Number of sheds in "Unlimited sheds" — does it affect results?

[RAOUANE LAILA]

Dear PVsyst team,

In the Orientation → Unlimited sheds section, it's mentioned that the "Number of sheds" is only for visualization and does not affect simulation results.

However, I noticed that changing this number (e.g. from 5 to 12) slightly alters the energy yield and PR, even when mutual shading is disabled and all other parameters (pitch, tilt, GCR, etc.) stay the same.

Could you please clarify:

1. How should we choose or calculate the number of sheds?

2. Why does it impact the results if it's only for display?

3. Could internal parameters (like edge effects or area estimation) be influenced?

Thanks in advance for your help.

Best regards,
Raouane Laila

[Michele Oliosi]

Hi !

Which version are you using? I am asking this because in the current version this is not stated, as far as I know. 

The unlimited orientations do always include mutual shadings. The shadings calculation is inherent and is not related to choices in the "Near shadings" window.

The number of rows (with the frenchism "sheds") is actually quite important for the evaluation of mutual shadings: it does affect simulation results.

[RAOUANE LAILA]

I am currently working with PVsyst version 7.4.

Thank you for your response.

In my case, I only have the total number of strings and the number of modules in series per string. Could you please guide me on how to calculate or estimate the appropriate number of sheds from this information?

Is there a rule of thumb or a formula to follow based on the electrical layout (e.g. 24 modules per string, 3058 strings in total)?
I would like to make sure that the "Number of sheds" I enter corresponds realistically to the physical arrangement of the system in the field.

Best regards,
Laila Raouane

[Michele Oliosi]

It depends on the layout of the strings in the field.

We don't have a rule of thumb, but you could do something along these lines: you can make some simple assumptions concerning your field.

For example, if your trackers are 2P (two in portrait), then you could assume that there are two strings per tracker, i.e. 1529 strings total.

Then you could also assume that the trackers are roughly arranged in a square terrain, with GCR 0.4. And that modules are 1x2 m^2.

Let's say x is the number of trackers on a single line along the axis and y is the number of rows. Roughly, y * 2 (# modules in table height) * 2m (module height) / 0.4 (GCR) = 24 (# modules in table length) * x * 1m (module width), i.e., y = 2.4 x.

The total number of trackers is 1529 = y * x = 2.4 * x^2. Solving, that you get roughly x ~ 25 and y ~ 60. So 60 rows should be roughly it.

Note that above 10-20 rows, the impact of the number of rows becomes quite small, so for systems of this size the exact values are not important at all.

[RAOUANE LAILA]

Thank you Sir. Now it's clear. I’ll apply this logic to my system.

[RAOUANE LAILA]

Hello,

I am running simulations in PVsyst for both monofacial and bifacial modules using the unlimited sheds configuration to avoid performing a shading scene simulation.

I noticed that even when I keep the same spacing between sheds and only change the number of sheds in the layout, the simulation results (energy production and PR) still vary.
I had assumed that in unlimited sheds mode, with shading simulation disabled, the number of sheds would not affect the results since the geometry is considered infinite in the transverse direction.

I would like to better understand the logic and assumptions PVsyst uses regarding the number of sheds parameter, and why it impacts the results for both monofacial and bifacial modules.

Thank you in advance for your help and clarifications.

Best regards,

Raouane Laila

[Linda Thoren]

Hi,

The idea behind the unlimited sheds field type, is to allow for simulation of the shadings without the complexity of the 3D scene. Thus you are always simulating the mutual shading between the rows in a 2D representation (compared to the 3D scene). One simplification with this 2D representation is that the edge effect is neglected, that the rows are unlimited long. The number of sheds are important to define since the first and last row does not have the same shadings as the rest of the rows. Thus if you have 5 rows, 4 of the rows experience mutual shadings. If you have 500 rows, 499 rows will experience mutual shadings and thus this will impact the simulation results. 

Note that the unlimited sheds always include mutual shadings. To run a simulation completely without shadings, you should define fixed tilted planes and not define a 3D scene (though you can then define a bifacial project since the pitch and table size are needed for the bifacial calculation).

You can read more about the unlimited sheds in the following help page:
https://www.pvsyst.com/help/glossary/3d-editor/shed.html?h=unlimited+sheds