Methodology
Every recommendation is computed from first principles and public scientific datasets. Here is exactly how.
Solar geometry
The sun's position (azimuth and elevation) is computed with the NOAA solar equations, based on Jean Meeus' Astronomical Algorithms — accurate to a few hundredths of a degree for the years 1900–2100. Sunrise and sunset use a zenith of 90.833° to account for atmospheric refraction and the solar disc, and are accurate to about one minute. All computations use the timezone of the selected location, never your device's timezone.
Irradiation data
Long-term monthly irradiation comes from PVGIS (European Commission Joint Research Centre), with NASA POWER climatology as a fallback. If neither service is reachable, a clear-sky analytical model provides a clearly-labeled low-confidence estimate.
Finding the optimum
Monthly irradiation is expanded into an hourly profile (Collares-Pereira & Rabl for global, Liu–Jordan for diffuse) and projected onto candidate panel planes with the Hay–Davies anisotropic transposition model, using a ground reflectance of 0.2. The recommended azimuth and tilt are the ones that maximize annual irradiation on the panel — a full-circle data-driven search, not a rule of thumb.
True north, not magnetic
All directions refer to true (geographic) north. The magnetic declination shown alongside results comes from the World Magnetic Model, so you can convert to a compass bearing.
Known limitations
- Local shading from trees, buildings and terrain is not modeled.
- Results are for the front side of a fixed mount; trackers and bifacial gains are not included.
- Very local microclimates may differ from the satellite-derived averages.
- Snow, soiling and temperature losses are not included in irradiation figures.