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The silver grid corrosion phenomenon of c-Si solar cells, often called “snail trails” or “snail tracks”, which occurs mainly shortly after installation of PV modules in the field, was first observed approximately one decade ago in the southern part of Europe. It was recognized quickly that these discolorations on the metal grid fingers are always accompanied by cell (micro) cracks. From the herein presented investigations, it can be shown that several different chemical mechanisms and material involvements can lead to the visual phenomenon of silver grid finger discoloration. It must therefore be clarified that the term “snail track” (or “snail trails”) only describes a failure class and not a single degradation mechanism. This work focuses on a bottom up approach, which includes the chemical analyses of the affected cell parts extracted from various industrial modules which have been installed in the field. In addition to the analytical investigations after field failure, the modules are exposed to artificial stresses to investigate the development, formation or further reaction of the snail track degradation products. Since the phenomenon is always accompanied by diffusion open areas in the module (cell gaps, cell cracks), the diffusion of reactant partners from the rear side of the module, e.g. atmospheric gases or additives from the back sheet material, has been the most suspected root cause from the beginning of the observation. The role of these reaction partners is therefore highlighted within the results. Four different snail track degradation products have been identified until now: Silver carbonate, silver sulfide, silver phosphate and silver acetate. Silver sulfide snail tracks were only found after damp-heat test (only artificially induced), all other types were found from field failed PV modules and respectively partially from stress tests. The different snail track types, materials and module components considered being involved and the formation mechanisms are presented in this work.

Polymeric collectors have been exposed on outdoor testing sites in three distinct climatic locations and the climatic loads and collector temperatures have been monitored by the minute. The obtained data was analyzed with focus on the frequency and extend of the thermal loads, which the different components of the collector were exposed to. As a result this data can be correlated to accelerated aging tests.

In the manufacturing process of a common solar module, crystalline silicon solar cells are interconnected by soldering. Copper-based interconnectors, coated with a solder alloy are soldered on both sides of the solar cells on the contact metallization. Subsequently, the solar cell strings are embedded in between two sheets of encapsulant, commonly ethylene-vinyl acetat (EVA), which itself attaches to a front glass and a back sheet during the lamination process. Thermomechanical stress, due to the mismatch of the coefficients of thermal expansion (CTE) of copper and silicon, causes bowing of a back-contact solar cell after the soldering process. Additionally, thermomechanical stress can result in the failure of solder joints. By adapting the mechanical properties of an interconnector, thermomechanical stress can be reduced. Shaping a straight wire with a round cross section to a wave-like form reduces its effective tensile mechanical properties and leads to changes of its effective electrical conductivity. This study investigates the mechanical and electrical properties of wave-shaped wires with different amplitudes, periods and diameters. In addition, microscopic imaging reveals the geometry and potential defects due to the shaping process. The influence of the shaping process on the yield limit of commercially available copper-based wires is determined. For this reason, an algorithm is designed that allows the automatic and precise determination of the yield limit of these interconnectors. In this study, a maximum yield limit reduction of 88.5% compared to a straight wire is found. Furthermore, the influence of the shaping process on the electrical resistance is analyzed. For this purpose, the influence of wire damaging due to the shaping process, as well as the wires longitudinal length change is determined. An increase of the electrical resistance between 3.5% and 82.7% is measured. To choose an optimal interconnection concept for solar cells, the mechanical, as well as the electrical properties of the interconnectors have to be considered. This study correlates the advantageous longitudinal softness of wave-shaped wires, which potentially leads to a significant decrease of the thermomechanical stress in solar cells and of the bowing of back-contact solar cells, with the disadvantageous increase of the electrical resistance caused by the shaping process. The findings enable an optimization of a wire-based interconnection concept for back-contact solar cells.

Varying spectral irradiance affects performance of photovoltaic (PV) modules depending on their band gap and spectral response. Therefore, energy rating or yield prediction procedures should take into account the irradiance that is effectively available for a specific PV technology. This effective irradiance differs from broadband solar resource information first due to the different spectral sensitivity of PV devices and pyranometers, and second due to the difference between real and reference spectral distribution. The combined difference, also referred to as ‘spectral impact’, is to date considered in form of fixed spectral gain or loss factors applied to the broadband solar resource – if it is considered at all. Values for the monthly or annual spectral impact have been reported for several locations; however without estimates of their uncertainty. This article addresses the question of how large the uncertainty of the spectral impact is. Contributions to the uncertainty of the spectral impact are discussed, with focus on the method of determining the spectral impact by means of measured spectral irradiance and calculated spectral mismatch factor ( MM ). Using a simplified procedure, the uncertainty of spectral impact was estimated from the average spectral mismatch uncertainty. It was found to be of the same magnitude as the spectral impact itself, and dependent on the PV technology. For five single-junction PV technologies, amorphous silicon, cadmium telluride, standard crystalline silicon, high-efficiency crystalline silicon and a wide-band-gap CIGS technology, the estimated uncertainty values were 1.8%, 1.4%, 0.9%, 1.0% and 1.2%, respectively. The results were obtained from a specific measurement campaign conducted from 01.06.2010 to 31.12.2013 in Freiburg im Breisgau, Germany, but the order of magnitude is considered to be typical. In order to validate the simplified uncertainty estimation method, a sensitivity analysis was carried out to evaluate the influences of calibration and drift of the spectroradiometer, high-angle-of-incidence conditions, the available wavelength range of the spectroradiometer and results obtained with different spectroradiometers. With the smaller wavelength range of 350–1050 nm, which is a typical range for various instruments used in many scientific publications, the calculated spectral impact was significantly smaller. The other influences were found to affect the result only within the estimated uncertainty limits. The uncertainty values presented here should be considered lower limits until they are backed up by further analysis.

Despite having generally excellent corrosion resistance copper is still susceptible to several forms of corrosion. To obtain accurate and current information about atmospheric corrosion of copper in Europe, two different approaches are implemented. The copper corrosion is assessed at 17 European test sites with different climates after 1 year exposure to weathering. These results are tested against to other available international corrosion datasets and the effects of different environmental parameters on corrosion are discussed. In a second approach, GIS-based spatial modelling of atmospheric corrosion for Europe according to the corrosivity function from ISO 9223/2012 is performed and the modelled results compared with the measured results. Spatial modelling is also implemented to predict the future development of copper corrosion in Europe. Therefore, pollution and climatic scenarios dataset are integrated into the dose-response function for copper.

The microstructure and intermetallic phase growth in solder joints of photovoltaic modules are investigated because of their significance for interconnection reliability. Interconnector ribbons with Sn60Pb40, Sn62Pb36Ag2, Sn43Bi57, Sn41Bi57Ag2 and Sn91Zn9 are soldered on the front busbars of industrial crystalline silicon solar cells. Cross sections are inspected using microscopy, SEM and EDX. The interconnections are isothermally aged, whereas the intermetallic layer thickness is determined successively. The microstructural changes in the bonds are characterized. Grain coarsening, volume increase of intermetallic compounds, Sn-penetration into the metallization and growth of grain boundaries between the phases are found. The composition of the intermetallic phases within Sn91Zn9-bonds is discussed. A diffusion model is used to simulate the intermetallic layer growth after 3000 h at 85 °C and thermal cycling from −40 °C to 85 °C for 600 cycles. A prognosis of the phase growth within the photovoltaic module after 25 years at the location Freiburg in Germany is made. It is found that the Ag 3 Sn-phase using Sn43Bi57 extends to 6.6 µm after 3000 h at 85 °C as compared to 2.6 µm for Sn60Pb40. After 25 years in Freiburg the Ag 3 Sn-layer within Sn43Bi57 joints is predicted to be 2.4 µm whereas within Sn60Pb40-bonds only 2.2 µm.

This work deals with the simulation of water vapor ingress into wafer-based PV-modules for long-term exposure under different climatic conditions. Measured material parameters together with climatic data sets from four test sites (tropic, moderate, alpine, and arid) were used to calculate the water concentration inside of the encapsulant between solar cell and glass for a lifetime of 20 years. Two back-sheet materials (PET-based and PA-based) combined with EVA as encapsulant were used in respect to their influence on water ingress. The results show faster water ingress for warmer regions, but the highest concentrations were found for the moderate test site. The water ingress was additionally influenced by the used encapsulant and back-sheet combination. In particular the temperature dependency of the mass transfer, which differs from material to material, was the focus of this investigation.

Today's Photovoltaic module production is driven by cost. Due to its high conductivity and solderability the precious metal silver is used in standard solar cell production as base material for solder pads. The need for replacing the costly silver emerges in various PV metallization techniques On the rear side, these solder pads (busbars) locally prevent the formation of a back-surface-field (BSF) leading to a decrease in open-circuit voltage. We therefor aim at reducing the silver content in solar cells while maintaining the solderability. To face this challenge we developed an interconnection method based on ultra-sonic (US) soldering to contact the aluminum on standard crystalline silicon (c-Si) solar cells. The method consists of a two-step process where first a tin alloy is employed directly on the aluminum and second conventional interconnectors are soldered onto the applied tin alloy. We investigate the adhesion of five different metallization pastes on the solar cells and compare it to the adhesion of soldered interconnector ribbons with our two-step US-soldering method on these metallizations. We find the adhesion of the solder joints to be independent of the metallization/cell adhesion. Metallographic analyses reveal that the tin alloy forms a direct contact to the Al-Si-eutectic underneath the metallization during our US process. The measured adhesive forces range from 0.5 N/mm to 16 N/mm of the metallization/cell interface and from 1 N/mm to 2 N/mm for the US-solder joints. Additionally we manufactured a 16-cell module consisting of cells with US-soldered contacts on the Al-rear side and compare it to a conventional module. The IV-characteristics show less loss in FF from cell to module (CTM) for the US-soldered module.

PV modules that are sold on the worldwide market today have to pass the relevant IEC tests for certification. These tests are only a mark for a certain quality level, not a reliability test. Nevertheless, manufacturers of PV modules give performance guaranties of 20 to 25 years on their products, some even more. Therefore the question to be asked is: ‘How to survive 25+ years between the pole and the equator?’ or, seen from the other side: ‘Why do PV modules fail?’ To answer this important question we will show a global approach, starting with the presentation of general failure reasons. On the one hand, extrinsic PV module failures can be caused by different climatic stress factors and by defective installations. In the following, we will show a classification of those factors, which provides the basis for weathering analyses in the lab. With this data background some major failures and related test methods will be presented. On the other hand, intrinsic failure reasons are to be taken into account. We will exemplify some intrinsic failure reasons on material level. Also, an overview of major failures and their frequency detected during certification will be presented in order to arrive at an assumption as to why modules fail. Finally we will explain adequate test methods to detect and measure the relevant failure factors and to test new materials, components and modules for future photovoltaic systems.

The peel test of soldered/glued ribbons on solar cell metallizations is the critical test in the PV industry and research community to qualify the integrability of cells into modules. It has been shown that the peeling angle of the test setup strongly influences the measured peel forces [1,2], leading to higher forces for decreasing peeling angles < 90& and weakest forces for 135&. Here, we apply the theory of Kinloch and Kawashita [3,4] to determine the adhesive fracture energies GA from 180& peel tests of three different ribbons which differ in compliance (softness) and thickness. The experiments show that the soft ribbon (sy = 62MPa) gives lower peel forces than the stiff ribbons (sy = 99MPa) while the adhesive fracture energies are higher. The thickness variation from 150 mm to 200 mm of the hard ribbon has no significant effect on the adhesive energy. Furthermore, our investigation confirms that switching from 90& peeling angles to 180& helps to reduce silicon fracture patterns at high forces. In conclusion, the adhesion does not only depend on the surface properties of cell metallization schemes and soldering conditions, but also on the choice of ribbon used for the peel test. We therefore recommend to use the adhesive fracture energy GA instead of the normalized peel forces to improve the consistency and comparability between different peel testing setups and ribbon materials as the peel test is essential for accepting (or rejecting) novel metallization concepts (plating, metallization pastes) and interconnection technologies (low melting solder alloys, conductive adhesives).

The influence of mixed maritime atmosphere on the degradation of metallic components of exposed solar thermal collectors was studied. Corrosion measurements of standard metal samples (unalloyed carbon steel, zinc, copper and aluminum) were performed according to ISO 9226/1992 and ISO 9223/2012 with two different test set-ups; one in the open atmosphere, the other inside a commercial flat-plate thermal collector. Moreover, the influence of defined microclimatic conditions inside the thermal collector on the durability of different absorber surfaces was investigated. The results show extremely high corrosion rates in the open atmosphere for all exposed metals in contrast to the samples inside the solar thermal collector, where high corrosivity was only detected for amorphous metals. The results of optical measurements of the exposed absorber samples show a very good stability of the materials. Additionally, different analytical methods were used for the characterization of corrosion products. This information can be used for the optimization of accelerated aging tests for absorber materials with respect to corrosive environment and salt content.

To test reproducibility of a technical specification under development for potential-induced degradation (PID) and polarization, three crystalline silicon module types were distributed in five replicas each to five laboratories. Stress tests were performed in environmental chambers at 60 °C, 85% relative humidity, 96 h, and with module nameplate system voltage applied. Results from the modules tested indicate that the test protocol can discern susceptibility to PID according to the pass/fail criteria with acceptable consistency from lab to lab; however, areas for improvement are indicated to achieve better uniformity in temperature and humidity on the module surfaces. In the analysis of variance of the results, 6% of the variance was attributed to laboratory influence, 34% to module design, and 60% to variability in test results within a given design. Testing with the additional factor of illumination with ultraviolet light slowed or arrested the degradation. Testing at 25 °C with aluminum foil as the module ground was also examined for comparison. The foil, as tested, did not itself achieve consistent contact to ground at all surfaces, but methods to ensure more consistent grounding were found and proposed. The rates of degradation in each test are compared, and details affecting the rates are discussed.

Traditionally, for the planning and assessment of solar energy systems, the amount of solar radiation (sunlight) incident on the Earth's surface is assumed to be constant over the years. However, with changing climate and air pollution levels, solar resources may no longer be stable over time and undergo substantial decadal changes. Observational records covering the past decades confirm long-term changes in this quantity. Here we examine how the latest generation of climate models used for the 5th IPCC report projects potential changes in surface solar radiation over the coming decades, and how this may affect, in combination with the expected greenhouse warming, solar power output from photovoltaic (PV) systems. For this purpose, projections up to the mid 21st century from 39 state of the art climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analysed globally and for selected key regions with major solar power production capacity. The large model ensemble allows to assess the degree of consistency of their projections. Models are largely consistent in the sign of the projected changes in solar radiation under cloud-free conditions as well as surface temperatures over most of the globe, while still reasonably consistent over a considerable part of the globe in the sign of changes in cloudiness and associated changes in solar radiation. A first order estimate of the impact of solar radiation and temperature changes on energy yields of PV systems under the RPC8.5 scenario indicates statistically significant decreases in PV outputs in large parts of the world, but notable exceptions with positive trends in large parts of Europe, South-East of North America and the South-East of China. Projected changes between 2006 and 2049 under the RCP8.5 scenario overall are on the order of 1%/decade for horizontal planes, but may be larger for tilted or tracked planes as well as on shorter (decadal) timescales.

Durability assessment of materials exposed to natural weathering requires accelerated testing for verification of the ultraviolet (UV) stability, especially for polymeric material. The type approval testing of photovoltaic (PV) modules according to the standards International Electrotechnical Commission (IEC) 61215 and IEC 61646 includes a so-called UV-preconditioning test with a total UV dose of 15kWh/m2 corresponding to natural weathering of about 3months only. A serious UV test representing the service life needs to apply a much stronger UV-intensity in a comparable way. Fraunhofer Institute for Solar Energy Systems performed an inter-laboratory comparison of UV-light sources in 13 accredited test labs and test centres of major PV module manufacturers. The most important topic was the spectral radiometric measurement of the used UV sources. Another main issue was the comparison with the integral measurements by the sensors used for control of the tests. Errors up to 120% were found.

In this paper the water uptake by PV-modules during weathering tests of the type approval standard IEC 61215 was simulated and compared with the water ingress under ambient outdoor conditions. For this purpose, the base materials, one encapsulant (EVA) and one back sheet (TPT), were analyzed regarding their water vapor permeability. The micro climate a PV-module sees at its surface was monitored during accelerated IEC tests and at outdoor test sites located in four different climatic regions. These measured values were used for FEM based simulations of the water ingress into PV-modules. The results show the speed and the amount of water uptake under IEC-test conditions as damp heat, humidity freeze and thermal cycling tests compared with the water ingress under the different climates. It can be stated that the IEC-damp-heat test provokes almost two times higher water concentrations in the encapsulant between cell and glass than outdoor weathering can adjust over 20 years. The humidity freeze test shows a similar behavior and even the thermal cycling test results in a slightly water uptake in the back sheet.

Most photovoltaic (PV)-modules have polymeric materials as encapsulants and back sheets. Usually these materials are not water vapour-tight and air-tight, but allow permeation of gases from the ambient atmosphere, especially oxygen and water vapour, which could contribute to degradation of the PV-modules.This work gives a short overview on how the permeation process through polymers takes place and how it is influenced by the material properties and ambient conditions. Results of permeation and diffusion measurements for water vapour as well as oxygen are shown for various encapsulation and back sheet materials with special focus on temperature dependence. The results demonstrate differences in permeability and temperature dependence for the investigated materials, but also show similarities for material groups. All investigated materials feature a Fickian behaviour within the measurement conditions even when crossing glass temperature or melting temperature. With these results, an Arrhenius-model was fitted to extrapolate permeation and diffusion values to a temperature range the PV-modules can be exposed to during lifetime.

The peel test is a very simple and fast method to determine the adhesion of interconnector ribbons to solar cell metallizations. It is part of the solar cell standard DIN EN 50461 and is, due to its ease of use, widely accepted to qualify cell metallizations and the soldering process. In the standard a force of 1 N per mm of joint width is specified but other relevant quantities are missing, for example the peeling angle. We show that this lack of specification enables the manipulation of peel testing results. We therefore apply the mechanical theory of Kinloch [1] where measured peel forces are translated into adhesive fracture energies GA. The fracture energy is a geometry-independent parameter that describes the energy to break the interfacial bondings at the peel front. It incorporates the dimensions of the ribbon and its stress-strain-curve. We perform 86 peel experiments at 90°, 135° and 180° of ribbons on continuous front side busbars of cells from one stringing batch. While the median forces for 90°(3.07 N), 135°(2.35 N) and 180°(3.39 N) differ by up to 30.4% we find the median adhesive fracture energies to deviate by only 17.4%. Using the same adhesive fracture energy (260 J/m2) for a 45° peel test we expect peel forces of 7.45 N which is factor 2.4 (2.2) higher than the 90° (180°) peel forces.

Solar resource assessments use solar radiation data from past observations to estimate the average annual solar radiation over the expected lifetime for a solar energy system. However, solar radiation at the Earth’s surface is not stable over time but undergoes significant long-term variations often referred to as “global dimming and brightening”. This study analyzes the effect of these long-term trends on solar resource assessments. Based on long-term measurement records in Germany, it is found that the additional uncertainty of solar resource assessments caused by long-term trends in solar radiation is about 3% on the horizontal plane and even higher for tilted or tracked planes. These additional uncertainties are not included in most uncertainty calculations for solar resource assessments up to now. Furthermore, for the measurement stations analyzed, the current irradiance level is about 5% above the long-term average of the years 1951–2010. Since the direction of future trends in solar radiation is not known, different possibilities to estimate the future solar resource are compared. In view of long-term trends that could extend beyond the period of past observations and beyond the projected lifetime of a solar energy application, a paradigm shift is proposed: instead of using the longest possible period to calculate an average value, only the 10 most recent years should be used as the estimator for future solar irradiance.

This paper focusses on the physical conditions for a degradation mechanism of photovoltaic modules, known as potential-induced degradation. The analysis was made on several levels. At first, the influence of humidity and temperature on the potential-induced leakage current has been investigated, the second step consists of an accelerated test scheme in a climatic chamber and the third one is outdoor exposure with high voltage stress in two different climate regions. The humidity has a huge impact on the leakage current. Therefore, a test in the climate chamber accelerates the stress found in the field of some orders of magnitude.

The degradation of the edge regions of crystalline silicon cells after damp-heat tests is a common phenomenon which can be observed in the electroluminescence images of most c-Si PV modules after damp-heat aging. However, the origin of this damp-heat induced degradation effect is unknown. Therefore, we investigated the degradation behavior of laminates with different designs, including laminate types with an open, thus breathable, front-side and two standard designs with one or two layers of EVA in front of the cell, respectively. This way, the influence of permeation properties and possible barrier effects on the degradation of the cell were investigated. The laminates were subjected to damp-heat aging tests at 80% r.h., 80 °C and 90 °C, respectively, for up to 2500 h. Electroluminescence imaging showed degradation after 2000 h of damp-heat aging at 90 °C for the standard laminate designs. No cell degradation was found for the breathable laminates. Measurements of the internal quantum efficiency (IQE) did not reveal a change of the recombination rate, thus the corrosion of the grid is the most likely cause of the degradation. This hypothesis was confirmed by an increased series resistance in the degraded areas. In those areas, aggregates of small needles were observed which could be identified as organic lead compounds by EDX. Since no hints of degradation could be found for the breathable laminates, an impact of the acetic acid as one corrosive degradation product from the encapsulant on the metal corrosion is very likely.

This paper presents recent progress in reducing the measurement uncertainty for crystalline silicon (c-Si) and thin-film PV modules. It describes the measurement procedure and the uncertainty analysis, as applied at the CalLab PV Modules, Fraunhofer ISE's laboratory for module measurements. The uncertainty analysis covers the complete calibration process in detail, including measurements, correction to standard testing conditions, and determination of electrical module parameters (ISC, PMPP, VOC, etc.) from the I-V curve. Differences between c-Si and thin-film modules are addressed, most importantly in terms of spectral mismatch factor and short timescale stability problems. The paper outlines the importance of a comprehensive quality assurance system in a calibration laboratory as a prerequisite for accurate measurements on a daily basis. Particular attention is paid to results from a series of measurements taken every three weeks over a three-year period and conducted as part of the quality assurance system. In conclusion, this paper introduces a best-case uncertainty for c-Si module calibration of 1.6% for PMPP and 1.3% for ISC. This represents the lowest reported uncertainty for full size module calibration in a laboratory so far. The presented uncertainty in PMPP of cadmium telluride and single-junction amorphous silicon modules is 2.9% and 1.8%, respectively. All mentioned uncertainties are expanded uncertainties (k = 2).

Electrically conductive adhesives (ECA) provide an alternative lead-free interconnection technology for crystalline silicon solar cells with lower thermomechanical stress than standard soldering. They show high potential for use in emerging cell concepts like metal-wrap-through (MWT) or heterojunction technology. Obviously, curing of ECA is a critical step along the interconnection process. Understanding and predicting its cure kinetics is essential for cost-effective and reliable module manufacturing. The cure reaction of an ECA can be described by an autocatalytic reaction model. In order to determine the model parameters, empirical kinetic information of the ECA is needed, which we obtain with dynamic differential scanning calorimetry (DSC). With the use of isoconversional methods the activation energy in dependence of the degree of cure is determined. The model calculates the degree of cure for any given temperature profile. We validate the model with an arbitrary t emperature profile in the DSC and find good agreement between experiment and simulation within 3-8% absolute difference in the degree of cure. As the methods given in this paper are easily adopted for the crosslinking reaction of ethylene-vinyl acetate (EVA), we simulate both the curing of ECA and the crosslinking of EVA during a typical lamination process.

Solar cell processing into modules is mostly responsible for the product's reliability, has a severe impact on product costs and controls 10–15% of its efficiency. This article gives an overview on current module technology and highlights innovative approaches to reduce material cost and increase module efficiency. High potential approaches like back contact technology are those that simultaneously address cell and module technology to offer efficiency gains in the range of 10%.Module reliability expectations of 25 years or more require quality assurance beyond the common type approval standards. In its second part, the article addresses stress factors for PV modules. To ensure fast innovation cycles, accelerated aging tests are used to reproduce these stress factors in the laboratory. Results from certification testing are discussed as well as new approaches for improved testing. More realistic test results can be obtained by simulating combinations of stress factors.

Die dynamische Marktentwicklung mit vorübergehendem Siliziummangel und Innovationsschub im Schlepptau sowie die steile Preissenkungskurve haben eine Vielfalt von Optionen für PV-Anlagen auf die Menükarte von Kleinanwendern wie Kraftswerksprojektierern gebracht. Während die Kellner durchreichen was gut riecht und die Köche in vielstimmigem Kanon ihre jeweiligen Kreationen besingen, sehnt sich der vermeintliche Genießer nach guten Empfehlungen von fachkundigen Gourmets.

Raman Probe Spectroscopy as a powerful tool for analyzing the degradation behavior of encapsulants in c-Si based PV modules is reported. A non-destructive and quick testing method is needed in order to follow material changes during the aging of PV modules. Two types of c-Si PV modules with ethylene vinyl acetate (EVA) encapsulation have been aged indoors under damp-heat conditions (85% r.h./85 °C) and under combined UV/moisture conditions, respectively. The aged modules as well as a non-aged reference module for each type were analyzed by Raman Spectroscopy. The degradation of the encapsulant was observed, resulting in an increasing fluorescence background, as well as changing intensities of EVA Raman peaks. A lateral non-uniformity of the fluorescence intensity of and the EVA CH stretching vibration intensity ratios, depending on the position above the cell as well as from the aging condition, could be observed and it might be an indicator for the diffusion of water i n the encapsulant.

As it makes its way towards a non-subsidised market, the photovoltaic sector has to deal with decreasing margins. To ensure investment goals are met in spite of this, it is imperative that PV power plants generate optimal yields. Comprehensive quality assurance for PV power plants covers all phases of the completion process from the planning to system operation. This article explains the extent of standard quality assurance measures that include yield assessments, module measurements, system testing and yield monitoring. It outlines the potential of linking these quality assurance measures and stresses the importance of the measures themselves being of high quality. Up-to-date scientific findings from Fraunhofer ISE are presented in order to further optimise quality assurance measures.

Measurement results from a worldwide intercomparison of photovoltaic module calibrations are presented. Four photovoltaic reference laboratories in the USA, Japan and Europe with different traceability chains, measurement equipment and procedures, and uncertainty estimation concepts, participated. Seven photovoltaic modules of different technologies were measured (standard and high-efficiency crystalline silicon, cadmium telluride, single and double-junction amorphous and micromorph silicon). The measurement results from all laboratories and for all devices agreed well. Maximum power for the crystalline silicon samples was within ±1.3% for all thin-film modules roughly within ±3%, which is an improvement compared to past intercomparisons. The agreement between the results was evaluated using a weighted mean as a reference value, which considers results-specific uncertainty, instead of the widely used unweighted arithmetic mean. A further statistical analysis of all deviations between results and the corresponding reference mean showed that the uncertainties estimated by the participating laboratories were realistic, with a slight tendency towards being too conservative. The observed deviations of results from the reference mean concerned mainly short-circuit current and fill factor. Module stability was monitored through repeated measurements at Fraunhofer ISE before and after measurements at each of the other participating laboratories. Based on these re-measurements, stability problems that occurred for some thin-film modules and influenced the results were analyzed and explained in detail.

Corrosion can seriously affect the service life of components for solar energy con- version. We present results of mapping the potential of atmospheric corrosion in coastal regions with the aid of a Geographical Information System (GIS). Concentration of sea salt aerosols, which are the main atmospheric pollutants in maritime coastal regions, gives an indication of the probability of the atmospheric corrosion leading to PV-module degradation. Two approaches to estimate the distribution of sea salt aerosol across the coastal regions worldwide are investigated. The first approach is a geo-statistical analysis that has been used for interpolating chloride deposition data. The second approach is based on modeling the environmental conditions, which are affecting source and distribution of airborne salinity. The comparison of these two approaches provides high accuracy in the description of the variation in airborne salinity across the coastal regions. The assessment of the atmospheric corrosion in coastal regions is based on the international standard ISO 9223. The corrosivity classification is simply defined by three parameters: SO2 pollution, airborne salinity, and relative humidity. A combination of the results from the geo-statistical approach and modeling is used; the result is a map of atmospheric corrosion in coastal regions. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI

Desert areas are noteworthy for solar system installation due to high yearly global irradiance. These arid regions bear extreme conditions for surfaces, like glazing and mirrors, of solar thermal systems. Surfaces are targets for soiling because of wind and high dust loads. Soiling is causing a decrease in transmittance that limits the overall performance. At a certain level depending on surface properties, like functionality and their reliability, is surface material soiling-prone. For surface qualification is a reproducible soiling test needed. An in-house developed artificial soiling device achieves this purpose. Realistic dust deposition is used to test the functionality and properties of surfaces for application in arid regions. The parameter study points out the connection between properties of surfaces and the adhesion behavior of real dust. Soiled surfaces are analyzed by by spectroscopic (FT-IR) and gravimetric measurements.