May I ask whether the coefficients (sky clearance and brightness) of the Perez model would be adjusted when I chose a different location (weather profile)? 

Or only the sun hour and other climatic profiles would change if I chose a different location. 


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Hi Ivan,

We call the gendaylit program to handle all of this. The link describes all of the assumptions in the model parameterization reasonably well.



Thanks Alstan, 

I have tried to read the document you mentioned. However, I cannot find the part that explains whether the coefficients are adjusted according to the location. It only stated that the data are from radiometric measurement centres. 


Hi Ivan,

I think the relevant part is here:

The  atmospheric  conditions  are  modelled  with  the  Perez  et  al.  parametrization  (see  Solar  Energy  Vol.  44, No 5, pp. 271-289, 1990), which is dependent on the values for the direct-normal and the diffuse-horizontalirradiances. The three parameters are epsilon, delta and the solar zenith angle. "Epsilon variations express the  transition  from  a  totally  overcast  sky (epsilon=1)  to  a  low turbidity clear  sky (epsilon>6);  delta  varia-tions reflect the opacity/thickness of the clouds". Delta can vary from 0.05 representing a dark sky to 0.5 for a very bright sky.



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