A 6.6 kW system is the most common home solar size in Australia, and the first question everyone asks about it is how much it will actually make. The short answer: on average, about 24–29 kWh a day in Australia's capital cities, roughly double that on a clear summer day and a third of it on a dull winter one.
Here's where those numbers come from, and how to work out the figure for your own roof.
kW is the size, kWh is the output
A 6.6 kW system's rating is its power: the most the panels can produce at one moment, in ideal test conditions. What you want to know is the energy it produces over a day, measured in kWh. If that distinction is new, start with kW vs kWh. It takes three minutes and makes everything below easier.
Average daily output by city
The Clean Energy Council publishes the average daily output you can expect per kilowatt of panels, averaged over a whole year. Multiply by 6.6 for a 6.6 kW system:
City | Average kWh per kW per day | 6.6 kW system, kWh per day |
|---|---|---|
Perth | 4.4 | 29.0 |
Brisbane | 4.2 | 27.7 |
Adelaide | 4.2 | 27.7 |
Sydney | 3.9 | 25.7 |
Melbourne | 3.6 | 23.8 |
These assume a reasonable, unshaded roof facing north (in the southern hemisphere). The Clean Energy Council's guidance is that a working system should produce at least about 90% of these figures over a full year.
Outside Australia, the same sum works with your local yield:
- United Kingdom: most guides put yearly output at about 850–1,000 kWh per kW of panels, more in the south and less in the north. That's about 2.3–2.7 kWh per kW per day on average, so a 6.6 kW system would average roughly 15–18 kWh a day.
- United States: it varies hugely by state. Estimates based on the US government's PVWatts calculator range from about 1,100 kWh per kW per year in Seattle to 1,800 or more in Phoenix: roughly 3–5 kWh per kW per day, or 20–33 kWh a day for 6.6 kW.
For your exact address, use a free calculator such as PVWatts in the US or PVGIS in Europe and elsewhere, which let you enter your location, roof angle and direction.
Summer vs winter
Those are yearly averages. Day to day, output swings a lot:
- A clear summer day: a 6.6 kW system in most Australian cities can make 30–40 kWh.
- A clear winter day: roughly half that, because the sun is lower and the day is shorter.
- A dull, overcast winter day: under 10 kWh is common.
If you're sizing a battery or planning to charge an EV from the panels, plan around winter as well as the average. It's the difference between "covers my evenings" and "covers my evenings in summer".
How much does it produce per hour?
Output follows the sun: close to zero at dawn, peaking around midday, back to zero at dusk. A 6.6 kW system rarely hits 6.6 kW. On a good day it might peak at around 5–5.5 kW at midday, because:
- Heat: panels lose a little efficiency as they get hot, and in full sun they get very hot.
- Inverter limits: many 6.6 kW systems use a 5 kW inverter, which caps the output at 5 kW (more on that below).
- Angle and direction: panels on east or west roofs peak lower and spread their output across the day.
- Dust, shade and wiring losses each take a few per cent.
So if your app shows a peak of 5 kW, nothing is wrong.
Why 6.6 kW of panels and a 5 kW inverter?
In Australia, a 6.6 kW system usually means 6.6 kW of panels on a 5 kW inverter. Federal incentive rules allow panel capacity of up to 133% of the inverter's capacity, and 5 kW × 1.33 ≈ 6.6 kW. Many electricity networks also limit how much a single-phase home can export, often to 5 kW.
It works because the panels only reach full output for a short time around midday. The extra panels make more power in the mornings, afternoons and on cloudy days, when the inverter has room to spare. You lose a little at the peak and gain more across the rest of the day.
Is a 6.6 kW system enough?
That depends on how much you use, and when. A typical Australian household uses roughly 15–25 kWh a day. But solar only covers what you use while the sun is up, unless you add a battery or shift your usage. Our guide to what size solar system you need works it out from your bill.
The power you don't use is exported to the grid, and the feed-in tariff you're paid for it is usually much lower than the price you pay to buy power. That's why using your own solar is worth more than selling it. See how to read your electricity bill for the numbers. It's also why some people add a home battery, or use the midday surplus to charge an EV at home.
How to check your own system
- Open your inverter's app or display and find the total energy produced for the year (not just today).
- Divide by 365 to get your average daily kWh, then by your system's kW size.
- Compare that with your city's figure in the table above. You should be at or above about 90% of it.
If you're well below, the usual suspects are shading that has grown since installation, a faulty panel or optimiser, or an inverter that's tripping off. A good installer can check it.