# Progress in Improving Photovoltaics Longevity
## 1 Introduction
Enhancing the durability of BIPV systems helps to maintain their performance and reduces the frequency of costly replacements, thus improving the overall sustainability of these systems. In this context, understanding the parameters affecting degradation rates and PV lifetime becomes crucial as the energy transition to PV systems accelerates. The lifespan of solar modules is typically 25 to 30 years during which they experience a gradual degradation in efficiency. A frequently used definition of lifetime for modules/systems refers to a threshold (power loss beyond a defined limit) corresponding to 80% of the initial nominal power of the device. Typical median degradation rates of 0.5-0.6%/year range with the mean in the 0.8-0.9%/year range are reported for the conventional crystalline silicon (c-Si) modules [18]. The high-efficiency silicon heterojunction modules expected to enter the GW manufacturing scale show median and average performance loss rate values of 0.80%/year and 0.83%/year, respectively [19]. In order to increase lifetimes and decrease degradation rate, the reasons modules degrade and fail should be comprehensively understood, and designs and materials should be selected to minimize degradation and failures [20]. Each design choice impacts lifetime differently in different climates since degradation can vary significantly based on environmental factors such as temperature, humidity, and exposure to ultraviolet radiation. For instance, modules installed in hotter climates may experience degradation rates nearly double those found in cooler regions. By the end of their expected lifespan, solar panels may operate at approximately 80% of their original efficiency, still contributing to electricity generation but at a reduced capacity. However, the extreme weather climates the world experiences in the climate crisis affect the lifetime of PV modules [21]. Hence, it is essential to understand the degradation mechanisms and the effect of local climatic conditions on the longevity of PV technologies. In this context, manufacturers can be assisted in developing mitigation strategies and climate-proofing PV technologies for the most significant environmental stressors such as the temperature rise of the modules. Enhancing the durability of solar modules will not only maximize energy production but will also reduce waste and environmental impact associated with the disposal of aging systems. While several comprehensive studies have been published in the literature on PV degradation mechanisms, assessments on the factors affecting the longevity of photovoltaics, especially in building-integrated PV modules, are limited. In view of the above, this work aims to review and synthesize existing research on the factors influencing the longevity of PV systems. Through the analysis of the degradation mechanisms of solar modules, the paper provides a comprehensive overview of the lessons learned so far and identifies the research gaps and open questions. In addition, the innovative materials and technologies developed for enhancing the longevity of PV systems are assessed. This includes the advancement of solar cell materials and cooling methods as well as the best installation and maintenance practices with innovative PV inspection and cleaning methods. The remainder of the manuscript is organized as follows. Section 2 outlines the methodology for this work, while Section 3 is devoted to a concise overview of the theoretical framework regarding PV output dependence on intrinsic and environmental parameters. PV physical degradation rate is also discussed due to its pivotal role in improving PV longevity. The results are divided according to the specific objectives of the analysis and are presented in Section 4. In this section, a particular emphasis is put on highlighting the need for BIPV longevity improvement. Results are discussed in Section 5, and the main conclusions of this study are summarized in Section 6.