Illuminance from direct sunlight Evs--Algorithm 1.24

Solar illuminance on a surface is derived from the extra-terrestrial illuminance by calculating attenuation in the atmosphere and the angle of incidence.

a. Solar normal illuminance Evsn

Input
Illuminance turbidity factor, Til (algorithm 1.21)
Relative optical air mass, m (algorithm 1.22)
Extra-terrestrial illuminance, Evo (algorithm 1.23)

Equation
The first expression gives the mean extinction coefficient of light in clean dry air; the second gives the illuminance on a surface at ground level perpendicular to the sun�s beam.

Source
Navvab (1)

b. Solar illuminance on an inclined plane Evs(ak,gk)

Input
Azimuth and altitude of normal to plane (sky point facing plane) ak,gk
or direction cosines n1 n2 n3 (algorithm 6.12)
Solar azimuth and altitude as,gs
or direction cosines c1 c2 c3 (algorithm 1.24)

Equation
References
  1. Navvab M et al. Analysis of atmospheric turbidity for daylight calculations Energy and Buildings 6 293-303 (1984)

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