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Shading

The PV system should be planned so that it remains free of shadows throughout the day. Simulation programs provide detailed figures. As a general rule, special attention should be given to the surrounding buildings and vegetation. Often, vegetation causes shadows only after some time. Shadows that may be caused by the building itself should also be examined. Reasons for such shading can be the geometry of the building and structural details (e.g. suspended elements) (source: WM Baden-Württemberg).
Figure 1: Shading due to poor planning

Source: IEA, PVPS

Crystalline modules

The weakest cell in the string of solar cells determines the total electricity in the module. The cell can be weakened by (partial) shading, for example. In this case, the decrease in electricity is not linear, but disproportionate to the shaded module area.
Figure 2: Influence of partial shading on crystalline module output

Source: WM Baden Württemberg

Thin-film modules

Partial shading causes a comparably smaller decrease in output in thin-film modules. Due to the strip-like cell layout in thin-film modules, it is less likely for a whole cell to be completely shaded. The decrease in output is therefore usually only proportionate to the shaded area.

Connection

If partial shading in unavoidable, the PV modules and PV generators must be connected so as to allow for this shading.
Figure 3: Connection of PV generators in shaded situation

Source: arsenal research

Last page update: 08.02.2011