gendaylit in DIVA 2.0 seriously underesitmates total irradiation?

Hi, DIVA list, I found that the gendaylit come with DIVA2.0 seems to seriously underestimate global irradiation.

For example, in Singapore's epw weather file, for Jan 1 9am:

global horizontal irradiation is 152 Wh/m^2

direct normal irradiation is 70 Wh/m^2

diffuse horizontal irradiation is 130 Wh/m^2

Use the gendayilt in C:\DIVA\DaysimBinaries (51KB in size), I can only get 94.07851 Wh/m^2 for an unobstructed upward sensor, which is far lower than the 152 Wh/m^2 as recorded in the weather file and seems to be way off the line... (script is shown in the end of this post). This underestimation seems to be consistent for whatever time, day and city specified.

However, I have an older version of gendaylit (47KB in size) which can produce an unobstructed global horizontal irradiation of 157.5287 Wh/m^2 which is quite close to the value recorded in the weather file. (this older version of gendaylit might come from Radiance 3.9 package)

I'd like to ask:

1) whether the gendaylit.exe come with DIVA2.0 has been modified and recompiled, and what the changes are?

2) why there's such a huge difference in the irradiation as predicted?

(the two different versions of the gendaylit.exe are attached for your reference)



1) the content of the ./sky.rad file:

!gendaylit  1 1 9 -a 1.37 -o -103.98 -m -120 -W 70.0 130.0 -O 1
skyfunc glow sky_glow
4 1 1 1 0
sky_glow source sky
4 0 0 1 180

2) the content of the autorun.bat file

oconv ./sky.rad > ./sky.oct
echo 0 0 0 0 0 1 | rtrace -w -h -I+ -ab 1 ./sky.oct | rcalc -e "$1=$1*0.265+$2*0.670+$3*0.065" > ./results.txt

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Hi, Alstan, noted with many thanks!

- Cheers, Ji

Hi Ji and Alstan,

I'm  a new DIVA user. I found this discussion by searching "gendaylit", however i could't find any guides about how to do it .

could you please give me some advice on it or recommand some teaching material?


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