Difference between albedo and albedo_const in SSC Module 'irradproc'

  • asifak
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13 Jun 2024 12:27 #13252 by asifak
Hi 
There are two important parameters in Module'irraproc', namely, albedo and albedo_const.

Are both required to be given as input ? What I understand is that 1st one is to be given for every hour. How abut the 2nd one i.e. albedo_const ? how does both effect the result ?

Thanks
 

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  • pgilman
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13 Jun 2024 23:36 #13260 by pgilman
Hi Asif,

Here is a link to the documentation of those inputs in the PySAM documentation:

nrel-pysam.readthedocs.io/en/main/modules/Irradproc.html#PySAM.Irradproc.Irradproc.IrradianceProcessor.albedo

Also see Note 3 under the table in the SAM Help topic "Weather Data Elements": samrepo.nrelcloud.org/help/weather_data_elements.html.

SAM automatically makes decisions about what albedo values to use depending on what is available in the weather file.

Best regards,
Paul.

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  • asifak
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14 Jun 2024 04:45 #13261 by asifak
Thanks for the quick response. Appreciated.

First of all, I understand that value of the parameter 'albedo' in the module 'irradproc' is given on hourly basis. In my previous post, I asked the question because I use the output of the 'irdadproc' into 'pv6parmod' in c# environment (I am not using Python or others).
Now, if parameter 'albedo' is kept zero and value of 'albedo_const' is changed, then dc output of the module 'pv6parmod' does not change. what could be the reason ? 
DC Output of the module 'pv6parmod' changes only if value to the parameter 'albedo' is given. 
 

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  • pgilman
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14 Jun 2024 18:10 #13262 by pgilman
Hi Asif,

Here is a link to the code from the irradproc module that handles 'alb_const': github.com/NREL/ssc/blob/857249a1f29158a03c92270e9bc5a8e6a9552a8d/ssc/cmod_irradproc.cpp#L242

In each time step, the model checks to see if there is albedo data from the weather file. If there is, it uses the albedo value from the weather file. If not, it uses the 'alb_const' value.

If you want to use 'albedo_const' in a given time step, you can set the value of the 'albedo' array element for that time step to an invalid value like -1 to force the model to choose the 'albedo_const' value.

Best regards,
Paul.

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