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How is incidence angle modifier calculated for diffuse component


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I'm assisting in a university research related to incidence angle modifiers and dye-sensitized solar cells. We're deciding whether or not to use PVsyst in a simulation related to the research.

My question is how is the IAM calculated for the different radiation components (Dp, Bp, Ap)? In the case of isotropic diffuse radiation, I think the effect of the IAM should be included in the same integral with which the Dp component is calculated. Or is the IAM factor calculated afterwards? I didn't find a mention in the help -file about this. I did found this:


Incident "effective" energy calculation

- Reading one hour data on the Meteo file (Horizontal global irradiation, temperature, eventually

diffuse irradiation and wind velocity).

- If not available, computes diffuse irradiation with the Liu-Jordan correlation model,

- If necessary, applies the horizon correction on the beam component,

=> defined variables at this stage: GlobHor, DiffHor, BeamHor, T Amb, WindVel .

- performs the transposition (global, diffuse, albedo irradiations) in the collector plane, using either

Hay or Perez model according to user's preference.

This is done using solar angles at the middle of the time interval, calculated from project's site (not

the site of the meteo file).

With explicitely given meteo files (TMY or own measurements), this could give not very reliable

results at early morning or evening, if the time properties of the meteo file are not properly defined (legal or

sun time), or if latitudes of the two sites is very different.

=> defined variables at this stage: GlobInc, BeamInc, DiffInc, DiffSInc, AlbInc ,

- applies the shading factor (if near shadings defined) on the beam component,

- applies the IAM factor on the beam component.

=> defined variables at this stage: GlobIAM, GlobShd, GlobEff, DiffEff ,

This leads to the so-called "Effective incident energy", i.e. the irradiation effectively reaching the PV cell



The bolded part gave me the impression that the IAM doesn't affect the diffuse component at all.

I'd like to confirm this so I'll know if we can use PVsyst in the research.

Thank you for your efforts!



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The effect of the IAM on the diffuse component is calculated assuming an isotropic diffuse distribution.

It results of the integral of the IAM loss over all directions of the sky "seen" by the PV module.

As this value is independent of the sun's position, it is constant over the year, and applied to the diffuse component at each step of the simulation.

The same stands for the Albedo component.

NB: This integral is indeed performed simultaneously with the shading factors if horizon or near shadings are defined.

Sorry, I discover that this part of the help is incomplete and rather old: I have updated it for the next version 6.26

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Note also, that if you are interested specifically in the IAM, PVsyst can generate for you a lot of detailed intermediate results such as:

- IAM factor on global

- IAM factor on beam component

- IAM factor on diffuse component

- IAM factor on albedo component

- ...

and many more, that allow you to study in detail the effect of the IAM on the simulation results.

In the program you need to click on 'Output File' in the 'Simulation' Dialog, and then choose the variables that you would like to have in the output.

See also the online help under 'Project Design -> Simulation -> Export ASCII File'

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  • 4 weeks later...

Hello again!

I am now trying to replicate the results of another research with PVsyst. I've created a custom defined profile for the IAM losses in the 'detailed losses' part with the help of a reference article.

The reference article itself is: Martín, N., & Ruiz, J. M. (2005). Annual angular reflection losses in PV modules. Progress in Photovoltaics: Research and Applications, 13(1), 75-84.

I can send a pdf to an email unless you have access to the article. The model they used is described in the beginning of the article.

Now, the results I'm getting with PVsyst are still a little off from the article's values of annual angular losses. I've tried adjusting some of the settings in PVsyst but none of them seemed to have any effect on IAM losses, apart from the IAM curve itself and albedo settings that were kept the same as in the article. (Choosing between Perez and Hay model had some effect, but the difference in IAM losses was only about 0,3 %).

Does the model used by PVsyst differ so much of the article's model?

Or is there a significant difference between the meteo data? The article used meteonorm data 5.0 whereas PVsyst uses 6.1.

Or is there something else I haven't thought of?

I'd appreciate any insight! Thank you!


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I don't know the model used in this article.

In PVsyst, the IAM calculation may be dependent on the meteo data as you pointed out (especially the diffuse component or the transposition model used), an on the plane orientation.

I have done a little correction on the calculation for the albedo some months ago (effect less than 0.1 or 0.2% if I remember well).

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