marianne.hartung Posted December 6, 2012 Share Posted December 6, 2012 I am trying to create a PAN File for a PV module where I don't know the IV curve at STC. My Gref and Tref in the "Definition of a PV module > Basic data" sheet are 800 W/m² and 45°C. In this case it seems that the "temperature correction on Gamma" tool does not work correctly. I will give you an example so that you will be able to reproduce my problem. I select "Tools>PV modules" and in "Choosing a PV module" I choose "50 Wp 25 V, Si-poly, CS 50, Centennial Solar, Photon Mag. 2009". In a first step I retreive the performance of this module at 800 W/m² and 45° from the "Definition of a PV module > Basic data > internal model result tool". I obtain Impp = 2.2 A, Isc = 2.42 A, Vmpp = 16.3 V, Voc = 20.2 V, Tc = -0.49 %/°C. Now I try to create a new PAN File for the CS 50 module based on this information. In "Definition of a PV module > Basic data > Manufacturer specifications or other Measurements" I enter Gref = 800 W/m², Tref = 45°C, muIsc = 1.2 mA/K, and the values for Impp, Isc, Vmpp, Voc. Then I go to the "Definition of a PV module > Model parameters > Temper. coeff" sheet and check that the temperature coefficient at STC is set to -0.43%/°C. The corresponding "Gamma temp. coeff" is -0.04 %/°C. If I go back to "Definition of a PV module > Basic data > Internal model result tool", I get -0.44 %/°C at 1000 W/m² and 25°C. First I suspected that this special set of one diode model parameters somehow resulted in a minimum temperature coefficient of 0.44 and smaller values could not be achieved. Therefore I tried putting -0.44%/°C in the "Definition of a PV module > Model parameters > Temper. coeff" sheet. I expected that the gamma temperature coefficient should not change and I would again get the -0.44 %/°C in the "Definition of a PV module > Basic data > Internal model result tool". However, this was not the case. For -0.44%/°C in the "Definition of a PV module > Model parameters > Temper. coeff" I get a "Gamma temp. coeff" of -0.07%/°C and a temperature coefficient of -0.45 %/°C at STC from the "Definition of a PV module > Basic data > Internal model result tool". Can you help? Thanks a lot in advance! Link to comment Share on other sites More sharing options...

André Mermoud Posted January 6, 2013 Share Posted January 6, 2013 First, I observe that your values are quite close. However I can make several comments:- A model is never the reality. Especially the one-diode model is highly non-linear. You establish it at STC (1000 W/m2 and 25°C) and at other conditions (derived from the model), with probably rounding errors in the Isc, Voc, Imp, Vmp values. Therefore this is not exactly the same model's parameters. - The true Pmpp value is not perfectly linear with the temperature: that is, muPmpp it is not constant with the temperature. This is a result of the model, and also the reality (please have a look on official measurements reports of TÜV or others if you avail). - The muGamma correction is a little "ad hoc" correction just for matching the muPmpp of the model to the specified value. In you case a discrepance of 0.04% to -0.07% is really very low. Personally, I am really surprised that the one-diode model behaves with such an accuracy in this case !!! Link to comment Share on other sites More sharing options...

marianne.hartung Posted January 17, 2013 Author Share Posted January 17, 2013 Thanks for your answer. Unfortunately, I think that the observed effect is not a rounding error but a problem with the "gamma temperature correction" tool. It works fine, if reference conditions are at STC. Otherwise problems occur. The example below should explain this. I am using the same PAN File as I have explained in my previous post. It is based on the "50 Wp 15 V, Si-poly, CS 50, Centennial Solar, Photon Mag. 2009" PAN File, but the reference conditions are 800 W/m² and 45°C. The inputs for Imp, Isc, Vmp, Voc and muIsc have been adjusted accordingly (cf. to my previous post.) I try different values for the temperature coefficient at STC in the "Definition of a PV module > Model parameters > Temper. coeff" sheet. This is what I get: specified Tc ------> resulting gamma ------> resulting Tc (Internal model result)--------------------------------------------------------------------------------------------------0.43 %/°C -------> -0.04%/°C -------> -0.44%/°C-0.44 %/°C -------> -0.07%/°C -------> -0.45%/°C-0.45 %/°C -------> -0.09%/°C -------> -0.46%/°C-0.46 %/°C -------> -0.11%/°C -------> -0.47%/°C-0.47 %/°C -------> -0.14%/°C -------> -0.48%/°C-0.48 %/°C -------> -0.16%/°C -------> -0.50%/°CThe first column of the table is the temperature coefficient at STC that I specify in the "Definition of a PV module > Model parameters > Temper. coeff" sheet. The second column of the table is the resulting "Gamma temp. coeff" from the same sheet. The third column is the temperature coefficient from "Definition of a PV module > Basic data > Internal model result" tool at 1000 W/m² and 25°C.I understand that the temperature coefficient is not constant with temperature. However, in the example above both temperature coefficients are at STC. In the "Definition of a PV module > Model parameters > Temper. coeff" sheet one has to specify the temperature coefficient at STC. In the "Definition of a PV module > Basic data > Internal model result" tool I selected 1000 W/m² and 25°C. Link to comment Share on other sites More sharing options...

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