Stress analysis of encapsulated solar cells by means of superposition of thermal and mechanical stresses

Abstract

Within this contribution several 3D finite- element- models have been created in order to simulate processing of solar cells (lamination, soldering) as well as mechanical bending. The stress state for each load case was analysed with respect to magnitude and direction of principal stresses. For the process steps there are different mechanisms that induce stresses in the silicon. For soldering the mismatch in CTE is dominant. For lamination, bending around the ribbon is the dominant mechanism, which is due to the contraction of the encapsulant. Furthermore, it was found that cooling during lamination applies the highest loads into a solar cell. Mechanical bending was simulated and investigated experimentally by 4-point-bending with different load ramps. Due to strain-rate dependent properties of the encapsulant EVA there is a minor in fluence on the load deflection behaviour but a large influence on the reliability of a solar cell. By means of a parameter study the influ ence of the cell distance on mechanical reliability was investigates. It was shown that a small cell distance (here < 3mm) increases the probability of failure of the solar cell significantly

A novel test method for quantifying cracking propensity of photovoltaic backsheets after ultraviolet exposure

“…The total UV dose for a 510‐hour exposure on the NIST SPHERE is equivalent to 5 to 6 years of field exposure when a 12% albedo for the reflected light on the backside of a PV module is assumed . Finite element analysis results show that the residual thermomechanical strain in the backsheet of a typical silicon PV module to be in the order of 0.1% . In the cell‐gap region, relatively large strain that is higher than the strain in the backsheet region can be produced when temperature changes .…”

“…5,10 Finite element analysis results show that the residual thermomechanical strain in the backsheet of a typical silicon PV module to be in the order of 0.1%. 45,46 In the cell-gap region, relatively large strain that is higher than the strain in the backsheet region can be produced when temperature changes. 47 Critical surface cracking strain is measured to be 0.14% to 0.31% (c.f.…”

Degradation in photovoltaic encapsulation strength of attachment: Results of the first PVQAT TG5 artificial weathering study

“…The mechanical stress and strain in modules was examined using finite-element analysis in Refs. [38], [39], [40]. Table I summarizes key differences identified between the mechanical state invoked in the CST method and that common to PV modules.…”

“…The specimen curvature tends to be minimal for glass/encapsulant/glass CST specimens, where curvature provides relatively little influence on the test [7]. Specimen curvature instead varies with thermal misfit and residual stress in a glass/encapsulant/backsheet PV module, which are major sources of stress variation through module lifetime [40]. The dominant stress in CST is an applied shear, as dictated by the test geometry.…”

A Rational Strength Prediction Approach to the Design of Double-Glass Photovoltaic Modules

“…In a glass-backsheet structure, an encapsulant and backsheet are attached outside the glass, and they have relatively small influences on the total module strength due to the high mismatch in moduli of the materials. On the other hand, in the double-glass structure, an encapsulant located in the middle of a module plays a much more critical role in transmitting shear stress from the upper glass to the lower glass when a specific load is applied to the module [1]- [4]. Thus, the stiffness of an encapsulant plays a determining role of module stiffness and associated load resistance (strength) in the double-glass structure.…”