Jump to content

IAM (incidence angle modifier)


Recommended Posts


I have noticed modules have vastly different IAM (incidence angle modifier) values. Ranging from 95 to 99 to 99,9 to 100.

This has a fairly significant impact on the yield. How reliable are the IAM values provided by the manufactures and what level of auditing is done? These values are obviously not shown on the module datasheet and it seems suspicious that there is such a big range in values provided. 

I see for example that PVSyst requires a third party report from manufacturers if they claim non-standard IAM values for their modules.

Does PVSol team also apply this kind of due diligence or are manufacturers free to provide whatever database entries they chose?  

Any insight in this regard would be greatly appreciated!


Link to comment
Share on other sites

Hi Josh,

the module data entered by the manufacturers is only checked against min/max values, we do not require a third party report. The manufacturers are responsible for the data they enter. But if we encounter irregularities, we usually contact them to clarify the issue.

The model we use to calculate the reflexion losses is the one from AHSRAE:


Hope that helps, kind regards,


Link to comment
Share on other sites

  • 8 months later...


I share the exact same concern of Josh. If the IAM parameter isn't stated in datasheet and isn't subject to third pary auditing, manufacturers tend to give the highest value possible to gain a "virtual" competitive advantage. From what I have observed from your database, when manufacturers add/update their modules, they either increase slightly their IAM values, or aren't able to do so because they have reached 100%.

In that sense, I have some questions regarding the assessment of this parameter in your software:

  • What are exactly the min/max values that you consider for this parameter (is 100% the max value?)
  • What value(s) do you consider for the ASHRAE IAM model's parameter? And do you consider that this parameter depends on the module manufacturing (e.g.: single glazed, AR coating,...)
  • Have you consider using other models to define the IAM value?
  • Do you require manufacters to deliver results from the IAM measurements, and does these measurement procedures follow the IEC 61853-2 directive?

Can you please help me clarify this matter?

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Unfortunately, your content contains terms that we do not allow. Please edit your content to remove the highlighted words below.
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...