While the rapid test largely reveals the weaknesses of a specific module type in regard to production errors, the endurance test allows an even better estimate of the expected service life to be obtained.
Today, module manufacturers grant performance guarantees for 20, 25 and even 30 years. Some even promise an operating life of 40 to 50 years. For the calculation of electricity generation costs, it makes an enormous difference how realistic such statements are.
A test sequence that allows conclusions to be drawn about the service life was developed within the “PV Reliability” research project, which provides the basis for the PHOTON service life test. The basic principle is that all loads occurring under practical conditions are applied to the same sample over and over again – until a decrease in performance becomes apparent. The later a module buckles, the longer it will last in real-life operation.
The test uses two specimens from the rapid test, the first and second test string. The test is therefore only performed on modules that have survived the mechanical stress of the vibration test and junction box test.
Procedure of the PHOTON endurance test (silver standard)
The modules undergo the following test cycle:
Cycle 1:
- Damp heat: 1,000 hours
- Hail test
- UV: 15 kWh/m2
- Temperature cycles: 100
- Mechanical load: 5,400 Pa (simulation for heavy snow load)
- Characterization: I-V curve / electroluminescence / wet leakage
Cycle 2 to 4:
- Damp heat: 500 hours
- UV: 15 kWh/m2
- Temperature cycles: 100
- Mechanical load: 5,400 Pa
- Characterization: I-V curve / electroluminescence / wet leakage
After the fourth cycle, a hot-spot test is also performed.
Studies made during the PV reliability project have shown that after 20 years, a module reaches a humidity level of between 35 and 55 percent. The first cycle therefore ensures a corresponding humidity level in the module through 1,000 hours of damp heat. Water is an important component in the chemical reaction, which leads to signs of aging. The module is therefore subject to a further 500 hours of damp heat in three further cycles. By way of comparison, IEC 61215 only specifies a total of 1,000 hours of damp heat.
The test specimens are also exposed to UV radiation. UV-absorbent additives are one of the most expensive components of EVA encapsulation material and their use is therefore often kept to a minimum by module manufacturers for cost reasons. However, the additives lose effectiveness over time due to UV exposure and will, at some point, stopped working. The more UV absorbers the encapsulation material contains, the longer the module lasts.
Finally, the temperature cycles ensure that the material is subjected to thermo-mechanical stress. Each solar module is composed of several layers such as backsheet or rear glass, embedding material, cells and front glass, each with different thermal coefficients of expansion. If, for example, if there is insufficient embedding material, the cells are subjected to increased stress and can crack.
The test, which is also carried out with a mechanical load of 5,400 Pascal – equivalent to a pressure of around 540 kilograms per square meter – simulates high snow loads such as those occurring in alpine regions.
After each cycle, the I-V curve is recorded and an electroluminescence image is produced.
➡ Overview of PHOTON module tests
Contact us
We will be happy to answer any questions you may have regarding PHOTON module tests.
Julio Magdalena de la Fuente
phone +49-241-4003-401
julio.magdalena@photon.info