The quantity G

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?

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.

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

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.

Thanks very much, Paul.  That seems pretty clear.

Best regards,
Anton

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:

Best regards,
Anton