Question

Calculate the angle of incidence of beam radiation on a surface located at Harrisonburg, VA at 10:30 A.M. (solar time) on February 13, if the surface is tilted 45° from the horizontal and pointed 15° west of south.

Answer 1

First, we need to find n (day of the year)

n = 31 + 13 = 44 ( 31 days for January and 13 days of February)

so,

declination angle, = 23.45 sin (360 (284 + n)/365)

= -13.9

= -14

Hour angle, = -22.5

surface azimuth angle, = 15

Lattitude of Harrisonburg, VA , = 38.54 degree north

The equation used is:

cos = sin sin cos - sin cos sin cos + cos cos cos cos + cos sin sin cos cos + cos sin sin sin

Now, just put the values and solve for

cos = sin-14 sin38.54 cos 45 - sin-14 cos38.54 sin 45 cos15 + cos-14 cos38.54 cos 45 cos-22.5 + cos-14 sin38.54 sin 45 cos-22.5 cos15 + cos-14 sin15 sin 45 sin -22.5

cos = -0.10658 + 0.1292 + 0.4958 + 0.38148 - 0.068

cos = 0 .8319

= 33.7 degree

(PLEASE LET ME KNOW IF THERE IS ANY MISTAKES...THERE WERE SO MANY ANGLES, SO PLEASE LET ME KNOW IF ANY MISTAKE)