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PV glass cover transmittance


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The specifications of the module at STC (or any other irradiance level), includes the glass cover, so it is not necessary to add it separately.

PVsyst assumes that the values from the module specifications are valid for an incidence angle of 90°. It then applies the Incidence Angle Modifirer (IAM) to account for the different incidence angles along the day and seasons.

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Hi Amir,

the IAM is just a factor that is applied according to the incident angle. The details are given in the online help under 'Project Design -> Array and system losses -> Array incidence loss (IAM)'. You can find this page also on the web.

The ASHRAE model used in PVsyst is a simplification, but should give good results in most cases.

The transmittance of the glass cover is only relevant for multiple reflections, which contribute little to the overall loss estimation. The non-perfect transmittance is neglected by the model. In the attached picture you can see as an example the comparison between the ASHRAE model, a calculation with double reflection using Fresnel's law and the measurement from the manufacturer.

If a better approximation than ASHRAE is known for your system, you can define a customized IAM profile in the dialog 'Detailed Losses', tab 'IAM losses'.

The definition of the IAM profile can also be provided in the PV module definition file (PAN file). In this case the 'IAM losses' tab will display a checkbox allowing to choose the definition from the PV module file.

Best regards,



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