Updated on March 4, 2026
If you’re looking at solar in Australia, you’ve probably seen 6.6kW systems with 5kW inverters. But why is this setup so common, and is it right for you?
Solar technology changes quickly. A decade ago, 3kW systems were standard. Then 5kW became popular, and now many homes quickly outgrow 6.6kW.
At PSC Energy, we want you to understand exactly what you’re buying so you can make the best decision for your home. We install systems of all sizes, and we’re here to give you some pointers to choose a solar system size.
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’ll see why 6.6kW systems are popular, and how to apply that thinking when sizing a system for your home.
Why Do Solar Companies Sell So Many 6.6kW Systems with 5kW Inverters?
In short, this setup is easy to get approved, helps you get the most from government rebates, and is straightforward for installers to offer widely.
Most single-phase homes in Australia have a 5kW export limit. This means that your grid connection won’t allow more than 5kW to be fed back to the network at any one time.
Installers match a 5kW inverter with 6.6kW of panels because the Clean Energy Council lets you oversize the solar array by up to 133% compared to the inverter. This means more panels, more energy, and no extra approvals.
What does “oversized” actually mean?
This means the panels can produce more power than the inverter’s limit. It might seem odd, but it’s actually a clever design.
Solar panels rarely reach their peak output because the sun isn’t always perfectly overhead; it gets hot, dust builds up, and light angles change with the seasons. By putting slightly more panels on the roof, the inverter runs closer to its full capacity for more hours each day, especially in the early morning and late afternoon. The result is better overall production without exceeding grid limits.
The downside is that many installers use this as a one-size-fits-all solution. They put the same system on every roof without tailoring it to the customer’s real energy needs.
And if a customer wants more capacity, they’ll often just double it: two 5kW inverters, 13.2kW of panels, rather than design something tailored to your unique needs and goals.
The government STC rebate also plays a role. The more panels you install, the more Small-scale Technology Certificates you earn (the bigger your solar panel rebate).
The Clean Energy Council’s 133% rule means 6.6kW is the maximum you can squeeze onto a standard 5kW inverter while still qualifying easily for maximum rebate.
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?
A quality 6.6kW system typically costs around $6,600 after the STC rebate, which is roughly $1 per watt. That’s the current industry average for a well-specified system.
Watch out for quotes that are much higher or lower than average. A very low price often means cheaper panels, a lower-quality inverter, or rushed installation. A much higher price should also make you ask questions.
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.
Roof Real Estate: How Many Panels Are in a 6.6kW System?
Using a 400W panel as a benchmark:
- Number of panels: 6,600W ÷ 400W = approximately 16–17 panels
- Roof space required: ~1.7m² per panel × 17 panels = roughly 28–29m²
If your installer uses lower-wattage panels, you’ll need more of them (and more roof space). Higher-wattage panels mean fewer panels and a smaller footprint.
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?
It’s hard to say exactly without knowing your situation. The main factors are:
- Location — how close you are to the equator affects how much sunlight you get year-round
- Climate — overcast regions produce significantly less
- Panel orientation and tilt — north-facing panels at the right pitch outperform everything else
- Shading — even partial shade can drag down a whole string of panels
- System condition — a poorly maintained or faulty system produces less
- Monitoring — you can only manage what you measure
In ideal Australian conditions, a 6.6kW system can produce about 24 to 28 kWh per day. Your installer should provide an estimate tailored to your roof and postcode, not just a rough guess.
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?
Yes, if your budget allows. For most homes, picking a battery that fits your usual evening and overnight energy use works best. Think about your daily power needs and if you want backup power during blackouts when choosing battery size.
Without a battery, any extra solar energy your home doesn’t use right away is sent to the grid for a low feed-in tariff, often just a few cents per kWh. A battery lets you save that midday extra energy to use in the evening when most homes need power.
For a 6.6kW system, think about a battery between 5kWh and 13.5kWh. Smaller households often pick the Enphase 5P, while bigger families usually go for the Tesla Powerwall 3 or the Sigenergy SigenStor, depending on their storage needs.
The best battery for you depends on how much power you use in the evening and overnight, and if you want backup during blackouts. Talk these points over with your installer to find the right size.
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?
A rough example using Sydney figures:
- Daily household usage: 25kWh
- Electricity rate: ~$0.38/kWh
- Annual grid electricity cost (without solar): ~$3,467
A 6.6kW system costs about $6,600 upfront, and the payback period could be as short as 3 to 4 years if you use most of the solar energy you generate yourself.
Without a battery, most households self-consume only about 60% of what they generate.
Adding a battery raises your upfront cost and lengthens the payback time, but it gives you more energy independence and helps protect against rising electricity prices in the long run.
The truth is, your payback period depends a lot on how you use electricity, your rates, how much solar energy you use yourself, and how well the system fits your home.
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 Up: Reap What You Solar
For many households, a 6.6kW system remains an affordable, grid-compatible, rebate-friendly starting point, well-understood by installers.
But it’s no longer the latest standard. Homes with electric vehicles, big air conditioning needs, or home offices might want a bigger system. As panel efficiency improves, what used to be the “ideal” size is now often the minimum.
The best advice is to talk to an installer who reviews your energy bills, roof, and goals instead of someone who just offers the same system they’ve put on dozens of other roofs.
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 is the inverter only 5kW if the panels are 6.6kW?
Most single-phase homes in Australia have a 5kW export limit. The extra panel capacity improves production throughout the day without exceeding grid rules.
Can I install a solar panel system larger than 6.6kW?
Yes. Larger systems are possible but may require DNSP approval, export controls, or a three-phase connection. Your installer can advise what’s feasible for your property.
Is a 6.6kW solar panel system enough for a family?
For an average Australian household, yes, especially with good self-consumption habits or a battery. For homes with high loads (EVs, large ducted air conditioning, home offices), a larger system may serve you better.
Am I still eligible for a government rebate with a 6.6 kW solar panel system?
Yes. 6.6kW systems fully qualify for the STC rebate. The more panels installed, the larger the rebate.
What battery size suits a 6.6kW system?
Typically, 5-13.5kWh, depending on your evening usage and whether you want blackout protection.
