Diffuse Sky Model

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csmichels
Topic Author

22 Jan 2015 16:10 #2981 by csmichels

Diffuse Sky Model was created by csmichels

Dears,

I've seen that the new SAM includes the option of calculating POA irradiance using total+diffuse components. Is there any documentation to see what method does it use?

This is very useful, since some times the only data I have available is GHI and DHI (before, i calculated mathematically the beam component using the sun's position and filtering for low cos values).

Thanks

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Paul Gilman

22 Jan 2015 18:56 #2982 by Paul Gilman

Replied by Paul Gilman on topic Diffuse Sky Model

Hello,
The draft PV reference manual available on the Performance Model Documentation page includes a description of the incident irradiance calculations.
Best regards,

Paul.

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csmichels
Topic Author

26 Jan 2015 20:16 #2983 by csmichels

Replied by csmichels on topic Diffuse Sky Model

Dear Paul,

Dear Paul,

I've revised the document but it only explains the two old calculation modes:
- Beam + Diffuse
- Global + Beam

But SAM the new SAM release can do PV calculation using only Global and Diffuse. I could not find any reference for this calculation on that document.

Thanks

Sebastian

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Paul Gilman

26 Jan 2015 21:30 #2984 by Paul Gilman

Replied by Paul Gilman on topic Diffuse Sky Model

Dear Sebastian,

Ah yes. Thank you for the clarification. I did not read your original post carefully enough.

When you run the detailed photovoltaic model in "total and diffuse" mode, SAM uses the following equation to calculate the beam (direct normal) irradiance from the total and diffuse irradiance values in the weather file:

ibeam = (gh - df) / cos(z)

Where ibeam=beam, gh=total horizontal in W/m2 from weather file, df=diffuse horizontal in W/m2 from weather file, and z=sun zenith angle in degrees.

If the result is greater than 1500 W/m2, it sets ibeam = 1500. If it is less than zero, it sets ibeam = 0.

Best regards,
Paul.

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