Photovoltaic Module Reliability

9Predicting PV Module Service Life

What the PV industry would like is one set of accelerated stress tests that when successfully passed would ensure that a particular module type could survive in the field for 25 years. Implicit in that statement is the assumption that the test sequence is reasonably short. Most people asking for such a test sequence are probably thinking in terms of a few months of testing with an answer that spans a reasonable range of years (something like 25–35 years). This is not likely to happen because not all modules are designed and made the same way, nor are they deployed in the same geographic locations, so they are likely to degrade or fail via different mechanisms at different rates. McMahon et al. [1] came to this same conclusion as early as 2000.

Take a quick review of Chapter 2 and you realize that modules can and do degrade and/or fail in many different ways. Each of these failure modes may be caused by a different set of environmental conditions. To predict the module's service life, we must predict it in relation to each and every one of the identified failure modes it is likely to experience. If we are going to use accelerated stress tests to predict service life in the field, we are going to have to understand the relationship between accelerated stresses and field exposure. Section 9.1 will address how to go about determining the acceleration factors for the different accelerated stress tests that are typically performed on PV modules. ...