Interdependency of mechanical failure rate of encapsulated solar cells and module design parameters

Abstract

In recent studies the mechanical reliability of encapsulated solar cells was numerically investigated. A finite element model of a solar module with all essential components, such as cells, polymer layers and frame was created. The principle stress field in each solar cell was calculated by exposing the module to distributed pressure loads on the glass surface. By means of a probabilistic approach based on the Weibull distribution function and the size effect the stress field was evaluated and the probability of failure of each solar cell was calculated. This approach is new in the reliability evaluation of encapsulated solar cells and can enhance the module design process. Two fundamental studies were carried out varying the mounting and frame as well as the encapsulant and its thickness. The results show that there is an interdependency between the stiffness of the frame section and the type of mounting. Furthermore the recommendation for an appropriate frame and mounting selection can change if the magnitude of the load changes. It was found that there is a correlation between the stiffness of the encapsulant and the fundamental mechanical behavior of the module laminate. For high stiffness values a sandwich behavior is dominant whereas for small stiffness values a laminate behavior with shear deformation is dominant. This results in contrary thickness recommendations for different encapsulants as well as temperatures. For high stiffness values respectively low temperatures a thin encapsulant is advantageous whereas for low stiffness values at high temperatures a thick encapsulant would be better.