Assistance with DMEG Module Parameters and .PAN File in PVLIB

[Ludivine Chabaud]

Hi everyone,

I’m working with a DMEG module, specifically the DM640G12RT-B66HSW model. Unfortunately, this module isn’t listed in the CEC or SANDIA databases.

To proceed, I planned to use a .PAN file from PVSYST to fill in the required parameters. However, I’ve encountered an issue where three critical parameters seem to be missing:

• a_ref: Diode ideality factor [float]
• I_L_ref: Light/photogenerated current at reference conditions (A) [float]
• I_o_ref: Diode saturation current at reference conditions (A) [float]

I tried using cross-multiplication to estimate these values, but that approach hasn’t been successful, especially since I couldn’t find any other DMEG models in existing databases to use as a reference.

Here are my main questions:

1. I’m aware that the latest version of PVLIB includes a new function in IO tools that can read .PAN files. However, I’m unclear on how missing values are handled by this function. Could it be that the parameters I’m looking for are present in the .PAN file under different names or in a different format?

2. Is there any document, guide, or resource that explains the terminology used in .PAN files and maps it to the equivalent parameters in PVLIB?

3. If the required parameters are indeed missing, are there alternative methods or tools I can use to derive these values accurately?

I’d greatly appreciate your insights and any resources you can share.

Thanks for your time!

Ludivine Chabaud

[cwh...@sandia.gov]

Hi Ludivine,

1. The pvlib function reads the file into the python workspace but doesn't interpret the content to pvlib quantities. It is possible that the parameters you are missing are in the file. It is also possible that the missing values are being calculated when PVsyst is run.

1a. I'm a little confused that you ask for a_ref, which is a parameter for the CEC model, instead of gamma_ref, the pvlib name for the diode factor in the PVsyst model. Are you trying to derive the parameters for the CEC model functions from the PAN file?

2. There is not, at least that I know of. Complete documentation of a PAN (and OND) file has been wished for a long time. 

3.    I_L_ref = Isc * (1 + Rs / Rshunt) is a common estimate. Estimating the other two, given I_L_ref, Rs and Rshunt, is more complicated, and there are lots of proposed methods in literature. PVsyst appears to solve a series of optimization problems, each giving I_L_ref, gamma_ref and I_o_ref, for a range of values of Rs, and chooses the solution which minimizes a current residual. See the middle of this page: https://www.pvsyst.com/help-pvsyst7/index.html?pvmodule_parameters.htm

If you can run PVsyst and get output at the IEC 61853 conditions (or a similar range of conditions), we recently added pvlib.ivtools.sdm.fit_pvsyst_iec61853_sandia_2025. The function will return a set of parameters for the PVsyst model that reasonably reproduce the input data. The parameters will almost certainly vary from those in the PAN file.

Or, if you have a datasheet for this module, you can try pvlib.ivtools.fit_cec_sam and then use the CEC model.

Best regards,

Cliff