Electrical shadings: Module Layout

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Electrical shadings: Module Layout

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The Module Layout tool is aimed at the detailed calculation of the Electrical shadings mismatch loss.

It requires a description of the position of each PV module in the 3D scene, and the module interconnection as strings according to the inverters defined in the "System" part.

General description

The evaluation of the electrical shading loss requires the calculation of the I/V characteristics of the PV array, by the addition of the voltage (I/V curve) of each module in a string, and then the addition of the current of each string  (see XXX).

The I/V curves depends on the partial shading on each PV module. Therefore we have to know the exact geometric position of each module, and the string it belongs to.

Therefore, this definition of the "Module Layout" part is based:

-on one hand on the the shadings 3D construction for the positioning,
-on the other hand on the electrical definitions of the sub-arrays (PV modules and inverters) in the "System" option.

These parts of the project should be well defined before the elaboration of the Module Layout tool. Any posterior modifications of these parameters may have consequences on the Module Layout definitions. The Module Layout is the last step of your development for the study of a PV system.


When opening this tool, you get a 2D representation of all fields that you have defined in your 3D scene. Each 3D sub-field element (for example a shed or a tracker) is named a "Table".

If you have defined several orientations, you will have a specific representation for each orientation.

The blue panel on the top right gives you some information about the actual state, and advices for the next action to be done.

There are 2 main steps to follow:

-"Mechanical" page shows the rough tables from the 3D scene, and requires to position all modules as defined in the "System" part,  for each orientation.
-"Electrical" page is meant for the attribution of each module to a specific String  (acc. to the inverter's definitions in "System").

Moreover, there are pedagogic tools, not necessary for the preparation of the Module Layout parameters for the simulation:

-"Shadings 3D" shows the real shadings on all tables of a selected MPPT input, and the corresponding I/V curves for each shaded PV module.
-"I/V curves" shows the detailed I/V curves for this MPPT input, as addition of voltages all modules in series in each string, and addition of currents for each string in the MPPT array.  

The electrical calculations are done taking the beam and diffuse components into account. Even when a sub-module is completely shaded (regarding the beam component), there is a remaining diffuse irradiance which ensures a minimum current in this string. The diffuse incident irradiance is coming from all directions, it is supposed homogeneous and to be affected by a constant shading factor, calculated once only for the whole year. Eventual albedo is also evaluated using a constant shading factor.

These Module Layout definitions are mainly used within the simulation, for the detailed calculation of the mismatch electrical shading losses.

Module Layout definitions output

Incidentally, this tool may be also useful for an easy design of the module's wiring organization within your real PV system.

The ModuleLayout definitions may be printed independently, or may be shown in the final simulation report if desired, in different pre-defined ways.


Thin film modules

This tool is suited for crystalline modules only, with usual rectangular cells.

It is not applicable to thin film modules, where each cell is a strip of typically 10 mm width, along the length of the module. In this case the electrical mismatch loss is null if the shades are perpendicular to the cells, i.e. if all cells are identically illuminated (Cells  in portrait in a row arrangement). However the shading loss will be maximal if the shade is parallel to the cell, as one only cell in series may be shaded and block the current for the whole module.

Thin shadows

Due to the way shaded sub-modules are recognized, the module layout will underestimate the impact of long and thin shadings (e.g. poles).

Very large systems

The Module Layout is only useable with systems of the order of few MWp at most. Either because of the complexity of defining all the PV modules location definition if these are not regularly interconnected, or due to the computing time during the simulation. PVsyst fixes a "reasonable" limit of around 1 MWp, and an upper limit  (that you can modify in the advanced parameters) of 5 MWp. The limits can be modified via the advanced parameters "Power limit for Module Layout warning" and "Power limit for Module Layout error".

For very large systems, we advise to define a representative sub-system (for example corresponding to a single central inverter), execute the simulation and evaluate the Electrical shading loss with both tools: Module Layout and partitions. This will allow to evaluate the "Fraction for electrical effect" representative of your system (usually close to 100% for regular systems).  

Then you can simulate your full system using the option "According to module-strings", i.e. the partition model, applying this pre-evaluated factor. This latter calculation requires about the same computing time as the linear shadings option.