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A better understanding of moisture ingress in photovoltaic modules is crucial for better predictions of their long-term behavior in the field. Current calculations and simulations of moisture uptake in photovoltaic modules are based on the Fickian diffusion model in a homogeneous material. In this article, in situ humidity measurements in four diff...
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... is extracted from the previously obtained curves during the parameter analysis at first. Then, the trends of parameter variations and interaction between the parameters is analyzed in more depth close to this point. These trends are used to find a good fit between measurement and simulation, visually and with a minimized root-mean-squared error. Fig. 6 shows a flowchart of the optimization ...
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... It can ingress through the polymeric backsheets or edge seals and diffuse further through the encapsulants. This process can take several years before reaching equilibrium, depending on the materials and the module temperature (T), causing a possible discrepancy between the RH in the surrounding air and the corresponding moisture content at various locations inside the module [15], [16], [17]. ...
... One minimodule is protected by a white PPE (PET-PET-EVA) with a 290 ± 10 μm thickness and the other with black TPT (Tedlar-PET-Tedlar) backsheet with a 300 ± 10 μm thickness. The third minimodule contains a thermoplastic olefin (TPO) encapsulant (450 μm sheet thickness) instead of EVA to evaluate a material, which has shown non-Fickian water diffusion behavior in a laboratory setting [17]. ...
... The results showcase the high accuracy of the Fickian diffusion model in the field in the materials used, i.e., PET based backsheets and EVA. Some minor differences stemming from the model are expected, as they have been emphasized when evaluating it in large step increases between two different values of the RH [17]. Such large step changes between two stable values at constant T are usually not seen in the field. ...
Moisture plays a critical role in the degradation process of photovoltaic (PV) modules in field conditions. A commonly used approach is to evaluate the properties of PV materials by conducting tests in climatic chambers, and then apply the Fickian diffusion model in simulations to replicate field conditions, however, without experimental verification. This study describes an experimental setup for in situ measurement of moisture in fielded minimodules, using miniature temperature and humidity sensors encapsulated within the modules. Five identical setups are deployed in different climatic regions around the world, enabling a quantitative evaluation of moisture diffusion in the field and a comparison of different climates. The relative humidity measured beside the cell follow weekly weather trends due to breathable backsheet, whereas the sensors in front of the cell react much slower to outside changes and follow seasonal trends. We show that a single 2-D simulation, which is a standard practice in published studies, is insufficient to accurately depict moisture diffusion in front of the cell. Therefore, a two-stage 2-D simulation model, combining Fickian diffusion in vertical and horizontal cross section with carefully set boundary conditions, was introduced. A comparison with measurement results showed the simulation approach to be a good compromise between the simulation accuracy and speed. Finally, the results underscore the significance of understanding the local microclimate surrounding the modules, including the interface between air and backsheet, which is necessary for precise moisture diffusion simulations.
... Many activities have been reported on theoretical moisture ingress into the polymeric components [22] and the influence of the ingress mainly as material defect-based research [23]. However, the interlink and proof of actual water concentration in the fielded modules and reliable measurements methods are still under investigation [24]. Further, only few papers can be found which analyze the influence of the sole humidity conditions and their effects on degradation/performance of modules in the field in a detailed way. ...
... For PV modules, the microclimatic load is not identical with the ambient humidity conditions hence calculations using irradiation and temperature data are necessary to estimate microclimatic humidity loads. Such calculations are partly used to create degradation risk data sets and maps [4,24] and supported by measurement technologies [27]. ...
The market for Photovoltaic systems has experienced an enormous growth worldwide and will further grow over the coming decades. Investments in Photovoltaics became an important financial product with the special feature of very long contract durations. Typically operation of over 20 years is expected, during which generation of electricity and revenues are expected. Due to these long operational times, quality, durability, reliability, and degradation rates become crucial for the investment. PV modules are the dominating components in this regard since they prevail the investment. Accelerated ageing tests are in general used to ensure the quality of photovoltaic components. These tests are partly standardized, for PV mainly by IEC and are used for type approval or safety testing. Accelerated ageing tests are also adapted to specific needs and e g used for Quality Assurance (QA) of manufacturers or Service Life Prediction (SLP) by manufacturers or research institutes. All the efforts are taken to gain knowledge about the behaviour of PV modules in operation and thus the accelerated tests have to be related to normal operation. Since PV is used around the globe, the conditions vary significantly depending on the location of installation. In addition, the installation has severe influence on the operational conditions of PV modules. The papers attempt is to give an overview on the state of the art of accelerated testing and field performance analysis of PV modules with focus on developments over the last five to ten years. Developments are described and the status is analysed regarding the significance of tests including the latest developments and open scientific gaps related to the envisaged correlation of accelerated tests with field performance. The reader is enabled to differenciate between reliability testing and service life prediction. The understanding for a comprehensive approach of reliability testing including field evaluation data is develope
... Earlier works on modeling the moisture ingression in silicon photovoltaic module has predominantly being performed through finite element method (FEM) simulation [9][10][11]. Extensive research with FEM simulation has been reported with a focus on analyzing the amount of moisture that ingress into the photovoltaic module with varying diffusivity of the polymeric materials and climatic conditions [12][13][14]. FEM simulations are time consuming and resource intensive while analytical solutions provide a fast and easy alternative to FEM based modeling [1,2]. ...
The moisture ingression into photovoltaic module has significant impact on the reliability as it participates in multiple degradation pathways. Damp heat test is performed at a temperature 85°C and relative humidity of 85% for 1000 h to assess the ability of a photovoltaic module under humid conditions. In this paper, we have developed an analytical model to quantify the amount of moisture ingressing into a photovoltaic module with a breathable backsheet under damp heat testing condition. The analytical model is developed with the consideration that the vertical moisture diffusion in the ethylene vinyl acetate (EVA) layer is instantaneous. The comparison with numerical model validated the assumption. The analysis of the simulated profile with the developed analytical model showed that at 85°C, the moisture profile within the rear EVA and backsheet reaches a steady state value within 10 h. Considering that the damp heat test is performed for a span of 1000 h, to simplify we can consider that the moisture profile is temporally and spatially constant in the backsheet and rear EVA, with the moisture concentration being given by the product of moisture solubility (S) and permeability (P) for that particular material at 85°C. However, the moisture profile for top EVA in regions above the solar cell does not reach a steady state value even within a span of 1000 h. The non-uniformity of the moisture profile needs consideration for quantifying the degradation in the regions of top EVA that is directly above the solar cell.
... Most of these investigations are focused on the performance monitoring, operation, and maintenance of PV plants (Annigoni et al., 2015;Eder et al., 2019). Even though there is yet to be any formal working documents on moisture ingress reliability of PV modules (Lyu et al., 2020), there have been a lot of work that have been done in this respect over the past decades (Dadaniya and Datla, 2019;KEMPE, 2006;Kumar et al., 2019;Mitterhofer et al., 2020;Annigoni et al., 2015;Jankovec et al., 2018). A collection of these works is represented in Fig. 3. ...
... However, these polymeric components (as shown in Fig. 1) are not perfectly air-/water-tight, and are prone to permeation of gases, including moisture, oxygen, and other gaseous species from the ambient surrounding (KEMPE, 2006;Yang et al., 2020). Some of the predisposing factors are the climatic conditions, the age of the modules, the materials used for the PV module (especially the polymeric materials), and the solar cell and module technology (Mitterhofer et al., 2020;Peike et al., 2013b;Tracy et al., 2018). ...
... Fickian diffusion models are those that obey the Fick's laws: Eqs. (1)-(3), otherwise, they are known as non-Fickian diffusion models (Kempe et al., 2018;Mitterhofer et al., 2020;Slapsak et al., 2019;Jankovec et al., 2018). According to Mitterhofer et al. (2020), the Fickian diffusion models can accurately model the behaviour of moisture or gaseous species across the interface, in channels and bulk of the polymeric material. ...
Moisture ingress in photovoltaic (PV) modules is the core of most degradation mechanisms that lead to PV module power degradation. Moisture in EVA encapsulant can lead to metal grids corrosion, delamination and discolouration of encapsulants, potential induced degradation, optical and adhesion losses. The present work is a review of literature on the causes, effects, detection, and mitigation techniques of moisture ingress in PV modules. Literature highlights on determining the diffusivity, solubility, and permeability of polymeric components of PV modules via water vapour transmission rate tests, gravimetric, and immersion methods, have been presented. Electroluminescence, photoluminescence, and ultraviolet fluorescence spectroscopy, as well as dark lock-in thermography are some techniques used to detect moisture ingress in modules. Encapsulants with excellent moisture barrier and adhesion characteristics, desiccant-stacked polyisobutylene sealants, imbedded moisture sensors, and PV designs with/without breathable backsheets are ways of preventing/detecting moisture ingression in PV modules. Areas of focus for future research activities have also been discussed.
... considering a constant diffusion coefficient, has been developed previously and is widely used for estimation of moisture concentration within a PV module. The specific model seems to describe adequately the moisture ingress within a PV module, in comparison to moisture sorption measurements, although a slight overestimation or underestimation is observed for different types of polymers [91], [92]. To correct this problem, Mitterhofer et al. [92] have presented an alternate model which models transport with two different diffusion coefficients, one within the bulk material and one within channels which represent porous voids that hypothetically exist in the polymer. ...
... The specific model seems to describe adequately the moisture ingress within a PV module, in comparison to moisture sorption measurements, although a slight overestimation or underestimation is observed for different types of polymers [91], [92]. To correct this problem, Mitterhofer et al. [92] have presented an alternate model which models transport with two different diffusion coefficients, one within the bulk material and one within channels which represent porous voids that hypothetically exist in the polymer. The simulations show good agreement with the moisture sorption measurements, for different polymers. ...
... Moreover, the nature of the physics that the diffusion follows is under question, as there are a number of publications that suggest that diffusion coefficients of the polymers may vary with the moisture content [105], [90], [106], or that the moisture ingress follows a dual sorption process [92]. However, more detailed material analysis on the polymers is demanded, to investigate their behaviour and suggest the most appropriate model. ...
The work presented in this thesis comprises research into degradation paths that cause corrosion of different components of solar photovoltaic (PV) cells and quantifies the impact of corrosion on the energy yield of PV modules.
PV modules are exposed to different climatic conditions when they are installed in the field. This exposure causes various degradation modes which affect their reliability to produce electricity and their overall durability. Harsh environments can decrease the lifetime of a PV module below 25 years, which is the threshold lifetime suggested for all climates by most PV manufacturers. Crucially, this is also the expected period over which the cost of generated electricity is most often based yet has not been validated given the relative youth of the PV market. Reduction of the PV module lifetime through degradation and failures can significantly affect the financial and technical viability of solar PV as a source of clean electricity and more robust predictions of module lifetime are urgently required.
One very significant cause of failure is corrosion. Environmental moisture penetrates the PV laminates and reacts with the different polymers and metallic parts of the construction, accelerated by higher levels of temperature. From hydrolysis of the most commonly used encapsulant (Ethylene Vinyl Acetate, EVA), acetic acid is produced and attacks further the cell electrical contact metallisation, cell interconnection ribbons and back contact of the PV cells. Corrosion affects mainly the series resistance (Rs) of a PV module, causing severe decrease of the PV electrical power output, and is currently understood to be the second highest cause of energy yield loss of systems installed in the last 10 years.
The main areas requiring research have been identified as: determination of the temporal evolution of the distribution of moisture content within a PV module subjected to a given environment; full understanding of the chemical reactions taking place and separation of the impact of the different component degradation on the PV performance of a PV module; investigation of the corrosion impact on the performance of PV modules exposed to outdoor conditions, for a non-tropical climate.
The paths that the moisture follows within a PV module have been already investigated through theoretical simulations. However, these simulations currently lack rigorous experimental validation, that includes accurate values of moisture concentration accumulated within a PV module. To this end, a method that measures the equilibrium moisture content absorbed by the polymers contained in a PV module is applied, accompanied by a non-destructive method for the quantification of the moisture presence within a PV module. The values that result from the moisture measurements are used for verification of theoretical simulations implemented with COMSOL Multiphysics. Values of moisture concentration at different positions within a PV module are needed for understanding of the corrosion of the different metallic components contained in a PV module.
Published studies of the various mechanisms of corrosion of different components of a PV cell exist but stop short of relating this to power output. This is addressed here, in which a method that separates the impact of each mechanism on the degradation of the electrical power output is presented, thus allowing prediction of specific failure modes for a given bill of materials and operating environment. Half encapsulated PV cells (with either front or rear side exposed) are immersed in acetic acid baths or stored in an environment of high level of relative humidity and temperature (damp heat conditions). The results are compared to the findings of fully encapsulated PV modules aged under the same damp heat (DH) conditions. Both electrical and material characterisation are involved for identification of the different mechanisms. Results show that the most severe degradation is caused by accumulation of acetic acid on the front side of the solar cells. Although aluminium reacts severely with moisture, the aluminium back contact corrosion was found to be a negligible failure mode for fully encapsulated PV modules. Additionally, the impact of different back sheets on corrosion is studied, which again seems to be negligible, as the moisture accumulated at the front side of a PV cell is mainly affected by the diffusion coefficient of the encapsulant.
Finally, the impact of corrosion on PV modules installed in the field is poorly addressed in current literature, especially for PV modules exposed to non-tropical climates. The simulations available are not based on the physics of the degradation mode, but are empirical relationships whose parameters are extracted by fitting to indoor performance data. This approach makes these methods unreliable for outdoor predictions. Moreover, they are not validated against real outdoor data. The research in this work has achieved a method to partially understand this effect, as it is very difficult to separate the electrical signatures of different failure modes that occur simultaneously. The method involves the estimation of the series resistance evolution of PV modules operating at Loughborough University for 7 years, combined with visual inspection. The results show that seven years is a short period to observe significant corrosion in a temperate climate, but the method applied is adequate for its detection.
... via Finite Element Analysis (FEA) for the prediction of the moisture content in the laminate structures based on the Fickian diffusion model [7][8][9]. A more accurate model based on FEA using dual moisture transport mechanisms has been recently developed for different encapsulation materials [10]. ...
In den letzten Jahren häufen sich Meldungen über Probleme bei Polymerfolien in PV
Modulen. Die Ursachen hierfür sind oftmals nicht ersichtlich können aus in
unangemessenen Materialien, Qualitätsschwankungen in der Folienproduktion oder
Prozessschwankungen in der Modulfertigung begründet sein. Um derartige Probleme
in der Zukunft zu minimieren, bedarf es einem verbesserten Verständnis der
Materialzuverlässigkeit, um im Idealfall Fehlervorhersagen treffen zu können. Dieser
Beitrag erarbeitet die Datenbedarfe für derartige Forschung. Für die Forschung an
Materialzuverlässigkeit für PV Modulen benötigt man Daten in verschiedenen
Kategorien. Die notwendigen Kategorien untergliedern sich in Detailinformationen zu
Komponenten, dem Bauteil und der Anlage, den Einsatzbedingungen und dem
Standort, sowie den damit zusammenhängenden Klimadaten. Für die
Zuverlässigkeitsbetrachtungen ist der Verlauf der Eigenschaftsänderungen von
Komponenten und Materialien über einen größeren Zeithorizont und
unterschiedlicher Klimate von elementarem Interesse. Durch die komplexer
werdenden verwendeten Materialverbindungen ist eine detaillierte Erfassung
auftretender Degradationseffekte und der verbauten Bill of Material (BOM) wichtig,
um die Qualität zu sichern, die Zuverlässigkeit im Betrieb zu bewerten und folglich
Handlungsempfehlungen abzuleiten. Dies ist das Ziel des Projektes ANOMALOUS.
Aus Messdaten an Polymeren von PV Modulen im Feld sollen aussagekräftige Daten
generiert werden und daraus eine Datenbasis für die Vorhersage von zuverlässigen
und an die Umwelt angepassten Materialkombinationen in hochqualitativen
Produkten zu schaffen.
