Horizon (far shading) defined but not taken into account

[unilhexio]

Hi,

I have just defined the horizon line drawing for a project as shown:

http://fotos.subefotos.com/b8e7869e471377bdb06b4f79cb8f51f9o.jpg

But it does not appear on the final report.

Even, as you can see, the 'Horizon' option appears turned off:

http://fotos.subefotos.com/b87276a6607ef0f1858f62e55ea1e262o.jpg

May it be that the horizon is too low to be taken into account for the simulation?

[André Mermoud]

In PVsyst, an horizon line below 2° is not taken into account.

By the way this would not be significant, especially in sub-tropical climates.

[Soldnerkugel]

It also depends in which time intervals you compute your yield simulation... E.g. 2 degrees should be only a few minutes after sunrise or before sunset at any location on the globe. So imagine using an intervall of 1 hour PVsyst (most probably) will use not the "full" hour but the middle between two fulls hours (30')... So 2 degrees is not relevant, even using an interval of 1/2 hour dor your computation will not have any impact at nearly all locations on the globe on far shadings.

I thin questions like this one only arise because most user of pv simulation software products have no idea or only a reduced knowledege about e.g. Sunpathes, climate databeses etc. To me this is one important field which still needs lot of improvement within PV. How shall one know how to properly design a pv plant without knowing how the behaviour of the plant is modelled? The most advanced software is only as good as its operator.

[unilhexio]

I thin questions like this one only arise because most user of pv simulation software products have no idea or only a reduced knowledege about e.g. Sunpathes, climate databeses etc. To me this is one important field which still needs lot of improvement within PV. How shall one know how to properly design a pv plant without knowing how the behaviour of the plant is modelled? The most advanced software is only as good as its operator.

 

I do not mean that the impact of a very low horizon is significative. My question is more related with the reason of why is this horizon not mentioned in PVsyst report. Even 0% PV losses are mentioned in the final report...

But, of course, may be I have no idea...

[André Mermoud]

For the horizon shading calculation, PVsyst analyses the time at which the sun crosses the horizon line. And applies the shading effect (i.e. suppression of the beam component) only on the concerned hour fraction. Therefore the result is not directly related to the hourly step.

[rip_xellos]

Hello,

I didn't want to create a new post for this small question. Is it acceptable to generate horizon line diagram using an image off google? I used this image in Meteonorm 7 to generate a *.hor file that i can input in PVsyst.

This is what i generated...

 

I cannot make a site visit and so I'm forced to use a google image. Also in PVsyst help it says 'Synthetic model cannot know the horizon line and will create dummy hourly values below the horizon' What does this mean?

I'm using synthetic hourly data, I do not have 'original' monthly values to generate hourly files with horizon correction.

Should I continue with my file or do the simulations with a clear horizon?

[André Mermoud]

Nothing prevents you to use a google image for the definition of the horizon, if you can define the "horizontal line" (here the lake) on the photography.

Without this reference it would be more difficult.

Now if you avail of ground measured data, they already include the horizon effect.

If these are hourly data, there is no real problem: you will not take an horizon line into account in the simulation.

But if these are monthly values, the hourly data should be created using the synthetic generation, and this model "ignores" the horizon line.

Please see our FAQ How to deal with meteo data which include horizon loss ?