We distinguish between two fundamentally different types of shadings:

 - Far shadings are described by a horizon line. They concern shadings from objects sufficiently far as we can consider they act on the PV field in a global way: at a given instant, the sun is or is not visible on the field. Typically, the distance of these shading objects should be higher than, say, ten times the PV field size.
 - Near shadings are shadings produced by near objects, which draw visible shades on the PV field. We call Shading Factor the ratio of the shaded area, with respect to the total sensitive area of the field. The treatment of near shadings is much more complex than far shadings, it cannot be done without a detailed 3D description of the full PV system and its environment.

This is the most difficult part of the PVsyst software. For beginners, you have a tutorial that explains the main procedures with an example.

During the simulation, the shading calculations have to be computed at each hour and applied differently on the beam, diffuse and albedo components (see Shadings Calculation and Model).

## For the beam component of near shadings we have to consider 2 kinds of losses:

 - Irradiance losses, which correspond to the deficit of irradiance on the cells (formerly called "Linear shading losses"),
 - Electrical losses, resulting from the mismatch of electrical response of the modules in series and strings in parallel: for example, in a string of modules (or cells), the total current is always determined by the current in the weakest cell.

PVsyst provides 2 different ways to treat these electrical losses:

 - Shading factor "according to strings", which is a rough evaluation giving an upper limit to the shading loss (see Electrical shadings according to module strings),
 - Detailed electrical calculation according to the exact positioning of each module in the field  (see Module Layout  and Detailed electrical calculation).

Note that a model equivalent to the "according to strings" mode, to account for the electrical losses, may also be used with the "unlimited" orientations. These orientations are an alternative way to include mutual shadings in the simulation.

See  "Near shadings, main dialog" for the general procedure, and the different ways of performing shading calculations.