How to adjust the lowest temperature range for the absolute voltage limit?

[Edwin Tellez]

Hi everyone!

Currently, I am trying to carry out a simulation for a photovoltaic project where the customer requires strings of 40 photovoltaic modules of the RISEN brand, model RSM110-8-550BMDG, which has a Voc of 38.32V. When the total number of photovoltaic modules in series is multiplied by the Voc, it gives a value greater than 1500V (more exactly 1532.80V). This result has been reported to the customer, who assures that he has carried out an analysis with his own software (he does not indicate which software he refers to), where at an average temperature of 25°C he obtains a total String voltage of less than 1500V. The place where the photovoltaic project is intended to be carried out has a minimum temperature of 23°C according to the meteorological database (TMY). The client also reports that the analyzes are carried out according to the recommendations indicated by the IEC 60891, IEC 62738, IEC 62548 standards, as well as the formulas shown below:

(1)

(2)

(3)

For a range of irradiances between 100W/m2 and 1500W/m2, the following results are obtained:

It can be observed that at an irradiance of 700 W/m2, the maximum voltage obtained at 21.3°C is 1407.09V, which is below the maximum DC voltage at the inverter input (1500V).

But with PVSyst it is not possible to configure a string of 40 modules since it is not allowed as the Voc allowed by the inverter is exceeded:

 

I have tried to adjust the minimum temperature for the absolute voltage limit, but it does not allow adjusting to a temperature higher than 30°C in such a way that it allows reducing the Voc below 1500V, and thus achieving the continuation of the photovoltaic system simulation:

Is it possible to adjust the minimum temperature range for the absolute voltage limit?

What other option or parameter can I adjust to be able to perform the simulation?

Thank you very much for your attention and support.

[Michele Oliosi]

10 hours ago, Edwin Tellez said:

The place where the photovoltaic project is intended to be carried out has a minimum temperature of 23°C according to the meteorological database (TMY).

As a side note, a TMY is not the good place to look for a minimum temperature. You should look for a minimum temperature over many years of time series data. The TMY is a snapshot with a biased take, aimed at representing an average year.

Currently, there is no way to change the maximum limit of 30 °C. The only other way is to modify the OND, and to manually set up the absolute maximum voltage to a higher value. We do not recommend it, but it has been done by some users.

[Edwin Tellez]

Hi Michele!

Thank you so much for your feedback.

I'm going to search others time series data and I'll considerate modify the OND, although it is not technically recommended.

kind regards.

[dtarin]

I do not think there is anywhere (where someone would build solar) that has a low temperature of 30 degrees C, and I wouldn't recommend forcing the design to accommodate what the customer thinks is correct. As Michele noted, you are not concerned with average site temperature, but the lowest temperature at which there may be sufficient irradiance. If you design to 30 degrees C, your inverters will most likely have frequent start-up issues and the warranty of all components will be in jeopardy. That is not a 1,500V design. 

[Edwin Tellez]

The client says that through its own software it can configure strings of 40 modules RISEN brand modules RSM110-8-550BMDG, but in PVSyst it does not allow this, but rather a maximum of 38 modules in series with a minimum temperature of 20°C. The client also says that they consider a minimum temperature during peak production hours of 20°C. Is it possible to configure strings of 40 modules in PVSyst through RISEN brand modules model RSM110-8-550BMDG?

The installation location is at the following coordinates: #Latitude: 10.615 / #Longitude: -74.81

I greatly appreciate your support.

[Michele Oliosi]

Other than the solution of changing the inverter limits and the minimum temperature, there is no other way. Your client should explain the calculation for Voc at 20°C that explains such an aggressive string sizing. In PVsyst you can check the module Voc at different conditions in the module window: