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# Bifacial systems results

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# Bifacial systems results

The detailed results of the bifacial model are available on the Loss diagram.

Here is an example, with a description of all output variables involved:

In the Report editor, you can also export the values into Excel (menu "Export > Loss diagram values), which gives some explanations about how to calculate some values:

Detailed variables description:

 GlobGnd Global incident on the ground.
 This is the total irradiance reaching the ground area below the installation (beam and diffuse).
 This irradiance [W/m2] is referred to the reflecting reference area (in 2D models: proportional to the pitch).
 ReflLss Ground reflection loss (albedo)
 This is the loss of irradiance due to the reflection (1 - Albedo), referred to the ground reference area.
 BkVFlss View factor for rear side
 Each point of the ground is supposed to receive an irradiance (luminous power) specific to its position on the ground, and the sun's position.
 After reflection, this point will re-emit the same power in all directions  (isotropic hypothesis, i.e., Lambertian distribution), according to the albedo factor.
 Now a part of this power will be intercepted by the rear side of the collectors, the rest is lost (sky). The view factor is the fraction of this interception for each given point.
 The total power received by the rear side is the sum of all ground points contributions. This power will result in an irradiance [W/m²], which is now normalised to the m² of collector area.
 Therefore when expressed as irradiance (not Power), this view factor should be multiplied by the Ground area and divided by the Collector area  (i.e., 1/GCR).
 DifSBak Sky diffuse on the rear side
 This is the contribution of the diffuse irradiance, coming directly from the sky.
 BeamBak Beam effective on the rear side
 This is the contribution of the eventual beam coming directly from the sun:
 - with sheds, possible in the morning and evening when the sun passes behind the East or West.
 - with vertical East-West rows, when the sun is opposite to the front side,
 - with tracking systems, never.
 BackShd Shading loss on rear side
 Due to the mechanical structures (corresponding to the specified  "Structure shading factor").
 GlobBak Global irradiance on rear side
 Is the sum of all these contributions.
 This value is mentioned in [kWh/m²], and as a percentage of the GlobEff value.
 EArrNom Array Nominal energy at STC efficiency
 The reference energy of the array is defined as the sum of:
 -  the GlobEff value,  multiplied by the PV modules area and the STC efficiency,
 -  the GlobBak value, multiplied by the PV modules area,  the STC efficiency and the bifaciality factor.

There are 2 other contributions linked to the bifacial model: