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IAM for normal incidences


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Dear all,

I am surprised to see that IAM equals to 100 % for normal irradiance when using ASHRAE modelling. Indeed, the enclosed First Solar document states an IAM close to 92 %. Do you think it is particular to First Solar glass?

Best Regards

Christophe Vernay


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  • 2 weeks later...

This is just the definition of the IAM: "Incidence angle Modifier": it is the deviation of the reflexion loss whith the incidence angle, with respect to the normal.

The curve of First Solar represents the total irradiance reflexion losses. But in the usual definition of the IAM, the loss under normal incidence is fully included in the STC measurement / definition.

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