[Radiance-general] gendaylit

[Ehsan M.Vazifeh]

Dear All,

I am using Perez sky model (gendaylit) in Radiance. When I calculate the
horizontal irradiance and compare it with global irradiance sensor I get
systematic error (rtrace gives around 70% lower values). I checked
everything in between so far nothing was wrong in the code, Here is one
sample:

gendaylit -ang 22.11 -64.30 -W 370.67 108.20 > genday_03_22_07_20.rad

then I add the sky description in the rad file:

skyfunc glow skyglow
0
0
4 1 1 1 0
skyglow source sky
0
0
4 0 0 1 180

void glow groundglow
0
0
4 1 1 1 0
groundglow source ground
0
0
4 0 0 -1 180

then I create an octree file:

oconv genday_03_22_07_20.rad > genday_03_22_07_20.oct

after that using rtrace I calculated the horizontal irradiance which is:
150.718 w/m^2

echo '0 0 0 0 0 1' | rtrace -w -ab 7 -ad 4096 -ar 512 -aa 0.1 -as 64 -I -h
genday_03_22_07_20.oct | rcalc -e '$1=$1*0.265+$2*0.67+$3*0.065'

150.718

but the measured global horizontal irradiance
 (Pyranometer)
is 252.2 w/m^
2

I calculated this output for the whole year but still the Perez is
significantly underestimating the horizontal irradiance. I should add that
I used gensky to generate the same output and results showed gensky
horizontal irradiance fit well with Pyranometer irradiance. Does anyone
have any idea what is wrong here?

Thank you all, Ehsan
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