Tools
Rooftop solar yield estimator
Australian home & commercial solar · Southern Hemisphere
Enter one insolation figure from the Bureau of Meteorology for the reference case (north-facing, 23° tilt), and this converts it into an expected daily yield for split arrays across the east, north, west and south faces of your roof, each with its own panel count and slope. It's built for Australian home and commercial solar, using Southern Hemisphere sun-path geometry.
The example is a July estimate for Adelaide with 10 panels on the north roof and 6 on the west. The 3.2 kWh/m²/day figure is an example only, so replace it with your own BOM value.
Location & date
BOM reference insolation
Panels
Roof arrays
West roof
Azimuth
East roof
Azimuth
North roof
Azimuth
South roof
Azimuth
Advanced: sky model parameters
- Monthly energy
- –
- System size
- –
- Panels
- –
Daily output by roof face
| Roof face | Panels | Capacity | Correction | Effective insolation | Daily | Monthly |
|---|---|---|---|---|---|---|
| Total | – | – |
How this is calculated
Your BOM figure is treated as the daily insolation on a plane facing true north at the tilt you entered as the reference (default 23°). For every roof face, the tool numerically integrates the sun's position through the day (declination from the selected month, your latitude, hour angle in 0.5° steps) to work out the angle of incidence on that face and on a horizontal plane, giving a daily beam-radiation ratio Rb.
That's combined with an isotropic-sky diffuse term Rd = (1+cos β)/2 and a ground-reflected term Rr = (1−cos β)/2, weighted by the diffuse fraction and albedo above (Liu–Jordan model), to get a tilt/orientation factor R for the reference face and for each roof face. The ratio of the two scales your BOM figure up or down for each array.
Daily energy per array = effective insolation (kWh/m²/day) × array capacity (kW) × system derate factor, which is the standard "peak sun hours" sizing method. This is a geometric approximation, not a full irradiance simulation. It doesn't account for shading, cloud anisotropy, or panel temperature effects beyond the single derate factor. For a final design, cross-check with PVsyst, PVWatts or your installer's tool.
Latitude and sun-path defaults assume a Southern Hemisphere installation (Australia), so a north-facing roof is the sun-facing reference orientation here. In the Northern Hemisphere, the reference faces south.
Created by Andrew Paton, Senior Solar and Battery Design Engineer, AP Design Labs. Contact: . This tool is the property of AP Design Labs. Figures and estimates are for planning purposes only and are not a substitute for a certified system design.