# Calculation of TArray

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Hi all,

I want to know how PVSyst calculates TArray (for monofacial and bifacial modules)

As I can see in: https://www.pvsyst.com/help/thermal_loss.htm

0) This is the formula that uses PVSyst. Is it right?

1) Tcell is TArray?

2) U = to the value introduced by the user (for instance U=29 W/m2K) , or U is calculated (ignoring the fixed value introduced by the user)?

3) Alpha is always 0.9?

4) Ginc: Which variable is?

Ginc = GlobInc ?

Ginc =GlobEff ?

Ginc = (GlobInc + GlobBak) ?

Ginc = (GlobInc + BifacialityFactor * GlobBak) ?

5) Effic is always 10%?

I enclose different calculations I have made and the differences between calculations

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0) right
1) Yes, in fact we iterate the formula twice, because the efficiency depends on the temperature.
2) U = Uc + Uv * WindVelocity, and the values are kept as entered by the user.
3) usually, but it may be different (it is defined in the module, you can find it under "Additional data" / "Secondary parameters"
4) GlobEff
5) efficiency is the module PV conversion efficiency, not jut 10%. See point 1, we start with the efficiency at ambient temperature, and then iterate the formula.