Solar-Cell Interconnect Design for Terrestrial Photovoltaic Modules

Abstract

An investigation of interconnect fatigue in photovoltaic systems has led to the development of useful reliability-design and life-prediction algorithms presented here. Experimental data gathered in this study indicate that the classical strain-cycle (fatigue) curve for the interconnect material fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming, a functional form is fitted to experimental cumulative interconnect failure-rate data to yield statistical fatigue curves (with failure probability as a parameter) that enable (a) the prediction of cumulative interconnect failures during the design life of an array field, and (b) the unambiguous—i.e., quantitative—interpretation of data from field-service qualification (accelerated thermal-cycling) tests. Optimal interconnect cost-reliability design algorithms are derived, intended to minimize the cost of energy over the design life of the array field. This procedure yields not only the minimum break-even cost of delivered energy, but also the required degree of interconnect redundancy and an estimate of array power degradation during the design life of the array field. The usefulness of the design algorithms is demonstrated with realistic examples of design optimization, prediction, and service qualification testing.