## 3 Present PV Technologies
### PV Module Service Life  
PV modules are designed for outdoor use and are therefore subject to weather, climate, and many other factors. Damage to modules in operation is frequent and can affect different parts of the modules. UV exposure alters the polymers used to encapsulate the photovoltaic cells and modifies the mechanical and optical characteristics of these polymers. Moisture can penetrate the module and degrade welds, cables, and connections. Freezing can cause mechanical stress, while in the desert, sand can erode materials, etc. Stressors (sunlight, humidity, wind, snow, rain, hail, high/low temperatures, temperature changes, salt, sand, dust, etc.) interact with several factors, such as module materials, cell technology, encapsulation materials, etc.) All stress factors are singular stress parameters, but often they are present and active in different combinations. These combinations have a higher damage potential than the sum of the individual parameters [47]. Module durability is  
Figure 13: Bifacial cell structure. affected by the design, the module production process, the quality control procedures, the DC voltage between the module frame and the cells, the module assembly system, and, finally, the operational maintenance [48]. Of the components of PV modules, the encapsulants are the most susceptible to aging; therefore, most prominent PV module failure mechanisms are linked to the used polymeric encapsulation materials [49; 50]. In addition, interactions with other module components, such as ribbons or cell metallization, can result in unexpected degradation mechanisms or failure modes [51]. Detailed understanding of the degradation processes of photovoltaic modules and materials is a prerequisite for the successful development of new components and constructions, and for the fabrication of photovoltaic modules. As indicated in Section 2.3, the module service life is one of important drivers of PV technology, as prolongation of the PV module service life has a similar effect as that of increasing the module's efficiency. The present service life of c-Si modules is usually declared to be 25 years (or more). For example, bifacial modules with double-sided glass, with polyolefin (POE) encapsulation, have a service life of well over 30 years. One of the problems is that the present modules use materials and technologies that did not exist 25 years ago, and the reliability of new PV module designs cannot be proven with field data. Therefore, the data of new module types are obtained using accelerated testing, usually utilizing some international standards, which changed significantly after the solar boom in 2008. These standards gradually consider the phenomena that appear during  
Figure 14: The development of the average efficiency of the produced modules. Figure 15: Maximum module power development. real operation, to avoid their negative impact on future modules and to give the operator a guarantee of quality. For example, the potential induced degradation effect, which was unknown in 2008, was described and implemented in special international standard IEC TS 62804-1:2015 and, since February 2021, it has been implemented in the basic PV standard IEC 61215-2:2021 (the original standard is still valid, but it can be predicted that it will be withdrawn soon). Due to changes in PV module structure (different encapsulation materials, lower thickness of glass, etc. ), cycling (dynamic) mechanical load testing, bifacial modules testing, and special procedures for flexible modules were implemented. The same situation applies to the other effects and technologies. Because the development of new PV technologies is unpredictable, the previously used two standards (IEC 61215 for crystalline and IEC 61646 for thin film modules) were joined into one standard IEC 61215-1-X, whose structure allows new technologies to be added quickly. The standard procedures for testing are the same and only deviations relevant for concrete technologies apply. The \"X\" in these standards designates concrete technology.