This PDF file contains the front matter associated with SPIE Proceedings Volume 8825, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Understanding transparent conductive oxide (TCO) degradation is critical to improving stability and lifetime of both organic and inorganic thin lm PV modules, which utilize TCOs, like indium tin oxide (ITO), aluminumdoped zinc oxide (AZO) and uorine-doped tin oxide (FTO) as electrodes. These TCOs must retain their long-term functionality in diverse outdoor environments. In addition to bulk material degradation, interfacial degradation, a frequent avenue for failure in PV systems, is promoted by exposure to environmental stressors such as irradiance, heat and humidity. ITO, AZO and FTO samples in an open-faced con guration were exposed to damp heat and ASTM G154 for up to 1000 hours. The e ect of exposure on electrical and optical properties and surface energies of cleaned samples was measured. Yellowness, haze, water contact angle and resistivity of the di erent materials trended di erently with exposure time and type, indicating the activation of distinct degradation mechanisms. An encapsulated con guration study was conducted on ITO and AZO, exposing samples to the above accelerated exposures and two outdoor exposures (1x suns and 5x suns on a dual axis trackers), with and without PEDOT:PSS layers. PEDOT:PSS increases the yellowness and haze of ITO and AZO, but does not accelerate the increase in resistivity, suggesting that the optical and electrical degradation mechanisms are not coupled. Additionally, the hazing/roughening mechanism of PEDOT:PSS on AZO appears to be photo-sensitive; 5x outdoor exposure samples demonstrated distinctly higher haze than damp heat exposed samples.

The International PV Module Quality Assurance Task Force was created in 2011 to develop a rating system that provides comparative information about the relative durability of PV modules. The identification of accelerated stress tests that can provide such comparative information is seen as a major step toward being able to predict PV module service life. This paper will describe the methodology being employed by the Task Force as well as the efforts of the Ten Task Groups formed by the Task Force. Since this is an ongoing effort, this paper will serve as a progress report.

Infrared (IR) lock-in thermography (LIT) has been successfully used for defect detection in solar cells. Depending on the experimental setup, defects such as shunts, series resistances, pre-breakdown regions, etc., can be qualitatively visualized or quantitatively measured. IR-LIT results improve the spatial resolution (SR) in defect visualization and the signal-tonoise ratio (SNR) between defects and sound regions compared to classic DC thermography. The same results have been accomplished on solar modules, considered as an ensemble of solar cells electrically connected. The main problem that arises in IR-LIT technique is encapsulated modules/cells measurement, because most glasses used for encapsulation are opaque in the IR region. In this research, IR opacity of encapsulating glass is treated from a thermal point of view. Solar cells have been considered as a heat source with a heating frequency actively generated by a modulated forward polarization. The encapsulation behaves as a thermal low pass filter, whose cutoff frequency has been calculated. In the experiments, a modulated forward electrical polarization has been applied to a solar module in the dark. The tested sample has been a standard solar module of 36 cells connected in series. Thermal images have been acquired from the side of the external glass surface by an IR camera. A large improvement of SR and SNR has been demonstrated for shunt detection when the modulation frequency is below the cutoff.

Within this contribution several 3D nite- element- models have been created in order to simulate processing of solar cells (lamination, soldering) as well as mechanical bending. The stress state for each load case was analysed with respect to magnitude and direction of principal stresses. For the process steps there are di erent mechanisms that induce stresses in the silicon. For soldering the mismatch in CTE is dominant. For lamination, bending around the ribbon is the dominant mechanism, which is due to the contraction of the encapsulant. Furthermore, it was found that cooling during lamination applies the highest loads into a solar cell. Mechanical bending was simulated and investigated experimentally by 4-point-bending with di erent load ramps. Due to strain-rate dependent properties of the encapsulant EVA there is a minor in uence on the load de ection behaviour but a large in uence on the reliability of a solar cell. By means of a parameter study the in uence of the cell distance on mechanical reliability was investigates. It was shown that a small cell distance (here < 3mm) increases the probability of failure of the solar cell signi cantly.

The qualification tests described in IEC 61215 for the c-Si PV modules are essentially pass/fail tests that assist in avoiding infant mortality. This paper reports on the baseline test procedure carried out on PV modules at Florida Solar Energy Center that go beyond the pass/fail criteria of the qualification tests and obtain information about the degradation modes and mechanisms. The importance and limitations of the various characterization techniques are described. Electroluminescence imaging has been used to detect and categorize the faults at the cell level. Indoor infrared imaging has been used to study the quality of electrical interconnects in the module. The infrared imaging carried out on the modules while they are undergoing outdoor exposure has provided information about the presence and distribution of hot spots in these modules. Conventionally, the insulation resistance tester has been used mostly for the dry and wet leakage test. In this study, the importance of the polarization index test and voltage excursion test are described. The use of these tests is essential to provide insight into the modes and mechanisms of degradation, during reliability and durability studies of PV modules. A predictive model for the service life of a PV module may be developed through the results obtained from these characterization techniques in conjunction with long-term exposure and accelerated lifetime tests.

Monocrystalline silicon wafer is up-to-date most used material for the fabrication of solar cells. The recent investigation shows that the quality of cells is often degraded by structural defects emerging during processing steps. Hence the paper gives first an overview of solar cell efficiency investigation on macroscale. Then a detection and microscale localization of tiny local defects in solar cell structures which evidently affect electrical and photoelectrical properties of the cells is targeted. The local defects can be classified as microfractures, precipitates and other material structure inhomogeneities. Detection and localization of the defects in the structure and the assigning of particular defects to corresponding degradation of photoelectrical parameters are key points for solar cell lifetime and efficiency improvement. Although the breakdown can be evident in current-voltage plot, the localization of defects on the sample has to be provided by microscopic investigations as well as by defects light emission measurement under electrical bias conditions. The experimental results obtained from samples where the defects were microscopically repaired by focused ion beam are presented. Electrical and photoelectrical properties of sample before and after milling processing are also discussed.

A widely cited approximation in the solar industry is that “one week of xenon arc weather-o-meter exposure is equivalent to one year of field exposure.” This statement is a generalization of test data generated in the mid-1990s as part of the NREL managed PVMaT-3 project. This approximation was based entirely upon yellowing of first generation EVA-based encapsulants in two different accelerated test conditions, xenon arc and mirror accelerated outdoor aging. First generation EVA encapsulants were developed by STR under the JPL solar project (1975-1986) and exhibit yellowing (or browning) with exposure to UV and heat. This yellowing mechanism was understood and resolved with newer generation EVA encapsulation products introduced in late 1990s. Modules were manufactured at the end of the PVMaT-3 project that included both older and newer generation encapsulants. Those modules were on a two-axis tracker in Arizona from 1996 to 2012 and are now undergoing diagnostic tests. Older generation standard-cure encapsulant used in these modules exhibited severe browning over cells and the modules exhibit approximate power loss of about two percent per year. This same standard cure encapsulant material has been tested with updated xenon arc exposure methods and optical transmission tests to estimate the loss in power due only to browning and reduction in light transmission.

The optical transmittance of encapsulation materials is a key characteristic for their use in photovoltaic (PV) modules. Changes in transmittance with time in the field affect module performance, which may impact product warranties. Transmittance is important in product development, module manufacturing, and field power production (both immediate and long-term). Therefore, an international standard (IEC 62788-1-4) has recently been proposed by the Encapsulation Task-Group within the Working Group 2 (WG2) of the International Electrotechnical Commission (IEC) Technical Committee 82 (TC82) for the quantification of the optical performance of PV encapsulation materials. Existing standards, such as ASTM E903, are general and more appropriately applied to concentrated solar power than to PV. Starting from the optical transmittance measurement, the solar-weighted transmittance of photon irradiance, yellowness index (which may be used in aging studies to assess durability), and ultraviolet (UV) cut-off wavelength may all be determined using the proposed standard. The details of the proposed test are described. The results of a round-robin experiment (for five materials) conducted at seven laboratories to validate the test procedure using representative materials are also presented. For example, the Encapsulation Group actively explored the measurement requirements (wavelength range and resolution), the requirements for the spectrophotometer (including the integrating sphere and instrument accessories, such as a depolarizer), specimen requirements (choice of glass-superstrate and -substrate), and data analysis (relative to the light that may be used in the PV application). The round-robin experiment identified both intra- and inter-laboratory instrument precision and bias for five encapsulation materials (encompassing a range of transmittance and haze-formation characteristics).

Polymeric backsheets form the outer protective layer of most crystalline and multi-crystalline silicon cell photovoltaic panels. The mechanical, electrical, optical and chemical properties and durability of these backsheets are critical to the long term reliability, durability and safety of the photovoltaic modules. The stability of these backsheet properties is typically determined based on accelerated testing using individual stresses. However, the impact of multiple stresses applied sequentially or simultaneously can lead to changes in materials properties that are more predictive of performance in the field. An important consideration in the development of accelerated test protocols is the level and duration of the stress, including temperature variation, light intensity and spectral power distribution, humidity, rainfall and powered module current. In this paper, we discuss observations of the aging and degradation of solar panel from the field. Then how these changes correlate to accelerated testing results, and how accelerated tests can be modified to better match observations in the field.

This addresses two separate issues that the human mind often confuses. The first is that not all PV module degradation data is fully and accurately interpreted. Second is the assumption that full and accurate data interpretation will necessarily lead to deeper insight and more accurate future predictions. It is, however, not clear how much additional information can be gained from secondary signals (like luminescence) when they are “optimized.” Often, these issues are reflected in data analyses that deal only with linear approximations., ignoring data that do not fit linear patterns. When claims are made that such data isn’t public or does not exist with great enough accuracy, this may or may not reflect the real situation for making more accurate predictions. While it may be instructive to understand PV losses in terms of per year (annual) loss, it has to be realized that failure and degradation may be different if multiple degradation mechanisms are effective. A confusion may exists between average and individual numbers and greater accuracy and more data will not automatically guaranty deeper insight into an issue or allow more accurate future projections for an individual case. The issue is whether or not more insight is gained by separation to identify the largest mechanism, or whether the correct combination of features minimizes degradation mechanisms. The results of the author’s personal home PV system (in its 7^th year) are presented.

In order to optimize and extend the life of photovoltaics (PV) modules, scienti c and mechanistic statistical analytics must be performed on a large sample of materials, components and systems. Statistically signi - cant relationships were investigated between di erent mechanistically based variables to develop a statistical pathway diagram for the degradation of acrylic that is important in concentrating photovoltaics. The statisti- cally signi cant relationships were investigated using lifetime and degradation science using a domain knowledge semi-supervised generalized structural equation modeling (semi-gSEM. Predictive analytics and prognostics are informed from the statistical pathway diagram in order to predictively understand the lifetime of PV modules in di erent stress conditions and help with these critical lifetime technologies.

A durable encapsulation scheme is of paramount importance to achieve long lifetime of the solar modules. Among other, water vapor and acetic acid are considered as important degradation factors. Various methods contributing to understand failure modes related to water vapor and acetic acid ingress are presented here. • Using 2D finite-element analysis in correlation with climatic data, a model is built to simulate water ingress within the module. A comparison between various climatic regions is given. • Real interfacial adhesion of encapsulant to glass is characterized before and after exposure to water vapor using a new compressive shear test.

The maximum system voltage for Photovoltaic systems is 1000 V in US. Some modules are designed to operate even at 1500 V, which is the limit for IEC low voltage systems. The high voltage bias between the cell circuit and frame of the module leads to a leakage current flowing through the insulation of the module to the ground. Over time, this leakage current causes migration of various species to and from the cell circuit, can result in slow degradation of the performance of PV module. It is important to understand the electric field distribution and leakage current pathways in the PV modules in order to study the system voltage induced degradation of PV modules. The leakage current from the PV modules deployed outdoor and under high voltage bias strongly varies with the environmental conditions. The lumped resistance models described in literature that attempt to explain the leakage current flow through the PV module do not provide adequate information about the distribution of leakage current through different layers of insulation present in the PV modules. In this paper, a Finite Element Analysis (FEA) based model for the insulation of PV module is described. It yields useful information about the distribution of electric field, potential and leakage current flowing through different layers of module. The model is also used to predict and analyze the changes in leakage current with changes in module packaging materials and grounding configurations.

The operating conditions of bypass diodes in PV modules deployed in the field are considerably harsher than the conditions at which the diode manufacturers test the diodes. This has a potential to significantly reduce the operating life of bypass diodes and has raised concerns about the safety and reliability of PV modules as a whole. The study of modes and mechanisms of the failures encountered in bypass diodes used in PV modules can provide important information which would be useful to predict the module lifetime. This paper presents the review of the failure modes and mechanisms observed in bypass diodes and current work related to reliability testing of bypass diodes. The International PV Module Quality Assurance Task Force has recommended following four potential areas of research to understand the reliability issues of bypass diodes: Electrostatic Discharge, reverse bias thermal runaway testing, forward bias overheating and transition testing of forward bias to reverse bias. As a joint collaborative effort between Florida Solar Energy Center and Solar and Environmental Test Laboratory at Jabil Inc., laboratory testing of bypass diodes on the guidelines provided by the International PV Module Quality Assurance Task Force has been initiated. Preliminary results from this work are presented in this paper.

CIGS is the most promising technology for thin-film solar cells with record efficiencies of 20.4 % on laboratory scale and 17.8 % aperture area efficiency on a 900 cm² module. Another important factor besides the cell efficiency is the reliability and long term stability of the manufactured modules, which can be assessed by accelerated ageing. In this contribution the accelerated ageing of CIGS mini modules has been investigated. Therefore, modules were dark annealed under dry heat conditions at different temperatures. During the endurance test a positive or negative bias was applied to the cells. In regular intervals the IV- and CV-characteristics were measured at room temperature. After an overall stress time of 3500 h the IV-characteristics were determined under different illumination conditions (intensity, spectral illumination). Our previous publications suggest a barrier at the back contact to explain the observed parameter drifts. This contribution is focused on the influence of different bias conditions during the endurance test on the generation of a back diode and on the change of the acceptor concentration. These parameter drifts have an impact on the open circuit voltage, fill factor and on the appearance of a cross over between dark and illuminated IV-characteristics. The interpretation of the observed parameter drifts was supported by SCAPS simulations based on the above mentioned back barrier model. As an outcome of the simulations signatures for the existence of a back barrier diode were established. IVmeasurements, temperature dependent V_oc measurements and SunsV_oc measurements are helpful means to detect such back diodes.

Qualification testing (QT) is the major means for making a viable photovoltaic (PV) device into a reliable and marketable product. It is well known, however, that the today’s PV modules (PVM) that passed the existing QT often exhibit premature field failures. Could the existing QT specifications and testing procedures be improved to an extent that if a PV device, module or a system passed the QT, there is a quantifiable and consistent way to assure that its performance in the field will be satisfactory and that its projected lifetime will indeed take place with the given confidence? The application of the probabilistic design for reliability (PDfR) concept enables one to provide an affirmative answer to this question. The attributes and challenges of this concept and the roles of its major constituents - failure oriented accelerated testing (FOAT) and physically meaningful predictive modeling (PM) - are addressed and discussed in detail.

Linking accelerated laboratory test to field performance for predicting the service life of polymeric materials are being investigated at NIST using the reliability-based methodology. Based on this methodology, a successful linkage between the laboratory and field exposure data for a model polymeric material has been made. Recently, this methodology, for the first time, was introduced to the lifetime assessment of PV polymeric materials. In this paper, a mechanistic study of the degradation of three unstabilized model ethylene vinyl acetate (EVA) systems---uncured EVA, cured EVA and laminated EVA---was carried out under accelerated laboratory exposure and outdoor exposure. The NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) was used for the accelerated laboratory tests, and the outdoor exposure was conducted in Gaithersburg, Maryland. Simultaneous multiple stresses, including temperature, relative humidity and UV radiation, were applied individually or in combination during SPHERE exposure. The effects of the environmental factors on the main degradation mechanisms of different EVA systems were investigated. The results showed that the UV radiation was the most important factor for the degradation of EVA and a synergistic effect occurred between UV radiation and relative humidity. A slower degradation rate was observed for the laminated system as a result of limited diffusion of O₂ and H₂O into EVA. It was also found that the substantial chemical changes of the uncured EVA system did not yield yellowing, which was dramatically different from the peroxide cured EVA system. Additionally, the chemical degradation modes of the three EVA systems exposed outdoors appeared to be similar to those exposed to the SPHERE. The implication of this work to the current test standards was discussed.

Continuing to better understand the performance of PV systems and changes in performance with the system life is vital to the sustainable growth of solar. A systematic understanding of degradation mechanisms that are induced as a result of variables such as the service environment, installation, module/material design, weather, operation and maintenance, and manufacturing is required for reliable operation throughout a system’s lifetime. We wish to report the results from an analysis of a commercial c-Si PV array owned and operated by DuPont. We assessed the electrical performance of the modules by comparing the original manufacturers’ performance data with the measurements obtained using a solar simulator to determine the degradation rate. This evaluation provides valuable PV system field experience and document key issues regarding safety and performance. A review of the nondestructive and destructive analytical methods and characterization strategies we have found useful for system, module, and subsequent material component evaluations are presented. We provide an overview of our inspection protocol and subsequent control process to mitigate risk. The objective is to explore and develop best practice protocols regarding PV asset optimization and provide a rationale to reduce risk based on the analysis of our own commercial installations.

Luminescent solar concentrators have been studied and improved for over 30 years. Of all moderate gain solar concentrator systems they are fundamentally the most attractive from a range of geometric and optical perspectives for many solar cell materials, for daylighting via light guides, and for some bio-applications. Of most significance is their étendue advantages over mirror and lens systems in terms of best dealing with the diffuse component and varying beam directions of solar radiation. Despite this and some attempted commercial ventures they have yet to achieve their potential. This paper addresses what is for the dominant class of such concentrators, those involving fluorophore doped polymers, especially PMMA, a core residual problem. Their long-term stability outdoors is insufficient. This is not due to UV effects and dye quenching, which can be controlled, but to fast local photo-thermal interactions between the activated dye molecules and the host material. Production of char like nanoscale absorbers may result. These absorb over a broad-band and though very dilute lower output transport efficiency in practical sizes. Data which led to this conclusion is presented, plus possible solutions. Other improvements in LSC polymer technology only have practical value if this core problem is first mitigated.

Microbial fuel cells (MFCs) are devices that use bacteria as the catalysts to oxidize organic and inorganic matter and generate current. Up to now, several classes of extracellular electron transfer mechanisms have been elucidated for various microorganisms. Shewanellaceae and Geobacteraceae families include the most of model exoelectrogenic microorganisms. Desulfuromonas acetoxidans bacterium inhabits aquatic sedimental sulfur-containing environments and is philogenetically close to representatives of Geobacteraceae family. Two chamber microbial fuel cell (0.3 l volume) was constructed with application of D. acetoxidans IMV B-7384 as anode biocatalyst. Acetic, lactic and fumaric acids were separately applied as organic electron donors for bacterial growth in constructed MFC. Bacterial cultivation in MFC was held during twenty days. Lactate oxidation caused electric power production with the highest value up to 0.071 mW on 64 hour of D. acetoxidans IMV B-7384 growth. Addition of acetic and fumaric acids into bacterial growth medium caused maximal power production up to 0.075 and 0.074 mW respectively on the 40 hour of their growth. Increasing of incubation time up to twentieth day caused decrease of generated electric power till 0.018 mW, 0.042 mW and 0.047 mW under usage of lactic, acetic and fumaric acids respectively by investigated bacteria. Power generation by D. acetoxidans IMV B-7384 was more stabile and durable under application of acetic and fumaric acids as electron donors in constructed MFC, than under addition of lactic acid in the same concentration into the growth medium.

The more and more solar power requirements and balance of system (BOS) cost saving issues, photovoltaic power plants have increasing system voltage, in Europe, for example, the system voltage requirements up to 1000 volts to 1500 volts. Solar module reliability expose to the high voltage stress (HVS) need reassessment. It is well-known that HVS can lower the PV power significantly that means potential induced degradation (PID) effect. However, the effects of the PID and other environmental conditions on module performance have not been included in the IEC qualification standards yet. In this paper we review various PV module type, example MG-Si, poly-Si, CIGS module and encapsulant sheets performance suffer high voltage stress effect. To evaluate module durability in the presence of continuous high voltage we used four accelerated tests to qualify the HVS effect. The first one is under room temperature, 100% relative humidity (RH), second method is room temperature and aluminum foil covered the front sheet, the third method is climatic chamber test at 85℃and 85% RH and the last one is the 60°C and 85%RH with -1000V bias applied to active layer, respectively. The I-V characteristics and Electroluminescence (EL) images have been measured after several time steps to quantify the degradation process of each module. Besides the recovery characterization was also investigation.

At present there are known many of diagnostic methods of detection large crystal lattice defects of silicon solar cells. This paper deals about results of new potential in to use one of characteristics luminescence radiation for detection defects of solar cells. So polarization spectroscopy of defect in solar cells may be used to fitting characterization of silicon solar cells. And this can lead to understand the electrical properties of defects in silicon solar cells and study of really formation defects. We used extending existing electroluminescence technology about polarization spectroscopy to yield the polarization of luminescence radiation by defect in solar cells. Radiation emitted by the solar cell has a wave character that can interact with the silicon structures or hypothetically thin reflectance layer of solar cells. In our research we can observed the linear partially polarization luminescence light on poly-silicon crack defect. Spectral response of using CCD camera is approximately 300 to 1100 nm. Sinusoid dependence of luminescence intensity on the angle of linear polarization analyzer rotation shown this fact. The degree of polarization depends on the material, in this case the character of defect. Polarized light can be obtained in various ways. This fact opens up for potential next new questions in this widely course of study diagnostics defects silicon solar cells.