How the forecast works

We take the weather of your location from the EU's free PVGIS service (satellite data over many years) and compute how much energy standard panels would make on your roof.

If PVGIS is not reachable, an offline model built from NASA POWER climate data for Iran answers instead. It is within about 10 % of PVGIS in our tests, and the result page says which one was used.

Limits

• The numbers are for a typical year. A real year can be higher or lower, which is why we show a range.
• Dust, shade, snow and installation quality can lower the real output.
• Accuracy is lower on the Caspian coast and in the cold north-west.