Climat tempéré | EPFL Graph Search

Une région soumise à un climat tempéré, encore appelée région tempérée ou zone tempérée, est dans le sens commun une partie de la surface terrestre où les températures ne sont pas extrêmes, c'est-à-dire ni torrides, ni glaciales, correspondant aux climats océanique, méditerranéen et subtropical humide selon la classification de Köppen. Ce terme est également employé pour désigner certaines zones dans d'autres classifications climatiques. Définition géographique Une zone tempérée, définie d'un point de vue strictement géographique, regroupe les régions situées entre les tropiques (23°) et les cercles polaires (66°) par opposition aux zones polaires (glaciales) et tropicales (torrides). Par convention, dans une acception plus étroite, les régions tempérées peuvent être cantonnées entre le et le parallèle, en faisant ainsi abstraction des zones subtropicales et subpolaires. Ces vastes territoires ont quelques particularités communes : le soleil se couche tous les jours, il

Reliability of photovoltaic modules

Eleonora Annigoni

A fundamental challenge with solar energy is improving the reliability, and increasing the lifetime, of photovoltaic modules. Typically, photovoltaic module manufacturers guarantee 80% of the nominal power of their modules for 25 years, but this type of guarantee is not based on a deep comprehension of the real degradation mechanisms of the modules. Moreover, the current challenge is to extend module lifetimes up to 30-40 years. For these reasons, accurate predictions of the lifetime of modules are needed. The primary goal of this dissertation is to develop predictive models to evaluate the lifetime of photovoltaic modules, taking into account the climates in which they operate. We consider the technology of crystalline silicon (c-Si) modules, which largely dominate the field. In Chapter 1 we identify two main degradation mechanisms, namely, potential-induced degradation (PID), and interconnection failures, that are particularly of interest as they can occur non only in harsh environments such as desert or tropical regions, but also in temperate climates. The main topic of this dissertation is the PID failure mechanism. Chapter 3 offers an introduction to the topic of PID for conventional p-type c-Si modules. In Chapter 4 we develop a lifetime model for PID. Such model is based on empirical equations obtained from accelerated tests in laboratory. In particular, we introduce a dependency on voltage that allows to perform PID prediction at string level, and analyze in detail the regeneration mechanism under irradiance. The result is a set of equations that describe the main phases of the evolution of PID as a function of the stress parameters. In Chapter 5, this model is applied to predict the evolution of PID for devices operating outdoors, considering four locations with different climates. One difficulty in applying our model to outdoor conditions arises from the fact that stress levels vary continuously according to the meteorological conditions, while our model was developed from indoor testing at constant stress conditions. We overcome this issue by using a mathematical method based on the concept of equivalent time. Moreover, suitable thresholds on the weather conditions are set to properly simulate the different phases of PID. In Chapter 6, we employ accelerated stress tests to investigate which strategies (selection of materials and/or module architectures) would allow us to manufacture PID-free modules. Chapter 7 is devoted to the second degradation mode under study in this dissertation, namely, disconnection failures. We validate experimentally a model developed in LT-SPICE that simulates the performance of a string with disconnected ribbons. In summary, this thesis proposes a combination of accelerated test sequence and simulations that allow to predict, for a given location, the effect of PID on the module power output. We are confident that this methodology could be applied in general to other degradation mechanisms, thereby allowing an improvement of the prediction of photovoltaic modules reliability in different climate conditions.

EPFL2018

Une nouvelle infrastructure publique sur les rives du Bouveret

Sophie Langel

Le site choisi est celui du village du Bouveret, situé dans la plaine du delta du Rhône chablaisien suisse. Ce lieu est caractérisé principalement par son isolement: d'une part par sa situation au sein d'un territoire lui-même isolé, le Chablais suisse, d'autre part par ses limites administratives, mais surtout par ses limites naturelles: la topographie, le lac Léman, le Rhône et la réserve des Grangettes. Cet isolement ainsi que la diversité des ressources naturelles du site participent fortement à l'identité du village et nourrissent un imaginaire lié au thème des loisirs favorable au tourisme mais aussi à l'accueil d'une nouvelle population amenée par la pression du développement de la métropole lémanique sur le Chablais. L'intention du projet est celle de reconnecter le village à ses atouts naturels que sont le lac et le Rhône, grâce au développement d'un réseau de mobilité à travers la plaine basé sur les connections existantes, et d'implémenter de nouvelles connections. A l'image d'une coulée verte, ce réseau a pour but de revaloriser une partie des espaces du domaine public par quatre types d'interventions: le développement de la mobilité douce, la requalification des parkings, la création de parcs et zones humides et la densification/sauvegarde de certaines aires. Les futurs travaux de la 3e correction du Rhône ont pour objectif de rendre au fleuve un aspect plus naturel et proche de ce qu'il était auparavant; ce projet de naturalisation de la plaine du Bouveret s'inscrit dans cette vision.

2015

The role of Encapsulants in the long-term performance of advanced Crystalline Silicon Glass-Glass PV modules

Luca Gnocchi

The adoption of crystalline silicon (c-Si) PV modules based on glass-glass (G-G) structures is gaining momentum because of the possibility to manufacture bifacial panels, collecting light from the rear side. Despite not being an optimal material, Ethylene Vinyl Acetate (EVA) has become the dominant encapsulant in the PV industry. In fact, upon exposure to UV at high temperatures in the presence of moisture, EVA generates acetic acid (HAc), leading to the corrosion of the metallic interconnects. This problematic may be even more pronounced in a non-permeable G-G structure, compared to a conventional glass-backsheet (G-BS) design, in which HAc can be partially degassed out through the breathable BS. Nevertheless, some industries would like to continue using EVA in the manufacturing of G-G modules, because of the lower cost, the much longer track record and easier processability of EVA compared to newer alternatives, such as polyolefns (POs). In this work, we try to answer the question whether it is possible to use EVA in the manufacturing of G-G modules. The experimental chapters focus primarily on study the long-term reliability, in particular:1. The sensitivity to water of different c-Si cell technologies (i.e. Aluminum Back Surface Field (Al-BSF), Passivated Emitter Rear Cell (PERC) and Silicon Heterojunction (SHJ)) exposed to damp-heat, where we highlight the good stability of the EVA, and the sensitivity to moisture of the SHJ solar cells.2. We propose a detailed microscopical model explaining the problematic of the SHJ to water. In reality, the presence of moisture (favored by the use of EVA) is only a contributing factor, as clearly indicated by the fact that the degradation in more pronounced in the presence of glass. Here we point at the role of a glass corrosion process and of NaOH in damaging the passivating properties of the cell. Either by reducing the water ingress (with an edge seal or a PO) or by replacing the glass type, the degradation phenomenon is not observed.3. The impact of EVA storage conditions on the lamination quality and ultraviolet (UV) degradation. If good polymer storage and handling practices are carefully respected, the results tend to suggest that EVA can still be a viable solution to encapsulate G-G PV modules, for deployment in geographical zones where the humidity levels are not so high during the year (i.e. temperate climates). On the contrary, if these conditions are not observed, or in the event of module operating in a hot-humid climate, we believe that this may affect the long-term performance of G-G modules encapsulated with EVA.4. An accelerated aging test for acetic acid corrosion (missing in the industry standards) is developed to probe wear-out and end-of-life behavior and facilitate screening of metallization, and interconnection technologies. Corrosion is in fact one of the main end-of-life failure modes in PV modules which use EVA. Here, SHJ cells with a low temperature silver paste-based interconnection outperformed cells with conventional solder-based interconnection (i.e. Al-BSF and PERC). The proposed corrosion test method can be optimized to match corrosion behavior observed in feld modules with shorter times than standard damp heat tests.These results give us a deeper insight on how to manufacture reliable and durable G-G modules, based on different cell technologies, and do not rule out the possibility to use EVA when targeting extended lifetimes of double glass panels.

EPFL2022