Gridly
Peak Sun Hours
The number of hours per day when solar irradiance averages 1,000 W/m² - the standard used to estimate annual solar generation. A 6.6 kW system with 4.5 peak sun hours generates roughly 29 kWh/day on average.
What it means in practice
“Peak sun hours” is a shorthand for the total daily solar energy resource, expressed in a way that’s directly useful for calculating system output. Instead of describing irradiance as a varying curve throughout the day, peak sun hours converts the total daily energy into an equivalent number of hours at STC (1,000 W/m²).
For example: Sydney receives roughly 4.2 peak sun hours per day on an annual average. That means the total irradiance hitting a north-facing, optimally-tilted surface in Sydney is equivalent to 4.2 hours at peak 1,000 W/m² intensity. A 6.6 kW system in Sydney therefore generates approximately:
6.6 kW × 4.2 hours × 0.80 (system efficiency) ≈ 22 kWh/day average
The 0.80 system efficiency factor accounts for inverter losses, wiring, soiling, and temperature derating.
Peak sun hours by Australian city
These are annual averages - summer months significantly exceed these figures, winter months fall below:
| Location | Peak sun hours/day |
|---|---|
| Darwin / NT | 5.8 |
| Perth / WA | 5.5 |
| Alice Springs | 6.0 |
| Brisbane / QLD | 4.8 |
| Adelaide / SA | 5.0 |
| Canberra / ACT | 4.3 |
| Sydney / NSW | 4.2 |
| Melbourne / VIC | 4.5 |
| Hobart / TAS | 3.9 |
Why the number varies
Peak sun hours are an annual average of daily variation. In Melbourne in June, peak sun hours might drop to 2.5–3.0/day. In December, they can reach 6.0+. System sizing and payback calculations use the annual average, but it’s worth understanding that winter generation is substantially lower - particularly relevant if you’re sizing storage or assessing whether solar alone covers your needs year-round.
Roof orientation and tilt also affect the effective peak sun hours your specific system sees. A due-north roof at the optimal tilt angle captures the most energy. East or west orientations reduce effective peak sun hours by roughly 15–20%. South-facing roof sections in Australia generate substantially less than north-facing.
How installers use it
CEC-accredited designers use the peak sun hours data from the Bureau of Meteorology’s PVGIS or similar databases to produce accurate yield estimates for specific sites. A properly designed solar quote should include a simulated annual generation estimate in kWh, not just a kWp figure, with the calculations based on actual site data rather than generic city averages.