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What Size Solar System Do I Need?

Solar power has never been so affordable with the government rebate still available and record-low prices on solar panels. In fact, it is now possible to get a top-quality solar system to pay for itself within 3-5 years, saving your households tens of thousands of dollars over the life of the system.
Tom Sedgwick
Updated at
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3 min

Roughly Sizing Up A Solar System

Roughly sizing up a solar system is easy; solar power can save you around $400 per kW per year, and a solar system will output around 4 times its size as a daily average.

For example, a 5kW system will output around 20 kWh a day and may save you up to around $500 every quarterly power bill. For many households, this rule of thumb is good enough to answer the question of ‘how much solar do I need?’

As solar power prices continue to fall and battery storage is now a realistic option for most households, we are now starting to size up nearly all of our solar systems to match your 24-hour usage rather than guessing how much solar you could use during the daytime.

Sizing Up A Solar System

The average size solar system we are now installing is around 8kW-10kW, or to basically fill the roof with panels where roof space is a limitation. The main reasons for this are:

  • Good quality solar systems are significantly cheaper than they were previously

  • Feed-in tariffs are now very healthy to the point where it makes good financial sense to over-size your solar to reduce your power bill. With an over-sized solar system, many of our customers are enjoying a credit on their power bill every quarter (as in they are getting paid money from their energy retailer instead of having to pay a power bill)

  • Government rebates are still in place, and the larger the system, the larger the rebate. The ACCC also keeps advising the government to get rid of the rebates as soon as they can, and there is certainly the chance that this could happen

  • Property prices are increasing at such a rate that it is becoming a no-brainer to use some equity to replace your power bills for the coming decades and add value to your home

  • Batteries have changed the market. Whether you buy one now or in the future it’s advisable to get your solar system installed now with the presumption that you will store excess solar power at some stage in the future in a battery. This means sizing up a solar system based on your 24-hour usage, and until you get the battery installed you will get paid a good feed-in tariff from your energy retailer

Graph showing return on investment in solar systems

How Many Solar Panels Do I Need

Once you know how much solar power you will need across an average day, you can then work out how many panels you will need to generate that amount of power. Most solar good panels are now rated 400W per panel, with highly-efficient panels being around 400W-420W. The solar panel size is around 1.7m by 1m.

Generally, high-efficiency modules are more expensive per panel, however, because you need fewer panels for the same output it is often recommended to choose a panel such.

As an example, if you decide to go with a 10kW solar system for your home, you could then choose to install 24 x 415W panels, rather than 29 x 350W panels.

It is recommended that you spend a bit of time on the phone so that we can discuss the various options and help you understand the value of the different technology (and price points). Click here to request a callback.

A Detailed Look At How To Size A Solar Power System

We understand there is a lot of misinformation out there when it comes to sizing up a system, and this isn’t helped by salesmen trying to up-sell customers to large solar systems that they don’t need. So let’s have a look at sizing up a solar system in detail.

Yearly Solar System Output

According to the Clean Energy Council Guidelines, a 5kW system in Sydney should output 19.5 kWh a day on average, or 7117.5 kWh a year. The problem with taking a daily average is that a solar system will output more power in summer and less in winter. This becomes an issue for households that have seasonal usage patterns due to heating, cooling, pool pumps etc. which result in one or two bills a year being significantly more expensive than the others.

5kw solar system output

Air conditioning and pool pumps often work really well with a solar power system, as an increase in power usage over summer is compensated by increased output from the solar system. Contrastingly, heating in winter will often be turned on at night, making it difficult to run off solar. This can be an issue if you just go off the average and expect a 5kW system to give you 20 kWh a day in June when your winter power consumption is predominantly at night.

When do you use your power?

Perhaps this is an obvious statement, but solar power only works during the day. Without battery storage (which is now available), solar power needs to be used in the home as it is generated, otherwise, it automatically feeds out to the grid. You are normally paid around 5-8 cents per kWh by your energy retailer for the power you sell back to the grid – a fraction of what you pay for your power (but at least it’s something). This means the main benefit of solar is to directly reduce your power bill by using it in the home as it is generated.

To find out how much power you use during the day, simply read your meter in the morning and then again in the evening. Subtract one number from the other and that will tell you exactly how many kWh you have used during the day. Ignore the off-peak hot water meter if you have one, and if you have 3 meters for a 3-phase supply, make sure you add the three meters so that you include all of your usage. You may need to take these readings over many days to get a realistic average, rather than at just one point in time.

The other option if you have time-of-use billing is to add the usage during the peak billing period with the shoulder billing period. This will give you your usage from 7 am until 10 pm, which you can then multiply by 0.7 (or so) to give you your daytime usage.

Your Base Load

Every house has a baseload. This will typically include a fridge, freezer, some lights and perhaps some appliances that are left on standby. Like many households in Sydney, no one is home during the day at my place, and we still manage to use 8kWh during the daytime. Divide this number by 4, and a 2kW system would take care of my baseload, saving me around $200 a quarterly bill.

Additional Usage

On top of the baseload, you then have the ability to use appliances during the day. Have a look at the average daily usage figure that is on your power bill – how much of this can you move to the daytime to run on solar power? Without solar power, you may be running appliances at night during the off-peak billing period, or you may be paying little attention to when you use your power as you pay a flat rate for your power. How much power can you use during the day without too much hassle?

The biggest users of power in a typical home include:

  • Pool pumps

  • Spa

  • Air conditioning

  • Heating (can you turn this on with a timer so you come home to a warm house?)

  • Dryer

  • Dishwasher

  • Washing machine

  • Fish Tanks

Generally, we advise not to worry too much about lights when considering solar power. They use very little power compared to the items on the list above and are typically on at night.

Also, keep in mind that your power consumption will often change on the weekend, during the weeks of holidays you have each year and the odd day off from work here and there.

One final point – keep an eye on the future. A surprisingly large number of people we speak to are getting solar now while they are employed, in preparation for retirement or in expectation of a baby, when the mum (or dad!) will be home all day using power.

So how does this compare to the output of a solar power system?

The output of a solar system depends on which way your roof is orientated, and now we are getting into the specifics of maximising the benefit of a solar power installation. The 1KOMMA5° Team will often advise people to go for a split array. Yes, having the panels facing north is best, however, this creates a rough bell curve of output where you get a peak generation period during the middle of the day. Are you going to be able to use most of the solar power most of the time if you have an output curve like in the image below?

This is a 5kW system in March, turning on as the sun comes up and turning off again at around 7 pm. As an aside, one of the most important points from this image is the maximum output. A 5kW system almost never gets close to 5kW of output at any one time due to the angle and the orientation of the panels. This system has produced 959W in 15m, so around 3.8kWh in the middle of the day. This could be improved with sun tracking, however, the cost of installing and maintaining an array that follows the sun does not pay for the increase you will get in output. It is much cheaper to just get a few extra panels.

5kw solar system output sydney

Look at google maps (or get out a compass) to see what roof sections you can install solar panels on. Anything north of west or east is usable.

Panels facing east will output more power in the morning and panels facing west will output power in the afternoon. Compared to North, panels facing east or west will not output quite as much over the course of a year, however, losses are not that great, being more significant in winter when the sun is lower in the sky to the north. The 1KOMMA5° Team have access to detailed aerial photos, and we can accurately measure your roof and provide advice based on that. For more information give us a call today on 1800 052 749. We can help you size up a system in less than 10 minutes.

In most cases, it can be a good idea to have two strings of panels giving you two smaller peaks of output. This makes it easier to use most of the solar power most of the time, and this is how you can maximise the benefit of your system and hence reduce your return on investment.

Do you have time-of-use billing?

Perhaps one of the most important points to consider is how much you pay for your power and when. If you have time-of-use billing, you are much better off generating solar power in the afternoon during the peak billing period. If your panels face west of north, you will push the output of your solar system into the afternoon, and during summer output will continue up until 8 pm. If you have time-of-use billing, we normally say to take an average of 30 cents per kWh when estimating the potential benefit to your power bill.

time of use billing

Do you have shade?

According to Renewable Energy World, shading of as little as 9% of a solar system connected to a central inverter, can lead to a system-wide decline in power output by as much as 54%.

The below image is a great example of how micro inverters can significantly increase output. In this image, the system will be working at near maximum output, despite the patchy shade. With a string inverter, the system will be outputting almost no power because of the panels in the bottom right. I have heard a bit of talk about bypass diodes lately. It is important to state that bypass diodes are designed to help stop hot spots on panels from bird droppings and the like. They do not work in the same way as microinverters and will not help maximise output in shaded conditions like microinverters do.

If you have patchy shade, please call the 1KOMMA5° Team for more information. We have shade analysis tools that can help us provide professional advice on whether you need micro inverters or not, and to what extent shade will impact the predicted output of your system.

Enphase performance reliability shading soiling

How May Solar Panels Should I Buy: A Summary

We hope this information helps you cut through the sales talk. If it all gets too much, just keep it simple; solar can save you around $100 per kW per quarterly power bill and will output around 4 times its size, doing more in summer and less in winter.

In terms of how many panels you will need, compare the different price points and consider whether it is worth looking at a premium panel. There are some real tangible benefits such as a 25-year product warranty, higher efficiency and increased performance to premium panels such as the 1KOMMA5° Full Black Module.

Given this knowledge, you can get a good idea of how much solar power you might need. But remember, this is just a starting point! For a truly customised system designed to maximise your energy savings, there's more to consider.

Check out everything you need to know before investing in solar for your home. This in-depth guide walks you through all the nitty-gritty details to ensure your solar system perfectly fits your home and energy usage pattern.

If you are ready for personalised advice, we are here to help. If you have a few power bills ready, and you have read this article we should be able to help you find the right solution in a matter of minutes.

We work a little differently here at 1KOMMA5°; we help you find the right solution – without any pressure. We want you to make an informed decision and we want you to buy the system that fits your requirements.

Call us today at 1300 525 451 or fill in your details below to request for a solar and home battery storage quote today to see how much you can save!


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