Updated on July 29th, 2025
In Australia, 6.6 kilowatt (kW) solar systems paired with 5kW inverters are incredibly common. Why is that?
Solar technology is evolving at a very rapid pace, and the truisms that installers could count on just a year or two ago have already been improved and replaced by the latest and greatest tech.
Ten years ago, a 3kW system was standard. Then, for a while, a 5kW system was preferred. And now, our community is outgrowing the 6.6kW system.
At PSC Energy, we want you to understand the ins and outs of the solar industry so you can make the most informed choice possible. It’s important to speak with a reputable solar installer about your needs as you work together to design a system that helps you achieve your energy goals.
In this article, you will learn:
- Why Do Solar Companies Sell So Many 6.6kW Systems with 5kW Inverters?
- How Much Does a 6.6kW System Cost?
- Roof Real Estate: How Many Panels are in a 6.6kW Solar System?
- How Much Energy Does a 6.6kW System Produce?
- Should I Install Solar Batteries with a 6.6kW Solar System?
- How Long is the Payback Period on a 6.6kW Solar System?
- FAQ: 6.6 kW System with a 5 kW Inverter
By the end of this article, you will understand why 6.6kW systems became common and why you might want to take the same principles and apply them as you continue your solar journey.
Why Do Solar Companies Sell So Many 6.6kW Systems with 5kW Inverters?
When we say a solar system is 6.6kW, we’re referring to the power output coming from the solar panels on the roof. A system of that size is usually automatically paired with a 5kW inverter.
Many solar system sales companies will promote this combination. Why is that?
The reason solar sales companies sell a 5kW inverter with 6.6kW of panels is that it’s very easy to get the permission to connect to the grid with those technical specifications.
Export limits for single-phase sites don’t go over 5kW, so they slap 6.6kW of solar on the roof because it’s perfectly oversized at 133% to a 5kW string inverter (we’ll explain what this means shortly).
If a customer wants a larger system, such installers tend not to customise it. They’ll double it with 13.2kW of solar on the roof and two 5kW inverters.
That’s par for the course for a lot of solar systems. Such companies thrive on the repetition of installing this system. They don’t customise the system to match the customer’s needs or goals.
They show up on installation day, they always use a single-phase inverter, and they install cheap systems over and over and over again.
The Clean Energy Council (which makes the rules nationally for solar in Australia) has rules about how solar panels should be paired with inverters.
They do this for a couple of reasons. One of those issues is to protect the electrical grid from too many homes with solar exporting electricity back to the DNSP. But it can handle a maximum of 5kW per household.
There is also the issue of calculating the federal government rebate. The amount of STCs (Small-scale Technology Certificates) a household can receive is proportional to the number of solar panels on its roof and the megawatts those panels can potentially produce.
In order to get as many panels as possible on the roof for maximum solar panel production (and maximum STCs), the Clean Energy Council approved the installation of a 5kW inverter with a 6.6kW system nationwide.
Such an installation is called “oversized” or “overclocked” because the panels are overproducing power for the inverter to convert and send to the home. Why is this advantageous?
Solar panels rarely operate at peak efficiency. Their power rating is verified in a lab with ideal testing conditions. Most of the year, on your roof, solar panels are less efficient.
The reason for that is that the sun does not always shine on your panels perpendicularly year-round. When the sun hits your panels at a perfect 90°, they are at their most efficient.
The sun is lower in the sky in the winter and higher in the sky in the summer. The amount of irradiation varies significantly throughout the year, and so does your solar production.
Another variable that affects the efficiency of your solar panels is heat. Solar panels operate best around 25° on a cool or maybe even windy day. Dust and dirt buildup all obstruct the panel, dropping the efficiency of the system.
Having more panels producing more power keeps the inverter running at a higher average efficiency year-round. You’ll get greater solar energy production in the early morning and late evening because of this as well.
A 5 kW inverter can be oversized by 33% according to the Clean Energy Council requirements. If the solar system outputs more than 6.6kW, the inverter will need an increased capacity if it’s a single-phase site.
But if the inverter is larger than 5kW, it would then no longer be compatible with grid requirements. In this case, you can set the inverter to export 5kW maximum back to the grid.
If you’re interested in learning a bit more about oversizing, you might want to check out the following article titled, Oversizing Your Solar Panel System: How to Maximise Your Panels for Bigger Returns.
How Much Does a 6.6kW System Cost Upfront?
It will cost approximately $1 per watt after calculating the STC rebate, so around $6,600. That’s the overall industry average at the moment for a quality system of that size. However, we’ve seen others advertised at a lower price.
Variables like installation costs can be radically different from installer to installer. There’s also a lot of cheap equipment on the market that doesn’t cost much (it also doesn’t last too long).
You should really be cautious of anyone who promises a 6.6kW string inverter solar system that is significantly higher or lower than around $1 per watt.
If you’re interested in learning a bit more about solar panels and energy systems, you might want to check out the following article titled, Are Solar Panels Worth It in NSW, Australia? A Price Breakdown for 2025.
Shine brighter with solar energy.
Roof Real Estate: How Many Panels Are in a 6.6kW System?
For the sake of this article, we’ll use a 400W solar panel as an example. The math on that is relatively simple to work out:
6,600W / 400W = 16.5 solar panels (approximately)
Obviously, no one installs half a panel. And the 400W estimate for the wattage of a solar panel is not what every installer uses. Some put lower-wattage panels on the roof, and there are more of them. If the panels have a higher wattage, there will be fewer of them.
A solar panel is generally about 1.7m2. So then: 1.7m2 x 16.5 solar panels = 28.05m2
And the estimate of the size will depend on how many panels you’re installing up there. If the panel has less wattage, there will be more of them taking up more roof real estate; if the panels have a higher wattage, there will be fewer of them.
If you’re interested in learning more about how the size of your roof affects your installation, you might want to check out the following article titled, How Does Your Roof Affect Your Installation?
How Much Energy Does a 6.6kW System Produce?
There are just too many factors to consider when looking at energy production for a system.
- Location: The geographic location of your home and solar panels with respect to the Equator has a lot to do with energy production.
- Climate: Is it often overcast? Clouds interfere with a solar system’s ability to harvest that sweet, sweet sunshine.
- Orientation and pitch of each panel: What direction are your solar panels facing? Are they on a southern-facing roof? What time of day is it?
- Shading: As we mentioned with clouds, shading is directly blocking sunlight from hitting those sleek black panels. Solar panels need light.
- Performance of equipment: Is your system working the way it’s supposed to?
- Care and upkeep: Are you taking care of your system? Are you monitoring its energy output and how it interacts with the electrical grid?
How much energy a 6.6kW string system produces is really difficult to even guess without some of the information in a few of these bullet points answered.
If you’re interested in learning a bit more about how weather affects solar panels, you might want to check out the following article titled, How Does The Weather Affect Your Solar Panels?
Should I Install Solar Batteries with a 6.6kW Solar System?
Absolutely, you should.
They’re crucial for getting your home self-consuming your own energy (and we believe in the importance of self-consuming your own energy).
It’s very difficult to maximise the efficiency of your solar investment without a solar battery or two to help you fully self-consume from your solar system.
For a 6.6kW system, you will most likely have excess energy, especially in the middle of the day when the sun is high in the sky and the solar panels are pumping. Without a solar battery, that electricity will be exported back to the grid for pennies per kW.
If you’re interested in solar batteries, you might want to check out the following article titled, Are Solar Batteries Worth It in NSW? PSC’s Ultimate Guide for 2025.
How Long is the Payback Period on a 6.6kW Solar System?
This depends on how much your upfront payment for the system will be, what the cost of your energy bills is, and how much electricity you’re able to self-consume from the solar system.
If a 6.6kW system costs a little over $6,000, then you need to look at your energy bill savings against that upfront price.
Energy in Sydney is around $0.38 per kWh. The higher the price, the shorter your payback period will be (and the cost of electricity is rising).
If your family uses 25kWh per day, then the cost of importing that electricity directly from the grid will be:
25kWh x $0.38 = $9.50 per day
The cost of buying that much energy per year will be approximately:
$9.50 x 365 days = $3,467.50 in energy per year
That looks like your solar will earn back its upfront cost quickly if the system is only a little over $6,000. However, we have not yet factored in how much energy you’re going to self-consume.
This is where things get a little tricky with figures. Without a solar battery, you probably won’t self-consume more than 60% of your solar energy unless you work from home or your needs are incredibly low (but if that were the case, you wouldn’t need solar).
Of course, the cost of a solar battery will increase the upfront cost, extending your payback period.
There are so many factors to consider when figuring out this equation. Our best suggestion is to ask questions and keep a level head as you decide what will be the best solution for your energy needs and goals. Those needs and goals will be different for everyone.
A solar system payback period as short as the timeline we mentioned above depends on a lot of things functioning properly.
If you’re interested in learning a bit more about how to save with solar, you might want to check out the following article titled, Self-Consumption: How to Increase Solar Energy Use.
Wrapping Things Up: 6.6 kW Systems and 5 kW Inverters
Now that you understand why a 6.6kW string inverter solar system is so often paired with a 5kW inverter. The cost, the size, and the specifics of production factor into the decision to install a system of that size.
As energy needs continue to evolve, the standard size of a solar string system will need to evolve as well. It’s the tail-end of the 6.6kW string system’s reign.
At PSC Energy, we want you to be fully informed. Remember to keep your eyes and ears open and ask lots of questions before pulling the trigger on a solar system of any size.
A solar consultant worth their salt will work with you to assess your needs and plan out a system just for you.
If you’re interested in learning more about solar systems, you might want to check out our introductory article titled, New to Solar: Start Here.
FAQ: 6.6 kW System with a 5 kW Inverter
Why are 6.6kW solar systems with 5kW inverters so common in Australia?
6.6kW solar systems paired with 5kW inverters are popular because they meet Clean Energy Council guidelines and DNSP export limits. Most single-phase homes in Australia have a 5kW export cap. Oversizing the panels to 6.6kW (a 133% overclock) maximises energy production without requiring special grid permissions. It’s a sweet spot for efficiency, rebate eligibility, and easy approval.
What does oversizing a solar system mean?
Oversizing a solar system means installing more solar panel capacity than the inverter’s rated capacity. For example, putting 6.6kW of panels on a 5kW inverter. This boosts average daily production, especially in the morning and late afternoon, when sunlight isn’t as direct. Oversizing is legal and encouraged within limits—up to 133% of the inverter rating for single-phase homes under Clean Energy Council rules.
How much does a 6.6kW solar system cost in 2025?
In 2025, a high-quality 6.6kW solar system in Australia costs around $6,600 after the STC rebate. That’s roughly $1 per watt. Some companies advertise cheaper prices, but they often use lower-grade panels or inverters. Always check what’s included in the quote—especially product quality, warranties, and installation costs.
How many solar panels are in a 6.6kW system?
A 6.6kW system typically has around 16 to 18 panels, depending on panel wattage. If each panel is 400W, you’ll need about 16.5 panels—so most systems round up to 17 or 18. The number may vary based on roof space, shading, and orientation. A 6.6kW system using 400W panels requires approximately 28 square metres of roof space.
How much energy does a 6.6kW solar system produce daily?
The daily energy output of a 6.6kW solar system depends on location, panel orientation, shading, and weather. On average, it can produce between 24 and 28kWh per day in sunny Australian conditions. However, results vary widely. Cloud cover, roof angle, and system performance all influence daily output. Your solar installer can estimate more accurately based on your roof and postcode.
Is a 6.6kW solar system big enough for a family?
Yes, a 6.6kW system is suitable for many average-sized Australian households. It can cover much of the daily energy use if paired with good self-consumption habits or battery storage. For homes with high energy needs—like EV charging, large aircon systems, or home offices—a larger system may be better.
Should I install a solar battery with my 6.6kW solar system?
Yes, installing a solar battery with your 6.6kW system helps maximise your energy savings. Most homes will produce excess energy in the middle of the day. Without a battery, that energy is exported for a low feed-in tariff. With a battery, you can store it and use it later at night or during blackouts. This boosts self-consumption and makes your system more efficient long-term.
What size solar battery pairs best with a 6.6kW system?
A battery between 5kWh and 13.5kWh works well with a 6.6kW system, depending on your energy usage patterns. Smaller homes might benefit from a 5kWh battery like the Enphase 5P. Larger households may prefer a Tesla Powerwall 3 or a Sigenergy SigenStor. The best choice depends on how much energy you use at night and whether you want blackout protection.
How long is the payback period for a 6.6kW solar system?
The average payback period for a 6.6kW solar system is 3 to 6 years, depending on energy use, solar self-consumption, electricity rates, and battery inclusion. If you self-consume more energy and avoid high grid rates (about $0.38/kWh in Sydney), you’ll recoup your costs sooner. Batteries extend the payback period but offer greater independence and stability over time.
Can I install more than 6.6kW of panels on my home?
Yes, you can install more than 6.6kW of solar panels, but there are extra considerations. Larger systems may require DNSP approval, three-phase power upgrades, or multiple inverters. Export limits may still apply, so you may need to cap your export at 5kW on single-phase sites. Your installer will help assess what’s allowed and what’s best for your energy goals.
Why is the inverter size limited to 5kW for single-phase homes?
Most single-phase homes in Australia have a 5kW export limit set by DNSPs to protect the grid. Installing a larger inverter would require special export controls or upgrades. A 5kW inverter with 6.6kW of panels meets this requirement while producing strong output across the day. This balance makes approval fast and installation more affordable.
Can I still get a government rebate with a 6.6kW solar system?
Yes, 6.6kW systems are fully eligible for the STC (Small-scale Technology Certificate) rebate in Australia. The rebate value depends on how many panels you install and your geographic zone. The more panels (kW), the bigger your rebate. That’s one reason 6.6kW is so common—it maximises the STC rebate without pushing beyond grid limits.
What’s the difference between a 5kW and a 6.6kW solar system?
A 5kW system refers to the inverter size, while 6.6kW refers to the total panel output. A 6.6kW system is essentially a 5kW inverter paired with an oversized panel array to improve performance. You get better production throughout the day, especially during low-light hours. The extra panel capacity helps you make the most of your 5kW export allowance.
Is a 6.6kW solar system still worth it in 2025?
Yes, a 6.6kW system is still a good starting point in 2025 for homes with moderate energy needs. It’s affordable, STC-rebate friendly, and grid-compatible. However, homes with growing energy needs or plans for EV charging might want to future-proof with a larger system. As panel efficiency increases, 6.6kW may soon be the new minimum rather than the ideal.
