Photovoltaic Module Reliability

3Development of Accelerated Stress Tests

Chapter 2 identified the field failure modes that have been observed for PV modules. Once failures have been observed, it is up to the module manufacturer to develop improved designs, component materials and processes to manufacture the modules so that they do not suffer these failures. If, however, the only way to assess the impact of a product change is to deploy it in the field and wait to see what happens, improvements to the technology will take a long time. In order to speed up this process, we look for accelerated stress tests (ASTs) that cause the same failures to occur in the modules that have been observed in the field, but of course in much shorter times.

We need to look at each of the failure modes described in Chapter 2 and try to determine what stress or stresses occurring in terrestrial environments caused these failures. Was it?

• Operation at high temperature
• Changes in temperature
• High humidity
• Wind or snow loading
• UV exposure
• Or perhaps a combination of several or all of the above or something else.

Once the driving force for the failure mode has been identified, we can then try to accelerate that stress to cause the failure to occur in the laboratory in a much shorter time period.

In developing ASTs, we must cause degradation. The degradation occurring in the AST must be due to the same failure mechanism we saw outdoors. If not, our accelerated test is accelerating the wrong mechanism and we may learn nothing about ...