Solmetric PVA-600, Руководство пользователя

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5 Interpreting Measured I-V Curves
5-17
One or More Cells or Modules Are Completely Shaded
Shading a cell or module with very high opacity (hard shade) causes its bypass diode to
begin conducting when any current passes through it. In this case, the notch in the I-V
curve discussed in 4. The I-V Curve Has Notches or Steps occurs at zero amps. As such,
it may be difficult to differentiate the shape of this notched I-V curve from a normal
curve with a reduced Voc.
One or More Bypass Diodes Are Conducting or Shorted
Failure modes within individual PV modules may cause a bypass diode(s) to conduct
even in the absence of shade or severe module-to-module mismatch. The I-V curve shape
may look normal except that the Voc value is lower than predicted. If the reduction in
Voc is approximately equal to a multiple of the Voc of a module cell string (in 72 cell
modules, typically Voc/3) look for a module(s) with conducting or shorted bypass diodes.
Start by inspecting module front and backsides for burn marks. You can also use
selective shading to locate the module(s). When completely shaded, good modules will
drop the string's Voc value by similar amounts. In contrast, a module with conducting or
shorted bypass diodes will reduce the string Voc by a smaller amount when shaded, due
to the fact that one or more of its cell strings are not contributing voltage.