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PostPosted: Fri Jan 24, 2014 6:16 pm 
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Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1680
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 should never overcome the VabsMax (absolute input voltage of the inverter, corresponding to the input electronics circuit voltage limit), in any case.
Therefore the reference temperature for this evaluation is the lowest temperature even observed on this site, and under 1000 W/m2.
- In middle-Europe climate (and not in altitude), the usual best practice is to choose -10°C.
- 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.
These choices are a universal common practice, adopted by everyone (not only PVsyst users).
However I don't know whether they are mentioned in an IEC norm about system sizing.

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 value (in the PV module definition, page "Additional data > Secondary parameters" ).

- 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.

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