The extraterrestrial radiation

Since the Earth’s orbit around the Sun is elliptical, the distance between them varies during the year, causing a ±3.3% fluctuation of the extraterrestrial radiation (Fig. 3). This radiation can be roughly calculated for every day of the year using the following equation:

Io(t )=4Ф) [W/m2]

(3)

e(t) = 1 + 0.033cos(2n n(t )/365)

(4)

where n(t) is the progressive number of the day of the year [1].