system size for you.

It is important to note that the figures provided with these calculators are nominal. It is nigh on impossible to provide exact numbers as every situation will vary depending on several factors. Some of the Variables That Affect the Numbers

· Your location affects the productivity of solar panels. Some areas are sunnier than others. Most calculators take this into account.

· Shadowing over your roof will also affect panel efficiency. Calculators DO NOT take this into account.

· The pitch or incline of your roof also determines panel efficiency. Many calculators take this into account, but the numbers are determined by the accuracy of your measurement.

· The quality, type and capacity of solar panels are big variables. The panels you install will be determined largely by your budget.

· The available area of your roof will also play a significant role in determining the size of your solar system.

· The use of home battery power has impact on the system size you will need. Most solar calculators will ask if you intend to use battery power.

Just solar? Or will you be using a battery to power your home in the evenings?

Your solar array will only generate power during the daylight hours. It needs the sun. To maximise the value and savings from solar, home battery power is ideal.

With an appropriately sized solar system, excess electricity—that is, electricity not used running appliances during the day—is channelled to the home battery.

When the sun goes down, a fully charged battery takes over the electrical demands of your home. Yes, even though the sun has gone, you are still running on solar power. Brilliant.

It’s a given that if you wish to use battery power, you will need to generate excess electricity during the day. It is likely that a bigger solar system will be required to generate this excess.

How big is big? Putting size in perspective

Common domestic solar systems generally range from 1.5kW to 10kW. There are variations on this, but 1.5 to 10 and everywhere in between is pretty common in Australia.

The 1.5kW system

A typical 1.5kW system requires 6 panels, assuming 270-watt panels. The panels are approximate 1600mm X 1000mm. An array of 6 panels requires about 10 square meters of roof space. This system will generate on average (averaged across seasons and locations) 6.3kWh per day.

This is indeed a small system and will suit only minimal electricity demands. It’s unlikely a battery would be recommended for such a size system. It’s suitable for a small two-bedroom home with air-conditioning.

The 3kW system

A typical 3kW system is frequently chosen by many modestly sized, working families in Australia.

It accounts for standard electricity use, including things such as a standard size inground pool and a few air conditioners. A 3kW system will generate approximately 12.6-kWh per day.

You will require 12 panels at 270 watts per panel. The panel size is 1600mm X 1000mm and will require approximately 20 square meters of roof space.

The 10kW system

The 10-kW system will suit a very large family with heavy electricity demands. You may have a large in-ground pool demanding several pumps and you may have 4 to 5 bedrooms with ducted air conditioning and in-floor heating.

Typically, you have mum, dad, extended family, e.g. grandparents, 3 to 5 kids and a bunch of regular visitors.

A 10-kW system requires 37 solar panels and a roof space of about 64 square meters. You will likely be returning power to the grid or running the evening household demands on the battery. There is no doubt that this is an expensive array. A 10kW system will generate up to 42 kWh of electricity per day. That’s big.

To give you an idea, this array can power up to two ducted air-conditioning units, multiple pool pumps and in excess of 30 deep freezers. Yes, wow!

Have another look at the figures you have on your bill and the answers provided by the solar calculators. Compare them now to the “Putting Size in Perspective” section above.

By now, you should be getting a pretty strong indication as to what size solar system you need to power your household now and into the future—and of how big is big.

Of course, this process seems like a lot to go through. For many of us, these sorts of calculation tend to do our heads in, or at least make us nervous.

It’s a lot easier to digest, however, when we keep in mind that the move to solar is going to save us a heap of cash.

Over the longer term, it will amount to very significant savings. Better still, we can significantly reduce our carbon footprint.

For the majority of Australians, there’s a solar system sized to suit our needs perfectly. Now that you know the size you need, it’s time to take the next step, contact us today!

Next Steps…

Interested in solar? By clicking below you can use our smart solar calculator to find out just how much you could save with solar, what rebate you are eligible for, and the impact you will have on the environment.

Don’t wait until next quarter’s bloated bill, and get started today!

Click here to calculate your solar savings!

Join over 20,000 homeowners who have made the switch with Nectr, or the 1000+ positive reviewers who have been more than happy with their solar install.

Otherwise, you can always contact us on 1300 133 556, or email if you prefer at sales@instylesolar.com.au.

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