Thermal test:-
1) Bypass diode:-
This test is a critical component determining the thermal
behavior of the module under hot- spot conditions and therefore also directly
affecting reliability in the field. The test method requires attaching a
thermocouple to the diode (s) body, heating the module up to 75°C ± 5 °C and
applying a current equal to the short circuit current Isc measured at STC for
1h.
Failures of bypass diode test still occur either by
overrating of the diode manufacturer, or incorrect electrical configuration
with respect to the module’s Isc by the module manufacturer.
2) Hot spot endurance:-
(This part was covered in diagnostic tests)
Irradiance check:-
1) Outdoor exposure:-
The purpose is a preliminary assessment of the module’s
ability to withstand exposure to outdoor conditions. However, it only involves
exposure for a total of 60 kWh/m2, which is a rather short period of time to
make any judgments about module’s lifetime. IEC 61215 requires degradation of
maximum power Pmax not to exceed 5% of the initial value. While for IEC 61646
Pmax not to be lower than the marked “Pmax – t%“.
2) UV preconditioning:-
This test is carried out to identify materials that are
susceptible to ultra- violet (UV) degradation before the thermal cycle and
humidity freeze tests are performed. IEC 61215 requires to subject the module
to a total UV irradiation of 15 kWh/m2 in the (UVA UVB) regions (280 nm – 400
nm), with at least 5 kWh /m2.
But in the laboratory test condition very low UV irradiation
is apply to the module than real exposures during the life time of the module.
Environmental test:-
1) Thermal cycling TC200:-
IEC 61215 requires the injection of a current within ±2% of
the current measured at peak power (Imp) when the module temperature is above
25°C.this test is carried out to simulate thermal stresses on materials as a
result of changes of extreme temperatures. The module is subjected to the
cycling temperature limits of –40°C ± 2°C and 85°C ± 2°C with the below
profile.
Failure rates for T C200 can be as high as 30- 40%. It is
lower for thin-film.
2) Humidity freeze:-
In this test module is subjected to 10 complete cycles
as per harmonized profile below (IEC 61646) to determine the module’s ability
to withstand the effects of high temperatures combined with humidity, followed
by extremely low temperatures. Failure rates of this test remain in the range
10- 20%.
3) Damp heat DH1000:-
This test is carried out to determine the ability of the
module to withstand long-term exposure to penetration of humidity by applying
85°C ± 2°C with a relative humidity of 85% ± 5% for 1000 hours. This test is
known for highest failure rate test which is 40-50% for both technologies.
Mechanical test:-
1) Robustness of terminations:-
This test is carried out to determine the robustness of the
module’s terminations, which can be wires, flying leads, screws, or as for the
majority of the cases: PV connectors. The terminations undergo a stress test
that simulates normal assembly and handling through various cycles and levels
of tensile strength, bending and torque tests as referenced in another
standard, IEC 60068-2-21.
2) Mechanical load test:-
This test comes after Damp Heat and therefore done on a
sample that has undergone a severe environmental stress. This test is carried
out to investigate the ability of the module to withstand wind, snow, static or
ice loads. If the module is to be qualified to withstand heavy accumulations of
snow and ice, the load applied to the front of the module during the last cycle
of this test is increased from 2400 Pa to 5400 Pa.
An issue remains with this test is that if module failed
then it may due to structural problems, or because of an inappropriate mounting
technique.
If the module is to be qualified to withstand heavy
accumulations of snow and ice, the load applied to the front of the module
during the last cycle of this test is increased from 2400 Pa to 5400 Pa.
Successful completions of IEC61215/61646 tests means
- The product has met a specific set of requirements
- Those modules that have passed the qualification test are much more likely to survive in the field and not have design flaws that lead to infant mortality.
- They suffer almost no degradation in power output from the test sequence.
Limitations of IEC61215/61646
- It does not identify and quantify wear-out mechanisms.
- It doesn’t differentiate between products that may have long and short lifetimes
- Not to address all failure mechanisms in all module designs
- Not to address failure mechanisms for all climates and system configuration
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