5kW vs 6.6kW Solar System: Cost, Output, Inverter Differences & Which Is Better?
Reviewed by Bidhan Bhuson Roy
Choosing between a 5kW and 6.6kW solar system is one of the most common sizing decisions Australian homeowners face. While the two systems look similar on paper, the difference in output, inverter pairing, and long-term savings can be significant.
In most cases, the 6.6kW system has become the standard choice across Australia because it delivers more energy for only a modest increase in upfront cost.
Below, we break down the real differences so you can decide which solar system size suits your home.
Table of contents
What is the difference between a 5kW and 6.6kW solar system?
A 6.6kW solar system has 1.6kW more panel capacity than a 5kW system and typically produces 20–30% more electricity per day, while often costing only $800–$1,500 more installed in Australia.
The key differences are:
- Panel capacity – 6.6kW has more solar panels.
- Energy production – 6.6kW generates more kWh per day.
- Inverter pairing – both systems commonly use a 5kW inverter.
- Cost per watt – 6.6kW usually offers better value.
Quick comparison
| Feature | 5kW System | 6.6kW System |
|---|---|---|
| Typical Panels | 12–14 | 16–18 |
| Daily Output | 18–22 kWh | 24–28 kWh |
| Typical Cost | $4,500–$6,000 | $5,500–$7,500 |
| Inverter Size | 5kW | 5kW |
| Best For | Small homes | Most Australian homes |
The reason the 6.6kW system became dominant in Australia is simple: you get substantially more energy production without needing a larger inverter. That makes the marginal upgrade cost relatively small compared to the additional output.
This leads directly to the next question — how much more electricity does it actually produce?
How much electricity does a 5kW vs 6.6kW system produce per day?
In most Australian capital cities, a 5kW system produces around 18–22 kWh per day, while a 6.6kW system produces 24–30 kWh per day, depending on location, roof angle and orientation.
Actual production depends on:
- City and climate
- North vs east/west orientation
- Roof pitch
- Shading
- Panel efficiency
Estimated daily output by city
| City | 5kW (kWh/day) | 6.6kW (kWh/day) |
|---|---|---|
| Sydney | 19–21 | 25–28 |
| Brisbane | 21–23 | 27–30 |
| Melbourne | 17–19 | 22–25 |
| Adelaide | 20–22 | 26–29 |
Over a full year, that extra 1.6kW of panels can generate roughly 1,500–2,000 additional kWh annually, depending on location.
That additional energy is what improves the financial return — especially if you use electricity during the day.
But how does a 6.6kW system use the same inverter as a 5kW system?
Can you use a 5kW inverter with a 6.6kW solar system?
Yes, in Australia a 6.6kW solar system is typically paired with a 5kW inverter because regulations allow up to 133% DC oversizing.
This is called DC oversizing.
- The panels (DC) total 6.6kW.
- The inverter (AC) is rated at 5kW.
- The DC/AC ratio is about 1.32.
This setup works because solar panels rarely operate at peak output for extended periods, meaning the inverter is not constantly limiting production. Oversizing improves energy generation in the early morning and late afternoon, while small amounts of midday clipping have minimal impact over a full year.
What is the cost difference between a 5kW and 6.6kW system?
In 2026, upgrading from a 5kW to a 6.6kW system usually costs only $800–$1,500 extra because the inverter remains the same, and the upgrade involves adding only a few additional panels.
Most of the system cost sits in:
- Inverter
- Installation labour
- Mounting hardware
- Compliance and certification
Since those components stay the same, upgrading primarily means adding 4–6 extra panels.
Cost per watt comparison
| System | Typical Price | Price Per Watt |
|---|---|---|
| 5kW | $5,000 | $1.00 |
| 6.6kW | $6,200 | $0.94 |
The larger system often has a lower price per watt, which improves overall value.
This is where the upgrade argument becomes practical rather than theoretical.
Is it worth upgrading from 5kW to 6.6kW?
For most Australian homeowners, upgrading from 5kW to 6.6kW is financially worthwhile because the additional 1.6kW of panels typically pays for itself within 2–4 years.
Let’s look at a simplified example.
If the 6.6kW system generates an extra 1,800 kWh per year:
- Self-consumed at $0.30/kWh = $540 per year
- Exported at $0.08/kWh = $144 per year
Even with partial self-consumption, the extra energy often delivers $400–$600 per year in additional value.
💡Pro tip: Check out the 6.6kW vs 10kW solar system to oversize for future electricity use.
What size household suits 5kW vs 6.6kW?
A 5kW system suits homes using 18–24 kWh per day, while a 6.6kW system better suits homes using 22–28 kWh per day or planning to electrify appliances.Â
This translates to an average 3 bedroom house. If you have a pool and ducted air conditioning, then a 6.6kW would probably be better suited.
Should you choose 5kW or 6.6kW?
Most Australian households should choose 6.6kW unless roof space is limited or electricity usage is unusually low.
Choose 5kW if:
- Your roof cannot fit more panels.
- You use very little daytime electricity.
- Budget is the overriding constraint.
Choose 6.6kW if:
- You have roof space.
- You want stronger long-term savings.
- You plan future electrification.
- You want better cost per watt value.
Because the inverter is typically the same size in both systems, the upgrade from 5kW to 6.6kW is often one of the most cost-effective increases in system capacity available.
FAQs
Will a 6.6kW system export more power?
Not necessarily. Many network operators cap exports at 5kW, but the larger system increases self-consumption and overall production.
Is a 6.6kW system too big for a small home?
It can be oversized for very low-usage households, but for most homes it provides flexibility and futureproofing.
What happens if panels are oversized?
The inverter may clip small amounts of peak power at midday, but annual energy generation is typically higher than a 5kW panel system.
Can I expand a 5kW system later?
Expansion can be limited by inverter capacity and design constraints. Installing the correct size upfront is usually more cost-effective.
