The quantity G

Anton Driesse
Topic Author

06 May 2022 12:59 #10934 by Anton Driesse

The quantity G was created by Anton Driesse

G is defined in the manual (2018) eq. 7.8 and then appears to be redefined in eq. 10.25. Which of these quantities is used as input to the NOCT thermal model eq. 10.37?

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Paul Gilman

06 May 2022 22:20 #10939 by Paul Gilman

Replied by Paul Gilman on topic The quantity G

Hi Anton,

This is a question about the Photovoltaic Reference Model .

The source code for Equation 10.37 for NOCT Cell Temperature model's cell temperature is here: github.com/NREL/ssc/blob/b130bde3f3fbe8a825891bc994983b8339bc2c91/shared/lib_cec6par.cpp#L217

The G in the manual's Equation 10.37 is G_total in in the source code.

G_total depends on various options here: github.com/NREL/ssc/blob/b130bde3f3fbe8a825891bc994983b8339bc2c91/shared/lib_cec6par.cpp#L173

Best regards,
Paul.

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Anton Driesse
Topic Author

09 May 2022 10:19 #10942 by Anton Driesse

Replied by Anton Driesse on topic The quantity G

Hi Paul,

While the open code references could be useful to see what the SAM is actually doing, I f possible would prefer to have a simpler answer just stating how the documentation should be interpreted and saying what SAM is intended to do.

Best regards,
Anton

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Paul Gilman

09 May 2022 23:20 #10945 by Paul Gilman

Replied by Paul Gilman on topic The quantity G

Hi Anton,

It's a bit complicated because the value of "G" shown in Equation 10.37 of the Photovoltaic Reference Manual depends on a couple of options in the SAM user interface. It represents the effective irradiance on the cell after the sun's light has passed through the module cover:

If you are using a weather file where the solar irradiance data represents irradiance incident on the earth's surface or irradiance measured in the plane of the array (POA) by a pyranometer, then SAM adjusts G from Equation 7.8 as shown in Equation 10.25.

If you are using a weather file with POA irradiance data, where the data is from a reference cell in the plane of the array, then SAM uses the POA data from the weather file without adjusting it.

Best regards,
Paul.

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Anton Driesse
Topic Author

10 May 2022 09:40 #10947 by Anton Driesse

Replied by Anton Driesse on topic The quantity G

Thanks very much, Paul. That seems pretty clear.

Best regards,
Anton

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Anton Driesse
Topic Author

22 May 2022 14:45 - 23 May 2022 19:46 #10983 by Anton Driesse

Replied by Anton Driesse on topic The quantity G

Hi Paul,

Is it possible that Equation 10.25 in the documentation is missing a subscript 'o' on the left hand side?

It seem to correspond ot this line of code:

Geff_total *= air_mass_modifier( theta_z, input.Elev, amavec );

Best regards,
Anton

Last edit: 23 May 2022 19:46 by Anton Driesse. Reason: Wrong equation number

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