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Bypass diodes

A bypass diode conducts current past an inactive cell in order to:
  • prevent the hot spot effect and
  • to minimise power loss if a cell becomes inactive

Figure 1: Junction box with integrated bypass diodes

Source: prevent 2009

Hot spot effect

If an inactive cell (e.g. due to shading) is fed current by the other, active cells, it converts this energy into heat. The worst case scenario is that a hot spot builds up in the inactive cell that can destroy the module. To avoid this, bypass diodes are used that duct the current past the cell string containing the inactive cell.

Minimising power loss

Without a bypass diode, a single shaded cell would reduce power production of the entire series connection to a minimum. Thanks to the bypass diode, the total power yield only decreases by the lost yield of the bypassed cell string.
Figure 2: Shading with and without bypass diode

Source: pv_verband 2009

Last page update: 25.01.2011