Daniel Montiel-Chicharro

Influence of Viscoelastic Properties of Encapsulation Materials on the Thermomechanical Behavior of Photovoltaic Modules

In this work, the mechanical properties of encapsulation materials for photovoltaic modules have been studied. A finite element model has been developed to simulate the degradation of solder bonds within modules subjected to different environmental conditions. Various polymeric encapsulants are characterized using constitutive techniques and included in the model. It is shown that the degradation rates of the solder bonds are dependent on the behavior of the encapsulant and that some encapsulants may cause higher or lower degradation than others depending on the use-environment.

Correlation of Degree of EVA Crosslinking with Formation and Discharge of Acetic Acid in PV Modules

Ethylene vinyl-acetate (EVA) encapsulated crystalline silicon PV modules see encapsulant related degradation such as the hydrolysis of EVA which leads to generation of acetic acid that corrodes cells and cell metallisation. The formation and discharge of acetic acid in PV modules during an extended damp-heat test are studied in this work in dependence of the EVA crosslinking degree. To achieve different degrees of EVA encapsulation, mini-modules were laminated under different curing temperatures. The thermogravimetric analysis (TGA) is used to estimate the vinyl acetate (VA) content of the EVA before and after damp-heat ageing, from which the formation of acetic acid is evaluated. The net accumulation of acetic acid within modules is evaluated by corrosion induced power losses. Results show mini-modules with highly cross-linked EVA form less acetic acid under damp-heat stresses, however, accumulated the highest amount of acetic acid leading to the most severe corrosion. Therefore, highly cross-linked EVA is not favoured in terms of long-term degradation due to DH stresses as it may trap the generated acetic acid within module

Adhesion requirements for photovoltaic modules of polymeric encapsulation

Adhesion requirements for PV are often discussed but a detailed quantification based on scientific principles is outstanding. A test for the realistic assessment of requirements is presented. The difference between this test and the conventional peel test is that the test is conducted in-situ during ageing experiments in the climatic cabinet at realistic operating temperatures. Weights are attached to the backsheet of tested PV mini-modules to test stability of adhesion as devices being aged. This test is designed to identify the weakest interface of the multilayer encapsulation system and investigate the difference between field tests and failures (not) observed in certification testing. A series of samples was prepared under a wide range of lamination conditions. Different failure modes and ageing characteristics were observed. Some samples suffered quick failure of the adhesive bonds in the encapsulation system while others withstood forces of 20g/cm for 1000 hours. The test allows a clear discrimination between different samples and links closely to operational requirements.

Development of Adhesive and Cohesive Failures in EVA-Backsheet Structures in Environmental Testing

The development of adhesive and cohesive failures at the EVA-backsheet interface under different damp-heat (DH) testing condition is investigated in this paper. The adhesive and cohesive failures are classified by the surface roughness of the peeled off backsheet strips. Different DH testing condition leads to different dominating failure modes. The adhesive failure is the main failure mode at lower testing temperature, which has been masked by the mixed failure mode at the higher testing temperatures due to the different temperature acceleration factor of the two processes. Development of accelerated environmental testing protocol requires the failure mode analysis to ensure the target failure mode or degradation mechanism is accelerated and not masked by any other processes.