Mismatch for back irradiance

[Choohuey Mei]

Hi, I am trying to calculate the value for "mismatch for back irradiance" based on the formula and explanation as following:

https://www.pvsyst.com/help/bifacial_results.htm

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"MismBak Mismatch for back irradiance

This is the result of the Mismatch parameter specified by the user (see Bifacial Procedure)

At this stage of the Array losses, on the results diagram this is referred as percntage of the full system energy.

As an example, if you have specified a loss of 10% (of the bi-facial contribution), and you have a bi-facial contribution of 15% of GlobEff, this will be 10% of GlobBakEn / (GlobBakEn + GlobEff).

NB: Here the GlobBakEn is GlobBak * Bifaciality factor"

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Lets say

My PVsyst report shown the value of:

Input for mismatch for back irradiance loss: 10%

GlobBak: 38 kWh/m2

GlobEff: 1742 kWh/m2

Bifaciality factor: 0.7

Based on the paragraph:

GlobBakEn = GlobBak x Bifaciality factor = 38 x 0.7 = 26.6 kWh/m2

"Mismatch for back irradiance" as show in the loss diagram over the whole year = 10% of GlobBakEn / (GlobBakEn + GlobEff)

= 10% of [26.6/ (26.6+1742)]

=0.1504%

I cannot get the value as per the loss diagram, as my PVsyst loss diagram show the value is 0.21%

I only get it with further divide by 0.7

= 10% of [26.6/ (26.6+1742)] /0.7

=0.2149%

Appreciate for your advice.