Shading losses on Output file

[Fredy]

Hello

We are having a problem with the production in a plant that is already working, we are having half the production that PVsyst gave us

I found this values referent to shadings in the output file:

 

the Near shading Animation corresponding to this table is the image bellow (it’s just an part of the plant + shading factors and graph):

 

So could you clarify the meaning of this values on the output file?

-Global correction for shading: Irradiation reaching the modules counting with the shadings?? If it is correct shouldn't it be lower for example at 9:00h globInc=19.277 GlobShd=18.504 it is just 0.77w/m2 difference and on the near shading animation I see almost all the plant shaded at 21-12 _ 9:15h

-Near Shading loss (w/m2): I don’t understand this one. Is it the quantity of irradiance loss due to shading? Why I have more losses at 12:00h than at 9:00h?

-Near shading factor on global: Globshd / GlobInc OK. This should be the % of irradiance loss due to shading but because of the previews parameters we are having more losses at 12:00 than at 9:00...

Is PVsyst taking this shading losses correctly it seems

Is there any other parameter i can use to see the shading loss % ?

Thanks in advance for your help

[Fredy]

I was analysing the output file tables and for what i understand PVsyst is taking the shading loss constant for all the hours

 

 

So PVsyst just uses the Near shading Table and shading factors to calculate 1 final Shading loss that is used constant in every hour?

Shouldn't it use the shading factores that it calculates in the near shading table to get the values for GlobEff / EARRay etc... correctly for every hour?

[Fredy]

Hello I’m sorry for the spam

I found that for Horizontal Beam there are some values missing or low values a lot actually,

Maybe this could be the reason why I’m getting this

For this test I’m using another Meteo file from PVGIS On the first Post I was getting BeamHor = 0 in every cell for 21-December, but now even with this one from PVGIS there are some missing values.

In the images bellow the red/green cells corresponds to the acceptable / unacceptable values for BeamHor

Blue Cells were calculated: (ShdLoss / GlobInc.) to have a perception of the loss %

In this table we can see that there are some missing values and low values that doesn't make sense more losses at the mid of the day then at morning

I found this one acceptable at least make more sense than the other two

This one seems good too more losses at morning/afternoon and less on mid-day

 

It was harder to find correct values then wrong / missing values.

1- Could you see if this is a bug from the program it fails to generate some values or something?

2- The program calculates the shadows for every hour with the corresponding shading factor but it needs the beam Irradiation right?

Thank you in advance for your support

[André Mermoud]

Many questions.

The shading losses in PVsyst are of several kinds:

- Loss on the beam component: the shading factor is the ratio of the shaded area to the total sensitive area. This may be pre-calculated in a table (as function of the sun's orientation) for a quick use by interpolation during the simulation. This may also be calculated at each simulation step (slower process).

- Loss on the diffuse component: this is based on the hypothesis of an isotropic diffuse, and results from an integral of the shading factor for rays comming from all directions "seen" by the collector plane

(orange slice of the heavens between collector plane and horizontal). This doesn't depend on the sun's position, and is therefore constant over the year.

- Loss on the albedo component: same idea than for the diffuse: the integral is performed on the "orange slice" between the horizontal plane and the prolongation of the plane undergroud. The factor is shaded for parts below obstacles on the ground.

There are also the shading factor "according to module strings" and "according to module layout" for the electrical mismatch effect, but this is another question.

Now when you have a completely covered day (i.e. without any beam contribution), the shading loss in indeed determined according to the constant loss factor on the diffuse, what you observe in your results.

In the results, you can get the 3 contributions (in hourly or monthly values): ShdBLss, ShdDLss, ShdALss, ie. shading losses on beam, Diffuse and Albedo respectively.

And the corresponding shading factors (0 = full shading, 1 = no shading).

[Fredy]

Thank you for your help,

Ok so PVsyst considers some days covered cloudy?

Normally I see monthly values when importing from external Meteo data

This hourly tables are interpolated by PVsyst when we do the synthetic hourly data generation?

It is a probability calculation?

Sometimes 0 for beam irradiance and sometimes x% for Beam irradiance?

Where can I find this?

Thank you for your support in advance

[André Mermoud]

The simulation of PVsyst works on an hourly basis: one calculation for each hour, according to the meteo data for this hour (Global and diffuse irradiances, temperature).

Now when meteo data are only available as Monthly values, PVsyst has to generate a synthetic hourly data file (random distribution) for working.

See our FAQ What are Synthetic Hourly Data ?