In solar PV system, it is important to analyze the shading caused by surrounding objects and/or vegetation. Shading on the photovoltaic system is the main hurdle for the power generation. It should be eliminated as much as possible. Right time to consider this issue is the system planning’s phase, later it is usually too late.
Shading of strings – if crystalline modules are mounted on the roof, they should be always mounted horizontally and never vertically. Reason is quite simple: each crystalline module usually includes two bypass diodes which are active if shading occurs. When modules are mounted horizontally the module still operates with some amount of power (50% or less) if the bottom row is shaded, because only one bypass diode is active. But if modules are mounted vertically and if lower row is shaded partially or completely both bypass diodes are active and amount of output power is close to zero.
Preferred orientation of modules in strings on the roof
String configuration – modules that are shaded more often than other parts of array should be connected into separate string(s) if possible. This will prevent losses of the whole system because of partial shading of only one part of array.
Inverter configuration – some inverter offer several inputs, for each string it have its own input. In case of shading of one string, other inputs will still operate in maximum power point situation.
Amorphous modules – In cases where shading cannot be avoided use of amorphous modules should be considered. Amorphous modules are far less sensitive on partial shading (in comparison with crystalline modules) so that even in case of partial shading they produce significant amount of power.
Array shape – In some cases, we can also prevent shading losses with carefully array design. In the case explained below have array in the shape of trapezoid, because of shading of church’s bell tower.