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|Title: ||Thermomechanical degradation mechanisms of silicon photovoltaic modules|
|Authors: ||Owen-Bellini, Michael|
|Issue Date: ||2017|
|Publisher: ||© Michael Owen-Bellini|
|Abstract: ||The durability and lifetime of photovoltaic (PV) modules is one of the chief concerns for an industry which is rapidly approaching maturity. Guaranteeing the economic viability of potential PV installations is paramount to fostering growth of the industry. Whilst certification standards have helped to improve the reliability of modules, with a significant reduction in early failures, long-term performance degradation and overall lifetimes are yet to be addressed in a meaningful way. For this, it is necessary to quantify the effects of use-environment and module design.
Long-term degradation of the solder bonds in PV modules causes steady power loss and leads to the generation of more devastating, secondary mechanisms such as hot-spots. Whilst solder bond degradation is well-recognised and even tested for in certification protocols, the potential rate of degradation is not well understood, particularly with respect to different environmental conditions and material selection. The complex nature of a standard silicon PV module construction makes it difficult to observe the stresses experienced by the various components during normal operation. This thesis presents the development of a finite-element model which is used to observe the stresses and strains experienced by module components during normal operating conditions and quantifies the degradation of solder bonds under different environmental conditions.
First, module operating temperatures are examined across a range of climates and locations to evaluate the thermal profiles experienced by modules. Using finite-element techniques, the thermomechanical behaviour of modules is then simulated using the same thermal profiles and a quantification of solder bond degradation potential in each location is achieved. It is shown that hot climates are responsible for the highest degradation potential, but further to this, hot environments with many
clear sky days, allowing for large swings in module temperature, are significantly more damaging. A comparison is drawn between indoor accelerated stress procedures and outdoor exposure, such that an equivalence between test duration and location-dependent outdoor exposure can be determined. It is shown that for the most damaging climate studied, 86 standard thermal cycles is appropriate for one-year of outdoor exposure whereas the least damaging environment would require 11 standard thermal cycles. However, these conclusions may only be applicable to the specific module design which was modelled as the material selection and interaction within a device plays a major role in the thermomechanical behaviour and degradation potential.
In addition to a study on the influence of use-environment, a study on the influence of the encapsulating material is conducted with a particular focus on the effects of the viscoelastic properties of the materials. It is shown that the degradation of solder bonds can vary depending on the encapsulating material. Furthermore, the intended use-environment could inform the selection of the encapsulating material. The temperature-dependency of the material properties means that some materials will mitigate thermomechanical degradation mechanisms more than others under certain conditions i.e. hotter or colder climates.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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