Array Partitioning with Sheds Fields

[Rachel Hamilton]

Hi PVsyst forum,

I was wondering what would be the best way to model a system with very irregular table shapes. The system I am trying to model is much larger than the 1MW recommended limit for using the module layout definition. The following diagram shows a small section of the array:

I know I can use the zone option with exclusion areas and PVsyst will fill in the rest, however in this case I will need to define the table unit as a single module (or maybe 2 modules, depending on the zone) to make sure that the area is filled accurately. This creates a problem for partitioning the strings since PVsyst forces you to define the table unit as a minimum of a single rectangle string partition; it does not let you define a single module as 1/30 of a string (even though it is). 

I see a similar issue with using array tables/shed fields in various shapes, since the partitioning forces each row to be a single string, which obviously is not accurate here. In the example below, if this array section were strung as a 15-module string, you cannot partition it as such. I believe you used to be able to do this, did it change? Or is there a way to define this whole piece as a single string?

The Polygonal PV Plane option does not work in this case because it only creates irregularly shaped tables, not sheds. 

Please let me know if I am misunderstanding or missing something about the shade model options. In general, what is the best approach to modeling this type of system?

Thank you so much!

Rachel H. 

 

Edited April 21, 2023 by Rachel Hamilton

[Michele Oliosi]

Hi !
In fact the interpretation of partitions (or as they are called in this window "rectangle-strings" which I think we will change eventually since it is confusing) is a bit more complicated than a string.

It's worth going back to the factual definition. These partitions represent a group of PV modules (or submodules even), whose power is lost, effectively, when part of it becomes shaded.

The concept of partition mostly makes sense when the shadings are regular, i.e. they tend to cover all modules within the same group in the same way" Typically this is the case with mutual shadings, or shadings from "wide" shading objects (e.g. a row of trees, a fence, a wide parallelepiped). This is because when the shade falls on the PV tables in a regular way, then one can by simple considerations find out whether the power is lost or not.

Take for instance a string of modules in portrait: if all the bottom cells are shaded, then all submodules are limited in current because of the shaded cells. By extension, the whole string can only support as much current as the shaded cells allow. In this case part of the partition is shaded, then the whole string becomes inactive.

Now, even if you split the above string of modules in portrait into three tables (like in your example but with modules in portrait), as long as the shades that cover the tables are similar (usually because they form regular rows) the situation is the same: when all the bottom cells are shaded, then you will lose the power from the three tables.

For this reason, in the case of regular rows, no matter whether the string is split among tables, you can still safely define one partition in the length of the table, as though your strings were shorter. In the partition framework, there is usually no need to define fractions of partitions.

There can be more complications when using the partition framework to define electrical shadings. In some situations, for example for half-cut modules in portrait, or for any modules in landscape on one module-wide tables (such as your example), one should not define a single partition per string, but rather two. This is because a shadow on the bottom cells does not invalidate the power of the whole string. Due to the bypass diodes and cell layout, about half the power is retained.

TLDR: in your case, I would put two partitions in the height of the table for all of your tables. The reasons for this are:

• when the modules are positioned in rows, the shadings are usually the same for all the modules. You therefore don't need to define fraction of partitions if your strings are split across tables.
• your modules are in landscape so you can define two partitions in the height (axis Y in your screenshot) of the table. Btw this is usually beneficial to the yield.

[Michele Oliosi]

We have an article on this topic if you want to go further ! https://www.pvsyst.com/wp-content/uploads/2022/11/Article-PVSEC-2021.pdf