Z200 PV Analyzer
User Manual
R
S
<
150Ω
This estimate is generally applicable regardless of technology i.e. it applies to both crystalline
and thin film technologies. However, there is significant variation between technologies. For in-
stance, PV modules based on mc-Si cells typically has an R
S
value of half of the above estimate
or less.
Obviously, when there are many PV strings of similar construction in a test-site it is also possi-
ble to find potential outliers by comparison of measurement data. If R
S
is found to be too high,
it is an indication of a problem e.g. with shading or bad cabling/connectors. If the impedance
exceeds 10 k
Ω
at
f
= 100 Hz, there may be a disconnect in the string e.g. in the form of a bad in-
ternal junction, a broken cable or faulty connector. See info box below for tips on how to quickly
locate the fault. R
P
is the string parallel (shunting) resistance; a value that will be several k
Ω
per
PV module when the solar cells are in a healthy condition. The effect of R
P
is only seen in strings
that are partially or fully shaded or at nighttime. R
P
is estimated at low frequencies where the
effect of C
d
the diffusion capacitance is minimal.
INFORMATION.
•
If R
S
is greater than expected, there could be prob-
lems internal to one or more modules e.g. with bro-
ken bus-bars or corrosion. The operator is encour-
aged to do a quick baseline measurement in the ”By-
pass Diode test” function. If the R
S
value in this test
looks OK, then proceed with the rest of the , which
will locate all poor performing modules.
•
If R
S
remains high in the ”baseline” measurement and
is above 10 k
Ω
, then there is probably a disconnect
somewhere in the string external to the modules. In
this case, the operator is advised to run the ”Discon-
nect” application in order to position the fault.
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