Array Thermal Losses - Summary

PV modules' nominal performance is specified at \(25 ~\mathrm{°C}\), but in operation the PV array typically reaches much higher temperatures, which leads to thermal losses (about \(-0.2\) to \(-0.4 ~\% / \mathrm{°C}\)). Therefore, this discrepancy between the STC temperature and the real operating temperature translates into a power loss when the PV array operates above \(25 ~\mathrm{°C}\).

In PVsyst, two layers of thermal models are used:

• First, a thermal balance model outputs the steady-state temperature, represented by the PVsyst variable TArrSS. This model requires a set of heat transfer coefficients, commonly called U-values, which must be fitted to real system data.

• Second, a thermal inertia model uses the previously calculated steady-state temperatures to compute the actual transient temperature, represented by the PVsyst variable TArray.

The user can modify the heat transfer coefficients and the mass of the module (affecting the thermal inertia) in the detailed losses and .PAN file menus, respectively.

Note that during the simulation, each subarray (and each orientation in the case of mixed orientations) has its own steady-state and transient temperatures in order to compute PV production correctly. However, in the output results, the variables TArrSS and TArray represent the corresponding averages over all subarrays and orientations.

Alternatively, it is also possible to import a measured PV array temperature (TArrMes) for the main array into PVsyst using the custom weather import. This allows you to run the PVsyst simulation directly with the provided temperature, rather than computing it from PVsyst models.