Solmetric PVA-1000S, Руководство пользователя

Страница: 142 / 152

7 Interpreting Measured I-V Curves
7-14
PV Cell Temperature Is Hotter than the Measured Temperature
The module V
oc
is dependent on the temperature of the solar cells, with higher
temperatures resulting in a lower V
oc
. It is possible that a poor thermal connection exists
between the temperature measurement device and the back of the module. Also, if the
temperature measurement is taken on the front side of the module, direct sunlight on the
temperature sensor could result in erroneous temperature readings. It is also possible that
the PV module under test has a poor thermal connection between the back of the module
and the actual PV junction.
One or More Cells or Modules Are Completely Shaded
Hard shade on an entire cell causes its associated bypass diode to begin conducting a very
low current, making it look like V
oc
has shifted downward. If you are uncertain, check the
value of V
oc
that the PVA software lists in the Table tab. This value is measured under
open circuit conditions, just a moment before the I-V measurement actually begins.
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 V
oc
value is lower than predicted. You can use selective
shading to locate the module(s). This troubleshooting method involves taking I-V
measurements of the string, shading a different module each time. The I-V curves taken
with the normal modules shaded will all look alike.