Question

Calculate the direct solar incidence angle on a vertical wall facing North-East (NE) for the following given data: (all angles in degree); Latitude angle (1) = 21.54 N, Longitude angle (L) = 39 E, Standard Longitude angle (LSTD) = 45 E, Day: 21st July, Time (Local Civil Time): 15:00. Attach File

Answer 1

Solution:

Direct Solar Incidence angle = cos^-1 [cos⁡(a_M ).cos⁡(a_S ).cos⁡(A_M-A_S )+sin⁡(a_M ).sin⁡(a_S )]

where

a_M = 90° - θ_M = Angle of the wall = 90° - 90° (vertical surface) = 0°

a_S = altitude of the sun = 30° ( on 21st July @ 15:00 - considering hour angle of 30°)

A_M = azimuth of the module = LSTD-L = 45° - 39° = 6°

A_S = azimuth of the sun = Latitude of Surface = 21.54°

Direct Solar Incidence angle (DSIA) = cos^-1 [cos⁡(a_M ).cos⁡(a_S ).cos⁡(A_M-A_S )+sin⁡(a_M ).sin⁡(a_S )]

DSIA =cos^-1 [cos⁡(0°).cos⁡(30°).cos⁡( 6°- 21.54° )+sin⁡(0° ).sin⁡(30° )] = cos^-1 ( 0.8343) = 33.457°