Diagnostic tests:-
1) Visual inspection:-
The purpose is to detect any of the “major visual defects”
defined above by checking the module in a well illuminated area (1000 lux).
It is frequently occur throughout the procedure.
2) Hot spot endurance:-
Technically hot spot occur due to the operating current of
the module exceeds the reduced short –circuit current of a faulty cells. This
will force the cell(s) into a reverse bias condition when it becomes a load
dissipating heat. Serious hot spot phenomena can be as dramatic as outright
burns of all the layers, cracking, or even breakage of the glass. This test is
carried out to determine the module’s ability to withstand localized heating
caused by cracked, mismatched cells, interconnection failures, partial
shadowing or soiling.
Electrical test:-
1) Insulation resistance:-
This test is carried out to determine whether a module has a
sufficient electrical insulation between its current-carrying parts and the
frame. A dielectric strength tester is used to apply a DC Voltage source of up
to 1000 V plus twice the maxim um system voltage. After the test, there shall
be no breakdown, nor any surface tracking. F or modules with an area larger
than 0.1 m2, the resistance shall not be less than 40 MΩ for every square meter.
2) Wet leakage current test:-
In this test the module is submersed in a shallow tank to a
depth covering all surfaces except cable entries of junction boxes not designed
for immersion. A test voltage is applied between the shorted output connectors
and the water bath solution up to the maximum system voltage of the module for
2 minutes.
To pass this test the insulation resistance shall be not
less than 40 MΩ for every square meter
for modules with an area larger than 0.1 m2. There is not any IEC standard for
PV connectors, but there is a harmonized European standard (EN 50521) for it.
The wet leakage current test is ranked as one of the most
reoccurring failures during PV qualification at the testing laboratories
Performance
parameters tests:
1) Maximum power Pmax:-
It is common practice among PV laboratories to perform it at
1000W/m2, 25°C cell temperature, with a reference solar spectral irradiance
called Air Mass 1.5 (AM1.5), as defined in IEC 60904-3. A correct and traceable
Pmax measurement to the World PV Scale is of critical importance. Not only is
it one of the pass/fail criteria, but the measured values can also be used by
the end users as a performance indicator for power yield evaluations.
Due to its importance it is perform frequently in the
process.
2) Temperature coefficients:-
This test is carried out to determine the temperature
coefficients of short- circuit current Isc (α), open-circuit voltage Voc (β)
and maximum power Pmax (δ) from module measurements. over an interval of 30°C
(for instance, 25°C-55°C), and at every 5°C intervals, the sun simulator takes
an I - V measurement (Isc, Voc, Pmax are not reflected, but measured during the
I-V sweep) including Isc, Voc and Pmax. The values of Isc, Voc and Pmax are
plotted as functions of temperature for each set of data. The coefficients α, β
and δ are calculated from the slopes of the least squares fit straight lines
for the three plotted function.
3) Nominal Operating Cell Temperature (NOCT):-
NOCT can be used by the system designer as a guide to the
temperature at which a module will operate in the field and it is therefore a
useful parameter when comparing the performance of different module designs.
The test setup requires data logging and selection for irradiance
(pyronameter), ambient temperature (temperature sensors), cell temperature
(thermocouples attached on the back side of the module corresponding to the two
central cells), wind speed (speed sensor) and wind direction (direction
sensor).All these quantities shall be within certain intervals in order to be
acceptable for the calculation of NOCT.
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