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GENERAL DESCRIPTION OF PV / SOLAR SYSTEM
Bypass Diodes
As mentioned, PV / Solar cells are wired in series and in parallel to form a PV / Solar
Panel (Module). The number of series cells indicates the voltage of the Panel (Module),
whereas the number of parallel cells indicates the current. If many cells are connected
in series, shading of individual cells can lead to the destruction of the shaded cell or
of the lamination material, so the Panel (Module) may blister and burst. To avoid such
an operational condition, Bypass Diodes are connected anti-parallel to the solar cells
as in Fig. 2.7. As a consequence, larger voltage differences cannot arise in the reverse-
current direction of the solar cells. In practice, it is sufficient to connect one bypass
diode for every 15-20 cells. Bypass diodes also allow current to flow through the PV
module when it is partially shaded, even if at a reduced voltage and power. Bypass
diodes do not cause any losses, because under normal operation, current does not
flow through them.
-
+
A
K
bypass diodes
load
Figure 2.7. Parallel PV cell with bypass diodes
Current (I), Voltage (V) and Power (P) Curves of a PV / Solar Panel
(Module) and how the PV / Solar Panel (Module) is rated -
V
, Vmp , I
Imp , Pmax
oc
sc ,
Fig. 2.8. Current (I), Voltage (V) and Power (P) Curves
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