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 which explains the main procedures on 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: 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 for treating these electrical
losses:
| - |
Shading factor "according to strings", which is a rough
evaluation giving an upper limit to the shading loss, |
See "Near
shadings, main dialog" for the general procedure, and
the different ways of performing shading calculations.
