What Solar Panels Really Make on a Dayboro Roof: A Worked Estimate

Every solar quote we have seen comes with a nice round number for what the system will make. Our question was simpler. What does the sun actually deliver onto a roof in Dayboro, measured here, and what does that turn into once you put real panels under it? So we went to our own weather station, pulled twelve months of solar radiation readings, and did the sums in the open. If you want a forecast for your own roof instead of an annual average, our solar panel calculator does that for the coming days, with your tilt, orientation and system size.

Where our numbers come from

Our station logs solar radiation every five minutes, in watts per square metre on a flat sensor. Add those readings up over a day and you get the energy that landed on one square metre of ground, in kWh/m². That daily total is called insolation, and it is the raw fuel for any solar estimate.

We used October 2025 to September 2026, the last twelve full months. Two honest gaps. The radiation sensor recorded nothing for all of October 2025, so for that month we used the SILO gridded data for postcode 4521, produced by the Queensland Government. In November we only counted the 20 days with a complete record. Every other month uses complete station days only, 316 days in total.

Monthly sunlight on a Dayboro roof

Here is the average daily insolation per month, next to the SILO grid figure for 4521 so you can see both.

Over the full year that comes to about 1,656 kWh per square metre, or 4.54 kWh/m²/day on average (station months, with SILO filling October). The best single day we recorded was 8.84 kWh/m² in December. The worst was 0.73 in March, a properly grey day.

One thing stands out. Our station reads lower than the SILO grid in every month, by about 4% in December and by about 22% in June. We can’t tell you yet if that is the valley, the sensor, or both. A grid model smooths over local terrain, and in winter our mornings often start under fog that the hills hold in. We wrote about that effect in why Dayboro’s valley microclimate affects your solar panels. A sensor that reads a bit low would eventually give the same pattern, so we treat the gap as a question, not a finding.

The worked estimate, step by step

The formula is short:

Daily energy (kWh) = system size (kW) × insolation (kWh/m²/day) × performance ratio

This works because a panel’s kW rating is measured under 1,000 W/m² of sunlight. So each kWh/m² of insolation is worth one “full sun hour” at rated output. The performance ratio (PR) is the share of that you keep after heat, wiring, dust and the inverter take their cut. A well designed and properly working system should sit between 0.75 and 0.85, according to Energy Matters. We used 0.80, the middle. That’s our assumption, not a measurement of anyone’s roof.

For a 6.6 kW system, the most common size we see quoted around here:

Take June as the example: 6.6 × 2.50 × 0.80 = 13.2 kWh a day. Add the months together and the year comes to roughly 8,745 kWh, which is about 24 kWh a day on average, or 3.63 kWh per kW per day.

Look at the spread. December makes about 2.7 times what June makes. That matters more than the annual total, because winter is when the heater and the dryer run and the days are short. If you size a system on the annual average, you’ll feel short in the cold months.

How does that compare with the official figure?

The Clean Energy Regulator puts postcodes 4498 to 4719, which includes Dayboro’s 4521, in Zone 3. Zone 3 has a rating of 1.382, which is MWh per kW per year. That works out to 3.79 kWh per kW per day, or about 9,121 kWh a year for 6.6 kW. Our estimate lands about 4% below it.

Keep in mind what that zone rating is for. It sets how many small scale technology certificates (STCs) a new system earns, the rebate. It’s a deeming figure covering a large stretch of Queensland, not a promise for your roof. If we run the same sum on the SILO grid instead of our station, we get 5.01 × 0.80 = 4.01 kWh per kW per day, above the zone figure. So depending on whose sunlight you trust, a 6.6 kW system around here makes somewhere between 8,700 and 9,700 kWh a year at PR 0.80. On this moment our own measurement sits at the bottom of that range.

What this estimate leaves out

• Roof angle and direction. Our sensor is flat. Panels tilted toward the north catch more of the low winter sun than a flat surface does, so winter output on a well angled roof can beat the table. Panels facing east or west usually make less.
• Shade. A tree or a hill that hides the sun for the first hour costs real kWh, and in a valley that is common.
• Panel age. Panels lose a little output every year.
• Your real PR. A hot roof in January, a dirty array or a small inverter can push it below 0.75.

Well, this is where the calculator earns its keep. Our solar panel estimator takes your tilt, the direction each string faces, your panel type and the age of the system, and runs them against the Dayboro Model forecast for the days ahead. It shows the output at nameplate rating from the sunlight forecast for your roof angle. Multiply by your own performance ratio, 0.80 is a fair start, to get close to what the inverter will show. Members can save their setup and get a daily forecast through My Solar Forecast, handy if you want to plan the washing or a car charge in the weekend. The current sunlight and the rest of our live readings are on the weather hub.

FAQ

How much will solar panels produce in Dayboro?

On our measured sunlight and a performance ratio of 0.80, a 6.6 kW system makes about 24 kWh a day on average, from around 13 kWh in June to around 35 kWh in December. That is roughly 8,700 kWh a year.

How many kWh per kW per day should I expect in Queensland’s south east?

Our station gives 3.63 kWh per kW per day at PR 0.80. The Clean Energy Regulator Zone 3 rating works out to 3.79. The SILO grid for 4521 gives 4.01. A figure of 3.6 to 4.0 is a fair planning range for a well set up roof around here.

Is a Brisbane solar estimate good enough for Dayboro?

For a rough annual number, yes, it is in the same zone. For winter, be careful. Our station reads up to about 22% below the regional grid in June, so a Brisbane figure can flatter the cold months. Check your own roof with the calculator before you size for winter loads.

Sources: Dayboro weather station solar radiation, October 2025 to September 2026, complete days only. SILO gridded climate data for postcode 4521, Queensland Government, CC BY 4.0. Clean Energy Regulator, Postcode zone ratings and zones for solar (photovoltaic) systems. Energy Matters, “Is your solar system underperforming?” (performance ratio range).