How to adjust the design temperatures ?

[André Mermoud]

The design of the PV array (namely the number of modules in series) uses a set of design temperatures, used at the design time only for parameter suggestions or system configuration checks.

These temperatures may be specified for your project (button "Albedo-Settings"), and their default value for any new project may be specified in the Hidden parameters, topic "System design parameters".

- TMin: Lower temperature for Absolute voltage limit: The Voc(Tmin) requirement corresponds to a safety requirement:

The array voltage Voc should never overcome, in any case:

- neither the inverter's VabsMax (absolute input voltage, corresponding to the input electronics circuit voltage limit),

- nor the absolute array maximum voltage admitted for your PV modules (usually 1000 or 1500V).

Therefore the reference temperature for this evaluation is the lowest temperature even observed on this site.

- In middle-Europe climate (and not in altitude), a usual best practice is to choose -10°C. But this should be decreased for high altitude or northern regions.

- In other situations, you should take the lower temperature ever observed during the day (eventually with an irradiance superior to 10 W/m2) for this site.

Choosing 1000 W/m2 means that in worst case, in winter the sun may suddenly appear on the array (cloud), and in this case the cell's temperature may be the ambient temperature. Remember that the Voc is very slightly dependent on the irradiance.

These conditions are a common practice, adopted by everybody. They are specified in the norm IEC TS 62738 (2018), paragraph 7.2.1.

Now if you want to overcome these constraints (which is really not recommended), you can:

- modify the reference low temperature in the Project's parameters (button "Project Settings"),

- modify the muVoc coefficient if you don't believe the PVsyst's model value (in the PV module definition, page "Additional data > Secondary parameters" ).

- artificially increase the maximum voltage limit in the Inverter's and/or PV module's definitions.

NB: These modifications will alter the warranty of your PV system. If you do that this will be at your own risks.

- ToperMin and TOperMax: the usual operating conditions of your array, during winter and summer (cell temperature).

ToperMin will be used for the maximum number of modules in series, in order to stay below the VmppMax input value of the inverter.

ToperMax will be used for the minimum number of modules in series, in order to stay above the VmppMin input value of the inverter.

These values are not critical, and may usually be let to their default values. Slightly overcoming the voltage limits doesn't induce important losses (in case of doubtful sizing, you will observe an "Inverter loss over nominal voltage" or "Inverter loss due to voltage threshold" in the loss diagram of the simulation).

- TOper: Usual operating (cell) temperature under 1000 W/m2, is an intermediate value, only used for the display of a usual "operating power" in the sizing dialog (and the report).

In the version 6, these definitions are part of the parameters of your project, button "Albedo and Settings".

They may eventually be modified according to your climate.

The default values (initializing value for each new project) may be redefined in the Hidden Parameters, topic "System design parameters".

These parameters are used for design only. They are not involved in the simulation in any way.