Design's Temperature Parameters

[Nuno.11]

Good afternoon PVsyst team,

My name is Nuno and I work in a Renewable Energy company as a PV Design Engineer and our team has some doubts that we would like to clarify, but we feel that we need your input, since your team is the one that developed the software and knows everything in detail.

The main doubt that our team struggling with is regarding the Design's Temperature Parameters. I am attaching to this post 2 PDF files which contains the weather data measured by a weather station near the project location (9 km far away, approximately). The Temperature_Full_Days.pdf file shows the temperature measured during the 24 hours of each day considered and the Temperature_Sunny_Hours.pdf file shows the temperature measured during the sunny hours of each day considered.

As you can see in the Temperature_Sunny_Hours.pdf file, in 1800 hours of sun (from 8 a.m. until 5 p.m. - during the months of December 2021, January 2022, February 2022, December 2022, January 2023 and February 2023), we got 105 hours where the hourly average temperature was lower than -20 ºC and 20 hours where the hourly average temperature was lower than -25 ºC.

Our question is:

Shall we consider the Lower Temperature for Absolute Voltage Limit as -25 ºC? Shall we consider it as the minimum temperature of the sunny hours of these months (-28.5 ºC)? Or shall we consider it as the minimum temperature of all hours of these months (-29.4 ºC)?

Also, could you please tell us what would be the implications and consequences if we have considered a higher temperature than the one we should consider?

If you need more information, like the PVsyst Project file and all the weather data that we have, just let me know.

Looking forward for your answer and thank you for your attention and availability.

[André Mermoud]

The design temperature for defining the max. Voc value (to be compared to the VAbsMax of the inverter and the PV module) should be the minimum temperature measured during the day.

This is a safety condition, for avoiding overvoltages damages at the inverter input. This is specified in the norm IEC TS 62738 (2018), paragraph 7.2.1.

Now for such low temperatures, the one-diode model doesn't work well. For many modern modules, the temperature behaviour is not quite correct below -10°C. In this case you should consider a linear increase of the Voc value as function of the temperature instead of the one-diode model.

You can do that by:

- defining a customized muVoc value for your PV module  (page "Additional data > Secondary parameters")

- in the "Project's settings", specify that your design should use this value  (open "Project's settings > Design conditions", and choose "muVoc value: from specification".

[Nuno.11]

Good afternoon André,

Thank you for the reply.

Just one question. Regarding what you wrote, our team should consider the minimum temperature during the sunny hours which is -28.5 ºC, correct?

Once more, thank you for your attention and patience André

[André Mermoud]

Yes, this is what I said.

[Nuno.11]

Good morning André,

Thank you for your reply and confirmation. All the information that you gave us it will be very helpful.

Once more, thank you for your attention and patience.