The algorithm to used to determine if a station's value makes sense or not is described in the tables below :



Rules for choosing the interval of acceptance for daily irradiation data
conditions :		upper limit	lower limit
sun at noon >= 2 deg above horizon		1.1 Gc G0	0.03 G0
sun at noon < 2 deg  above horizon	G0 >= 2.78 Wh/m2	2 Gc	0.015 G0
	G0 < 2.78 Wh/m2	27.78 Wh/m2	0.0 Wh/m2





Rules for choosing the interval of acceptance for hourly irradiation data
conditions :		upper limit	lower limit
sun at noon >= 2 deg above horizon		1.1 Gc G0	0.03 G0
sun at noon < 2 deg  above horizon	G0 >= 2.78 W/m2	2 Gc	0.015 G0
	G0 < 2.78 W/m2	27.78 Wh/m2	0.0 Wh/m2


Legend :
G₀ : calculated daily or hourly extraterrestrial value incident on horizontal surface
G_c : calculated daily or hourly clear sky irradiation value
noon : solar elevation at noon true solar time

Extraterrestrial model

The extraterrestial solar radiation is being calculated with a solar constant of I₀ = 1367.0 W/m² and Earth's orbit eccentricity correction. It's the radiation incident on a horizontal surface.

Clear sky global irradiation model

The model being used to calculate Gc is the model developed in the course of the construction of the 4th version of the European Solar Radiation Atlas. Details can be found in the following article: Rigollier C., Bauer O., Wald L., 2000. On the clear sky model of the 4th European Solar Radiation Atlas with respect to the Heliosat method. Solar Energy, 68(1), 33-48.