Search

36th European Photovoltaic Solar Energy Conference and Exhibition; 977-982, Power output results of module measurements performed in independent laboratories often appear lower than those indicated on the label. The reason for this effect is that several factors that may affect a PV module’s power output, are not taken into account. PV modules made of crystalline silicon solar cells suffer an initial slight loss in peak power, an effect known as “light induced power stabilization” [1,2]. Many module producers know this effect and have this light induced degradation (LID) included in their product guarantee. Before starting the IEC reliability tests, PV modules need to show a stable output. Which is why they must be exposed to sunlight or a solar simulator at over 20kWh/m2. This power stabilization test is also compulsory according to the IEC 61215 standard on certification of photovoltaic modules [3]. When different combinations of module materials are tested for durability in, for instance, damp heat (DH) and thermal cycle (TC) testing, stable solar cells are needed as a reference to distinguish between the various effects of the materials. In the performed experiments, durability testing results with and without light soaking (40kWh) were compared.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1207-1211, To avoid long time failures of PV power plants, reliability testing and modeling of novel photovoltaic (PV) material combinations has gained importance within the last years. In this work, conducted within the research project ADVANCE!, we present an image based deep learning approach to extract degradation-relevant information from aged PV modules. The basis of the work is a comprehensive database, established within the project INFINITY, which includes extensive time-resolved measurement and characterization data of aged PV modules, that have been subjected to precisely defined accelerated aging scenarios. Within this work, electroluminescence images serve as input for the development and application of a deep learning approach to extract degradation parameters. For defect classification and localization, we use a Mask R-CNN architecture, which allows instance-level segmentation and classification in parallel. The extracted information can be used for subsequent statistical analysis, where additional information is available, to make predictions about the operational lifetime of a module under different climatic conditions. Although the amount of data is comparatively small and the distribution of the defect classes within the dataset is not uniform, the available results show the potential of our approach.

38th European Photovoltaic Solar Energy Conference and Exhibition; 1193-1195, Photovoltaic systems can be controlled with several approaches. By means of monitoring or with sample measurements on site. On a 9-year-old photovoltaic system with 970 kWp in the south of Austria, both approaches were pursued to investigate whether a cost-effective monitoring analysis alone is sufficient. The identification and partial repair of several superimposed failure cases such as shading, dirt, glass breakage and backsheet cracks ultimately showed that a data analysis with a determined performance ratio alone is not sufficient to draw complete conclusions about PV system and energy yield.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1553-1556, Operation and maintenance companies, PV plant owners and scientific PV institutes have the challenge to monitor PV installations correctly. When a changed performance ratio is recognized, it is to clarify whether the installation or the sensor is wrong. To be sure that solar irradiation sensors for photovoltaic applications are accurate, a cross-check is applied for four different application cases in the laboratory and in the field. These examples include comparisons between measurement devices like a pyranometer, silicon solar cell irradiation sensors or a photodiode sensor. In the end, guidelines for reliable measurements in the field are provided.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1536-1541, Detecting failures in a PV plant is of vital importance for the productivity and can largely be done by analyzing the data recorded from various sensors. To increase the reliability of such methods, there is a need for an automatized procedure able to identify suspicious PV plants that could be further investigated with other more costly and accurate methods. This motivation has led to the definition of a statistical approach for evaluating the status of the plant through the years that can detect long-term failures in a PV plant. In this paper, the proposed approach is defined, elaborated and qualitatively verified. A set of PV plants were inspected using the proposed method. The results and observations show the potential of the developed method for evaluating PV plants for operation and maintenance purposes.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1076-1078, Bifacial solar panels on industrial roofs are a viable option to boost the annual yield. Because of the strong influence of albedo, the yield of bifacial PV installations is difficult to simulate and predict. To evaluate the long-term benefits of bifacial solar panels and possible effects of albedo changes, 20 modules including dummies were installed on a white-painted industrial flat roof using a bifacial PV module supporting construction. The daily yield per module was measured using previous checked power optimizers and the data received by the monitoring portal was evaluated over one year. For the investigated setup, it was found that a benefit of around 17 % for the east and 14 % for the west orientated bifacial modules over monofacial modules was obtained at the beginning. After one year of operation, the benefit had reduced to around 7 % for the east and 5 % for the west orientated panel, due to moos growth combined with pollution, resulting in an albedo loss.

37th European Photovoltaic Solar Energy Conference and Exhibition; 904-907, According to latest studies, cell and interconnection failures are to most common ones besides backsheet and encapsulation issues in PV modules. Solder joints within the module, which are not meeting the target quality, often lead to major issues after aging, comprising burn marks, hotspots, arcing discharges and of course substantial power losses. Besides security and safety issues, such age-related effects can lead to major financial losses for manufacturers, investors and plant owners. Within the Austrian flagship project “Sustainable Photovoltaics”, a nondestructive method was developed for analyzing the quality of solder joints in PV modules (on site & in production line) using a multi frequency eddy current approach. With the presented solution the conductivity of each solder joint can be analyzed, enabling the possibility of early failure detection, and hence initiating possible repair approaches. Measurement results show that the calculated state or conductivity decrease of aged solder joints can be successfully correlated to electroluminescence (EL) images. This enables a solder joint quality analysis without, unlike EL, directly powering the PV module.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1042-1044, The quality of ethylene vinyl acetate (EVA) as encapsulation material for photovoltaic modules is of key importance for the long-term durability and performance of PV modules. The relevant factor for characterising EVA is the degree of crosslinking which is usually determined using the Soxhlet extraction method. Previous studies have already proven that Raman spectroscopy is suited as a decent alternative, as it is a non-destructive method to measure the degree of crosslinking in a significant faster way [1,2]. Within the international research project RETINA, Raman spectroscopy was used to determine the dependency of the degree of crosslinking on the main parameters of the lamination process: i) temperature, ii) pressure and iii) crosslinking-time. The major goal was to analyse the degree of crosslinking dependant on the depth of the encapsulant, i.e. studying potential 3D crosslinking effects, which is possible by utilising focus-variations of the Raman system. For that purpose a set of samples (mini PV-modules as well as pure-polymer laminates) was manufactured using specific crosslinking parameters.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1117-1120, Bifacial PV modules with their ability to use light on both sides of the solar cells offer a great potential for significantly increase the energy yield of PV. Despite the bifacial technology has established itself over the last years, a standardized characterization within the PV industry is still lacking, nevertheless the standard IEC TS 609041-2:2019 is already published. The goal of this research work is to utilize industrial equipment on-site as well as customized, relatively simple (fast and easy handling) characterization tools for repetitive measurements of the flash tester and furthermore bifacial modules in an industrial environment. Here, the focus is to follow the expectations defined by the standard, despite alternative methods and tools are used. In a first step, the flash tester as well as three sets of bifacial modules (different design/layout and cell types) were analyzed. In the future, a comparison with outdoor performance measurements and accredited laboratories will be conducted.

36th European Photovoltaic Solar Energy Conference and Exhibition; 991-994, Bifacial crystalline silicon PV modules have the advantage to produce energy not only with one side, but with help of a transparent backside with both sides. A market research showed that some bifacial PV modules are not fully optimized although scientific knowledge was available before. Some experiments based on six-cell mini-module were performed to analyze the feasibility for an adaption on standard 60-cell modules. Made changings and improvements on 60-cell panels were proved with an industrial flash test system. Finally, the alignment to a commercial supporting construction and finalization of the complete test set-up on a white painted industrial roof was successful.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1012-1014, Today there exists a growing market for biface modules. Compared to conventional modules, in which the solar cells are embedded between glass and a white back sheet, the cells are embedded normally between two glass panes. Due to the transparent backside reflected light can be used to increase energy yield. In order to stand out from the crowd and generate a competitive advantage for the company, various methods are already in use to optimize the energy yield. The aim of the current project is to increase the energy yield by using light guiding structured foils, glued to the back of a bifacial module. This paper first describes the concept of light management and the measurement concept for the study. The main part comprises the construction of one of the two used validation systems. Furthermore, reference measurements and bonding tests are presented.

35th European Photovoltaic Solar Energy Conference and Exhibition; 2018-2020, Large knowledge about failure possibilities of PV plants has been accumulated during the research Project INFINITY. This paper intends to develop tools for optimising the maintenance strategies of PV systems. The developed software, presented in this article, provides a tool for responsible people to overcome the lack of expert knowledge in that area in a way to enable them to find these potential failures. It represents a support for laypersons as well as professionals.

35th European Photovoltaic Solar Energy Conference and Exhibition; 75-78, Crystalline silicon PV modules are normally manufactured with lead-coated interconnectors in a soldering process. Due to the significant improvement of electronic conductive adhesives (ECA) in the last years, the interconnection of silicon solar cells by gluing has become possible as well. This young technology could help fulfil the European directive RoHS without exceptions and avoid lead in interconnectors and components in PV modules. Furthermore, the gluing concept is ideal for high efficiency solar cell technologies that cannot deal with high soldering temperatures. Scientific investigations of standard soldered solar cells and glued ones were done at laboratory and outdoor test platforms. Reliability and economic issues were taken into account. Finally, a 5 kWp PV plant consisting of 20 panels was manufactured and built for demonstration purposes.

RET.Con 2018: Tagungsband : 1. Regenerative Energietechnik-Konferenz in Nordhausen 8.-9. Februar 2018, p. 103

35th European Photovoltaic Solar Energy Conference and Exhibition; 1284-1286, Within this work miniature digital temperature sensors were utilized to monitor the moisture ingress in a specially prepared photovoltaic mini module during accelerated aging. This work was conducted within the Austrian flagship project INFINTIY, which deals with the development of climate-adapted PV solutions in order to achieve yield-optimized PV systems with extended system lifetimes. As a further step in conducting research related to moisture ingress in PV modules, within this work a mini PV module was manufactured, comprising eight digital temperature and humidity sensors in front and behind a solar cell (substituted by an aluminium sheet). The goal here was to determine the diffusion path of the humidity diffusing through the backsheet to the front side (sunny side) of the laminate. Here it was essential to gain knowledge about the duration of the moisture ingress to the front part of the test module during accelerated aging as elevated humidity causes corrosion effects on e.g. the grid fingers (reduced electrical conductivity).

35th European Photovoltaic Solar Energy Conference and Exhibition; 1385-1389, Microclimatic conditions inside of the enclosures of photovoltaic (PV) inverters are suspected to have a tremendous impact on degradation and failure modes of the devices. To address this issue, a custom multi-channel data logger has been designed which is capable of continuously measuring temperature, relative humidity and wetness in confined space. The collected data is written to a flash memory and additionally sent to a server via GSM to enable remote real-time monitoring. Consequently, the instrument is designed to be integrated in a PV inverter and to be utilised for the characterisation of the respective microclimatic conditions and the identification of error sources, where required. Preliminary field test results showed that the ambient conditions inside of an inverter are rather dependent on its duty than on environmental situations. The findings can be useful to optimise the design of PV inverters and their enclosures and hence contribute to an increased durability and a prolonged life-time.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1937-1939, A power plant in the south of Austria built with multi-crystalline PV modules was investigated after a hail storm. Standard measurement techniques like thermography, electroluminescence and ultraviolet fluorescence were used. It was found out that glass broken modules were not only responsible for a loss in power and yield. The remaining good-looking modules had invisible to the eyes cell damages causing the loss. Because of these impressive findings, the insurance decided subsequently to change the most affected bad working modules.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1709-1712, A series of test-modules – intact and with deliberately generated failures (micro-cracks, cell-cracks, glass breakage and soldering defects) - were exposed to various stress conditions (temperature, humidity and irradiation) in order to see the stress-induced effects and potential propagation of the failures on the performance. The modules were thoroughly electrically characterized before and after the accelerated ageing and outdoor tests by electroluminescence and IV-curve measurements. In addition, the test-modules were subjected to time resolved characterisation during the ageing tests by UV-fluorescence imaging. The induction period for the fluorescence effects of the polymeric encapsulant to show up and the characteristic fluorescence patterns formed upon damp-heat storage, irradiation and outdoor exposure were analysed in detail. The effect of cell-cracks and glass breakage on the local extinction of the fluorescence is discussed.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2291-2294, Different sized power plants with crystalline silicon PV modules were inspected directly on-site. For the inspection purpose, measurement equipment was used in different situations. First at plants with good infrastructure and accessible power sockets for powering whole PV strings, second with only a small battery powered system for powering separate modules. Characterization methods like thermography, electroluminescence and ultraviolet fluorescence were performed for field use with the goal of testing the practicability in a non-laboratory surrounding. The checked PV plants of different sizes were evaluated to accessibility and difficulties faced by the local conditions on-site. In the majority of cases, and despite of adverse conditions, the checks were successfully performed.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1713-1715, Within this work miniature digital temperature sensors were utilized to monitor the moisture ingress in photovoltaic modules during accelerated aging. The investigated modules were developed within the research project PV@Façade, which deals with the integration of PV modules in the building envelope to obtain long-term resistant multi-material composites. Hence, eleven samples, varying in manufacturing procedure, material composition and/or material supplier were analyzed while stored under damp-heat conditions (85°C, 85 % r.H.). As expected, the glass-glass setup with edge sealing performed best in regard to moisture resistance. For the non-glass modules, samples using TPO as encapsulation material showed good results. Nevertheless it was found, that already small differences in the distance of the sensor to the module edge of the different samples strongly influence the outcome of this experiment.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1779-1783, Even though ethylene vinyl-acetate (EVA) is for more than 30 years employed as an encapsulating material it has some major drawbacks like formation of acetic acid during aging and the peroxide-initiated chemical crosslinking during module lamination. In several studies, the origin of EVA degradation has been linked to its composition and interactions at its interfaces with other PV module components (additives formulation, formation and permeation of acetic acid and residual peroxides). However, PV module degradation was found not only dependent on external stress factors like UV, temperature and humidity but also on internal stress factors like material composition (e.g. additives) and material combinations (e.g. encapsulant-backsheet combination). So far only few studies have looked on influence of internal factors on degradation of PV modules. The main purpose of this work was to understand the role of the encapsulant composition on the degradation behavior of PV modules due to interactions at interfaces of PV components under different stress conditions. Once the mechanisms behind PV module degradation are understood better, it is possible to optimize PV modules for different operating conditions.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2370-2374, The Austrian national project INFINITY focuses on design improvements for PV system components operating in different climatic regions. This topic appeared increasingly often in the past Photovoltaic conferences, being a result from globalization of the PV industry and market, where the same components are mounted under different environmental stress. In this context the initial target of the project was to gather failure data from PV installations in various climate zones, mostly from literature and cooperation like the IEA PVPS Task 13. A standardized data input was achieved by using an extended format of the IEA PVPS Task13 failure survey, allowing to enter PV system and failure information in rich detail. The component’s structure and failure structure was elaborated by combining input from reliability workshop proceedings, Task13 and experience in Photovoltaic reliability testing. This structure was further mapped to a database to collect and prepare the input for further statistical analysis. This paper presents the results from comparing different climate zones in the frequency of failures from 1970 until now. From this already some differences can be seen between the different climate zones.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2295-2298, When it comes to the reliability of PV modules it is important to guarantee a constant energy yield while at the same time achieving a low failure rate of the modules. Amongst the numerous environmental influences that increase the risk of failures in PV systems, it is assumed that the different climate zones play an important role. This works deals with analyzing the issue of deterioration of the energy yield of PV systems by using logistic regression models. It will be shown that the risk for such power losses is higher in climate zones that include extreme conditions, e.g. high temperatures and snow loads and hence, a clear connection between failures that result in power losses and the different climate zones can be made.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 123-126, With the current trend in the photovoltaic industry towards thinner solar cells and four (or more) busbar modules, the cell-interconnection/stringing process is becoming more challenging. Besides the possibility of damaging solar cells during the soldering process itself, thermal and mechanical stresses within this process step are also assumed to induce cracks, which are occurring later during the operation of the PV module under certain environmental conditions, such as heavy snow or wind loads and excessive temperature fluctuations. In order to produce reliable high-quality PV modules at sound costs, it is necessary to minimize the stress on the solar cells during the manufacturing process. Within this study Raman spectroscopy is utilized to analyze the stress of solar cells induced by the interconnection process. Besides investigations on manually soldered solar cells, also industrially interconnected solar cells were evaluated. Here, an industrial soldering as well as a glueing/bonding interconnection technique was analyzed. All investigated solar cells are based on three busbars technology.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1969-1972, During this work a portable solar cell characterization device as well as its application in a building integrated photovoltaic (BIPV) test system is shown. The solar cells are characterized by measuring their currentvoltage curve (I-V-curve) in user-defined intervals. A test setup was build that allows the application of various types of façade elements and solar cells. Up to four solar cells, oriented at the four cardinal directions, can be measured simultaneously over a whole day, which allows a comprehensive comparison of them. Besides additional energy yields also advantages of a more consistent/user adapted energy distribution over a day, resulting from façademounted solar cells/modules, can be evaluated. To enable a more detailed data analysis the local irradiance as well as the temperature of each cell and the specific façade panel is determined. Outdoor measurements under the influence of natural sunlight and various weather conditions were conducted with crystalline cells and thin film (CZTS) modules, mounted on exchangeable façade elements.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 786-790, Different busbar concepts with three, four, five and six busbars (BB) on standard silicon solar cells on both full cell format (156 mm x 156 mm) and half-cell format (156 mm x 78 mm) were investigated. 40 prepared single-cell mini module specimens, five of each per variation, were tested with a flash cell tester to determine series resistance and maximum power for a relative comparison. Simulations with original measured parameters were compared to the determined values of the experiment. A dependency was found between the number of busbars and the finger grid design, all together affecting series resistance and efficiency. An optimized busbar concept with at least 4-BB technology is recommended as a first step due to performance improvement and economic issues.

31st European Photovoltaic Solar Energy Conference and Exhibition; 160-163, Solar cells are composites of several materials. Due to this fact, the materials will determine the internal stresses of the cell. This paper considers one aspect of solar cell construction: the addition of conduction ribbons to the silicon surface of the cell. We use Raman spectroscopy to measure the stresses present in the silicon substrate, before and after the ribbons have been applied. We also consider comparing two methods of application: traditional soldering and a novel gluing method. Both methods significantly increased the stresses present, remarkably, by similar amounts. We conclude that the major source of stress is the ribbon itself; the type of adhesion method made little or no difference when measured with Raman spectroscopy.

31st European Photovoltaic Solar Energy Conference and Exhibition; 2430-2434, Raman spectroscopy is proposed as a fully versatile, industrially applicable in-line quality control method for measuring the degree of curing of elastomeric ethylene vinyl acetate (EVA). As a purely optical method, Raman spectroscopy enables a contact-free, non-destructive analysis e.g. through the front glass. The characteristic Raman spectra of differently crosslinked EVA show subtle but characteristic spectral differences in the CH-stretching vibration region (3.000 – 2.800 cm-1) that correlates unambiguously and reliably to the state of encapsulant crosslinking. An external calibration against standard Soxhlet extraction is still necessary, but only once for each material type. In an initial proof-of-principle phase, various EVA samples were analysed with a Raman laboratory system, both as bare EVA foils and in assembled glass-backsheet and glass-glass modules. Subsequently, an industrial Raman demonstrator was designed, built and applied to the same samples. A detailed evaluation of the results proved good analytical quality at analysis times down to 0.1 s per point. Finally, the device was installed and successfully operated in a PV module manufacturing line. Raman spectroscopy has thus proven its capability for contact-free multi-point real-time analysis of PV modules in-line in the manufacturing line.

31st European Photovoltaic Solar Energy Conference and Exhibition; 938-943, One of the current research challenges in photovoltaics is the optimization of the solar cell grid finger metallization and the enhancement of the efficiency itself. At the moment, standard silicon solar cells use a linear, uniform grid for the power dissipation. Within this work, an alternative, nature inspired metallization structure was developed, utilizing an evolutionary algorithm for the design optimization. Here, the main research goals are the reduction of the shading caused by the front metallization, as well as an enhancement of the power output of the solar cell. For the creation of an alternative metallization structure, possible nature inspired designs are investigated and evaluated, in terms of usefulness for solar cell metallization application. Here, leaf venation systems and river deltas with its branching tributaries served as major inspiration sources. Resulting from these inspirations, a randomly branching structure was developed, utilizing a so called minimal spanning tree for a randomly generated set of nodes. To optimize this nature inspired branching structure, furthermore an evolutionary algorithm was applied for improving the spatial distribution of the pattern. For the validation of the design, electrical solar cell simulations were carried out. In addition, solar cell prototypes were manufactured, utilizing two alternative metallization approaches, inkjet printing and electroplating. Because of minimizing the line width, realized with the help of the alternative metallization approaches, as well as applying the developed bionic design, a reduction of the metal amount of the front metallization and therefore a minimization of the front shading is feasible.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3133-3137, The serious pricing pressure in the manufacturing of photovoltaic (PV) modules causes an immediate need for a reduction of production costs. The time limiting process in PV manufacturing lines is the lamination process. Today, the predominately used embedding material in PV modules is ethylene vinyl acetate (EVA), which needs to undergo a crosslinking step during the lamination process in order to achieve the required polymer properties. Investigations on the thermo-mechanical properties of EVA with dynamic mechanical analysis (DMA) showed that already at much shorter crosslinking times than usually used stable values can be achieved. Due to these findings, the request to reduce the lamination time arises. Therefore the long time performance of mini-modules manufactured at different lamination times (1, 3, 5 and 10 min. crosslinking time) stored under various ageing conditions (accelerated under damp heat (DH) conditions with or without irradiation, on the roof and in the dark) was investigated. Besides the monitoring of visual changes, the degree of crosslinking was evaluated non-destructively by Raman spectroscopy to trace the post-processes initiated by the various ageing treatments.

29th European Photovoltaic Solar Energy Conference and Exhibition; 161-164, One way to increase module efficiency is to use deep structured ribbons as cell connectors in photovoltaic modules. The conventional soldered, flat ribbon connector is replaced with a glued, deep structured ribbon. When light strikes a cell it is reflected at the ribbons and, in a conventional cell, lost. The structured ribbons and the glass/air interface redirect some of this light back to the cell. In this paper we compare the yield of conventional photovoltaic modules with soldered flat and glued flat connector ribbons to glued deep structured ribbons, both under laboratory conditions and in field. We found that the new design increases short circuit current by 2 % and yield by 1.5 %. To analyse this effect in detail, simulations are conducted that confirm the experimental findings.

29th European Photovoltaic Solar Energy Conference and Exhibition; 171-176, The aim of this work was to analyze new module concepts and their influence on the electrical power output. Alternative methods for the soldering of interconnections between solar cell busbars and solar cell tabs, the replacement of standard flat ribbons by means of innovative grooved connection wires and the use of new developed encapsulations were investigated and characterized. One emerging possibility to overcome the shortcomings of soldering is the use of electrically conductive adhesives. Conductive adhesives have many advantages: 1, toxic heavy metals such as lead are not required. 2, no tin solder is necessary. 3, fewer cracks are arising during the interconnection process and 4, good electrical conductivity and sufficient mechanical bonding between rough surfaces can be achieved. By replacing of a standard flat ribbon by a grooved solar cell interconnect wire or Light Capturing Ribbon (LCR) an increase of the efficiency of a solar module is expected by reflecting more light back onto the surface of the solar cell (see Fig.1: LCR). New thermoplastic materials allow a faster and cheaper production process, a reduced moisture permeability and a higher UV-transmission.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3360-3363, Over the last years potential induced degradation (PID) occurred on several photovoltaic (PV) power plants and therefore increased interest in researching this phenomenon. It is known that PID occurs when certain material combinations coincide with a high negative potential between the solar cells and frame of the module. Furthermore the degradation depends mainly on the migration of sodium ions into the surface of the solar cell, driven by the high potential difference. In this investigation, the mechanisms inducing PID were simulated in detail and compared to experimental measurements. It can be shown that the electric fields originating from the potential differences are promoting an ion transport from the glass towards the cells. As a new avoidance strategy and to verify the predicted reason of the ion transport, a so called “guard ring” was installed at PV modules. Properly positioned, this thin copper wire can reduce the effective electric field strengths and thus the PID effect to about one fifth of its original value.

29th European Photovoltaic Solar Energy Conference and Exhibition; 2457-2461, Ethylene vinyl acetate (EVA) is the dominating material for the encapsulation of solar cells. During Photovoltaic (PV) module lamination a three dimensional network is formed by chemical cross-linking of the polymer chains in order to increase the thermal stability of the material and prevent the material from melting within application relevant temperatures up to 100 °C. The crosslinking reaction is the time-determining step of PV module lamination, which is discontinuous and can take up to 30min, depending on the EVA type. A better understanding of the reaction kinetics, especially at the beginning of PV module lamination, could lead to promising approaches for shortening of PV module lamination times but also for optimization of the EVA formulation. Therefore, the main aim of this study is to investigate the cross-linking behavior of EVA during PV module lamination. Three commercially available EVA encapsulation films with different stages of crosslinking were prepared for the investigations. The specimens were then investigated by Soxhlet extraction, Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and tensile tests and a corresponding degree of cross-linking was derived for every method. As expected, every method revealed different reaction kinetics as well as varying sensitivities were observed. These differences can be explained by the typical scheme of radical chain reactions. At first, radicals are formed by the decomposition of the peroxides, which can be seen by DSC, followed by the formation of polymer radicals. In the next step, the polymer radicals react with each other or other polymer chains, and long chain branched polymers are formed. Although having increased molecular mass, the long-chain branched polymer molecules are still soluble and therefore cannot be detected by Soxhlet extraction. Also tensile test does not show any significant changes within the first three minutes of PV module lamination. The post-yield behavior of the material is highly influenced by the cross-linking density of the material. Comparable to Soxhlet extraction after 3 minutes a steady increase in stress level at 800 % strain was observed, which indicates the starting formation of a 3-dimensional network. The most sensitive method to describe the initial stages of cross-linking proved to be DMA, where any slight change in the molecular mass can be seen instantly. Already after 5 minutes of cross-linking time no significant changes in the thermo-mechanical properties were observed anymore. Furthermore, the measured modulus curves indicate the elastomeric character of the material, with no significant decrease of modulus after 65°C due to melting of the material. It can be concluded that a sufficient 3-dimensional cross-linking network was formed, even though only about a third of the initial peroxide has reacted up to this time. Currently, a degree of cross-linking higher than 70% obtained from Soxhlet extraction, is used as quality control standard in PV industry. Thermo-mechanical properties of the investigated EVA films demonstrate a sufficient state of cross-linking already after 5 minutes, which corresponds to a Soxhlet value around 50%. Summing up, a significant reduction of lamination time up to 5 minutes seems viable. Nevertheless, the effect of the remaining, still reactive peroxide under service relevant conditions cannot be neglected.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3115-3118, In a state-of-the-art photovoltaic module the solar cell area accounts for about 85 to 90% of the total module area. The rest of the module area is dominated by the back-sheet. Light impinging onto the back-sheets is mostly reflected and a part of the reflected light is re-directed onto the solar cells. This photon recycling effect is well known, but the efficiency of this process is not well understood until now. In this paper we present the results of a study on the photon-recycling efficiency of different ISOVOLTAIC back-sheets and investigate the reasons for their varying optical performances. A series of mono-cell-modules with different back-sheets was manufactured and carefully investigated under Standard Test Conditions and by applying the Laser Beam Induced Current method. In addition, the scattering properties of the back-sheets were measured which are the basis for the modelling of the photon recycling efficiency. The experimental as well as the modelling results show good agreement. In particular it is shown the photon recycling efficiency within a module significantly depends on the type of back-sheet used. The average photon recycling efficiency of a typical module boarder region is found to range from about 19 to 23%, depending on the type of back-sheet used.

29th European Photovoltaic Solar Energy Conference and Exhibition; 3334-3338, PID (Potential Induced Degradation) is one of the severest degradation mechanisms the photovoltaic industry of crystalline and multicrystalline modules faces today. It depends mainly on the travelling of Na+ ions, mainly concentrating in stacking faults causing electrical shunts. These shunts can be observed very precisely and give a view of the travelling and concentration of the ions over time of stress. In this paper the shunt development of different encapsulants during accelerated PID tests is investigated, and how it depends on the thickness of the encapsulant. The leakage current and the power loss are correlated with the electrical permittivity of the encapsulants.

28th European Photovoltaic Solar Energy Conference and Exhibition; 3020-3025, With the increasing use of PV installations and the highly competitive situation on the PV module market, the modules’ reliability and long-term performance over projected operational lifetimes of 25+ years become key factors. One component known to have a vital impact on the long-term characteristics, and hence of particular interest here, is the polymeric solar cell encapsulant. Presently, the prevalent material of choice for this is elastomeric ethylene vinyl acetate (EVA). While several analytical methods to evaluate the curing, i.e. crosslinking, state of EVA exist, an industrially applicable in-line quality control method is still lacking. The approach explored in this work uses Raman spectroscopy. In contrast to most other methods, Raman spectroscopy allows a contact-free analysis through the front glass, in-line and in real time in the manufacturing line. The Raman spectra of differently crosslinked EVA samples and modules show subtle but characteristic spectral differences in the CH-stretching vibration region (3.000 – 2.800 cm-1) that correlate unambiguously and reliably to the state of encapsulant crosslinking.

28th European Photovoltaic Solar Energy Conference and Exhibition; 3180-3183, Aiming at obtaining reliable values on power loss and gain in PV modules, this work systematically investigated the effective impact of both established PV technologies and newly suggested improvements in a number of different combinations. Using different measurement approaches, this systematic investigation was first done using single-cell mini-modules. Referencing against the power generated by the respective cell alone, the effects of the various manufacturing stages were analysed. The different PV module components - PV cell, ribbon, encapsulation material, glass and backsheet – were varied, including new approaches like light capturing glued ribbons (LCR™) and antireflection coated glasses. The results then were compared to full 60-cell modules, to both validate the results of the mini-module series and evaluate the effect of a multi-cell vs. a single-cell arrangement. Additionally the results were measured against plausibility calculations.

27th European Photovoltaic Solar Energy Conference and Exhibition; 3561-3565, A key factor for the long-term performance degradation of PV modules is an in-use damage of the actual solar cells by loads causing (micro-)cracks. Besides external mechanical forces, the main source of these is forces created by different thermal expansions of the module components, inducing mechanical loads as soon as the module temperature changes. These thermo-mechanical effects are complex and highly interdependent, also since they are not only affected by the momentary temperature situation but likewise by the module’s life history. This becomes an issue since manufacturing and use of PV modules necessarily comprise temperature changes; residual stresses thus become an inherent part of each module. To achieve a better understanding of these effects, resistant strain gauge rosettes and temperature sensors have been included in dedicated test mini-modules comprising only one solar cell each. Using these, the principal strains occurring during lamination and later in thermal cycles simulating use have been monitored and analysed. It can be shown that the thermal loads of the lamination process impose the highest stresses on the solar cells, and that this stress magnitude is not correlated to the lamination time. The experiments also confirm the protective effect of the ethylene/vinyl acetate (EVA) encapsulant for preventing cell fracture. Related simulations taking into account the highly temperature-dependent material properties of the EVA can qualitatively reproduce the experimental findings, although a detailed reproduction will requiring future efforts taking even more effects into account.