Measurement techniques and instruments suitable for life-prediction testing of photovoltaic arrays. Interim report

To aid in meeting the need for establishing reliable tests for characterizing the response with time of present and future encapsulated photovoltaic modules, a two-phase study was conducted to identify specific measurement requirements as well as applicable or potentially applicable measurement techniques for satisfying those requirements. Phase I of the study reviewed relevant degradation modes and mechanisms, including contributing environmental stresses, and identified and recommended all techniques and instruments judged suitable for characterizing specific types and classes of degradation modes. One category of techniques identified and recommended included techniques which required some further experimental evaluation and/or developmental work in order to establish their applicability and sensitivity precision. This category of recommendations formed the basis for the Phase II evaluations. In Phase II, three techniques requiring such experimental evaluation were selected from those recommended in the Phase I study for a preliminary experimental evaluation. The techniques were selected on the basis of their potential advantage in sensitivity or in on-site applicability. Specular and nonspecular optical reflectance measurements were chosen because of their potential for on-site use in studying delamination, and other interface flaws and degradation modes. Chemiluminescence measurements were chosen for evaluating UV-radiation-induced degradative changes in polymers because they offer amore » high degree of sensitivity and precision in characterizing such changes. Electrical noise measurements were chosen for evaluating cell series-resistance changes associated with contact corrosion and/or debonding because of the inadequacy of conventional techniques and their potential adaptability to on-site use.« less