# String Voltage Calculation

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I would like to understand the string voltage calculation for minimum, maximum and arbitrary temperature values. As per my understanding following are the calculations:

Vmin = {(Tmax – 25) X ∆Vmp* X Vmp + Vmp} X No. of Modules

Tmax is Day Maximum Module Temperature

*∆Pmp shall be taken if ∆Vmp is not provided by manufacturer

Vmax = {(Tmin – 25) X ∆Voc X Voc + Voc} X No. of Modules

Tmin is Day Minimum Module Temperature

VNOCT = {(TNOCT – 25) X ∆Vmp* X Vmp + Vmp} X No. of Modules

TNOCT is NOCT Temperature provided by manufacturer

*∆Pmp shall be taken if ∆Vmp is not provided by manufacturer

However, we have also found some references which suggest following for minimum string voltage:

Vmin = {(Tmax – 25) X ∆Vmp* X Voc + Voc} X No. of Modules

Tmax is Day Maximum Module Temperature

*∆Pmp shall be taken if ∆Vmp is not provided by manufacturer

There are certain projects whose feasibility is at stake due to this confusion.

Kindly suggest.

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You can calculates these values in this approximate way if you want.

However PVsyst doesn't need these VMin and VMax values during the simulation, it calculates the effective Vmpp at each operating hour from the one-diode model.

It only needs these values (as well as the Voc(TMin) at the desigh time, for the determination of the minimum and maximum numbers of PV modules in series.

Please see the help "Project design > Grid-connected system definition > Array voltage sizing" for a complete explanation of this sizing process and the corresponding tool.

And our FAQ How to adjust the design temperature ?