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For decades, photovoltaic (PV) module yellowing caused by UV exposure has been observed on solar arrays in operation. More than an aesthetic inconvenience, this phenomenon can severely impair module performance and promote other degradation mechanisms by undermining the photoprotection provided by encapsulation. To understand how this reaction may affect current encapsulation materials, silicon heterojunction (SHJ) monocell modules with either UV‐cut or UV‐transparent commercial encapsulants were aged under UV irradiation and examined by visual inspection, fluorescence imaging and flash tests. Despite the photoprotection they provide, only the encapsulants that were stabilised by UV absorbers underwent discolouration. On the one hand, UV absorber photodegradation is responsible for the formation of yellow chromophores that affect light transmission to the cell, which could cause net decrease in the photogenerated current high as 4% after 4200 h of accelerated UV ageing. On the other hand, UV‐induced degradation of SHJ solar cells only accounts for a lower photogenerated current loss (3%), in contrast with previous observations in the literature. According to the behaviour of the current encapsulation formulation, the stability of UV absorbing additives has to be improved to ensure the durability of the device over 30 years. [ABSTRACT FROM AUTHOR]

The field‐measured current–voltage (I–V) curves of photovoltaic (PV) modules need to be corrected to Standard Test Conditions (STC) in order to estimate the degradation rates. STC correction procedures have various attributes such as accuracy, requirement of minimum number and types of I–V curves, required irradiance range, and the type of correction (specific points or entire I–V curve) that determine their optimality for specific applications. This paper presents the investigation of accuracy and constraints of six different STC correction procedures for high‐throughput field I–V measurements through experimental and simulation studies. Following STC correction procedures are considered in this paper: IEC 60891‐Procedure 1, IEC 60891‐Procedure 2, Modified IEC 60891‐Procedure 1, Standard Irradiance and Desired Temperature (SIDT) procedure, Anderson procedure, and Voltage‐Dependent Temperature Coefficient (VDTC) Procedure. Eight different simulation models for predicting the performance of PV modules at arbitrary irradiance and temperature are compared, and the simulation model that yields lowest root mean square error and the most accurate estimation of power temperature coefficient is identified. The simulated I–V curves using this model and the experimentally measured I–V curves on a flash tester at different temperatures and irradiances are provided as an input to all of the STC correction procedures. The average percentage errors in correction of maximum power (Pmax), open‐circuit voltage (Voc), short‐circuit current (Isc), and fill factor (FF) were determined as a function of irradiance and temperature during measurement. Systematic biases introduced during correction by certain procedures were also identified. Based on the error estimation, constraints of various procedures, and requirements of high‐throughput field I–V measurements, the most optimal STC correction procedure was identified. Moreover, the analysis of the root cause of superior performance of this procedure is also presented. [ABSTRACT FROM AUTHOR]

The authors report on the light‐ and elevated temperature‐induced degradation (LeTID) effect observed on bifacial photovoltaic modules and its potential impact on photovoltaic plants performance. Indoor LeTID quantification using indoor carrier‐induced degradation (CID) is carried out using current injection. Power measurements yielded higher LeTID sensitivity for the rear side of bifacial modules compared to the front side, hence leading to a variation of the bifaciality factor by several percentage points. The difficulty in evaluating the maximal power degradation caused by LeTID is also highlighted as a reduced number of samples are used most of the time and as cells within a single module do not have always the same performance evolution trends. Using indoor CID results with the help of empirical fitting and Arrhenius relation, the yield impact of LeTID on a bifacial power plant is simulated under three different climates. Modeling results help to identify the main parameters related to LeTID modules sensitivity that impact photovoltaic (PV) plants yield: maximal power degradation, stabilized power value after regeneration, activation energy value, and LeTID kinetics. In some cases, the yield variation caused by LeTID sensitive modules could be mitigated by carefully selecting the modules as a function of climatic conditions. [ABSTRACT FROM AUTHOR]

Automatic defect detection in electroluminescence (EL) images of photovoltaic (PV) modules in production line remains as a challenge to replace time‐consuming and expensive human inspection and improve capacity. This paper presents a deep learning‐based automatic detection of multitype defects to fulfill inspection requirements of production line. At first, a database composed of 5983 labeled EL images of defective PV modules is built, and 19 types of identified defects are introduced. Next, a convolutional neural network is trained on top‐14 defects, and the best model is selected and tested, achieving 70.2% mAP50 (mean average precision with at least 50% localization accuracy). Then, through analyzing an object detection‐based confusion matrix, recognition bias and detection compensation in missed defects that restrain the best model's mAP50 are discovered to be harmless to normal/defective module classification in real production line. Finally, after setting specific screen criteria for different types of defects, normal/defective module classification is conducted on additionally collected 4791 EL images of PV modules on 3 days, and the best model achieves balanced scores of 95.1%, 96.0%, and 97.3%, respectively. As a result, this method surely has a highly promising potential to be adopted in real production line. [ABSTRACT FROM AUTHOR]

Commercially different variants of ethylene‐vinyl acetate (EVA) encapsulants are available in the photovoltaic (PV) market. Photobleaching and discoloration are the two most commonly observed phenomena, and their initiation may be different for different encapsulants. To investigate the EVA encapsulant photobleaching and discoloration, solar cell laminates having different EVA films (UV‐transparent [T], UV‐cut [C], and combination of the two [TC]) were tested in Xenon test chamber. High temperatures are created in the laminates during the aging tests by using a thick insulation layer behind the backsheet. The UV fluorescence images and grayscale profile show clear signs of photobleaching and discoloration. It is found that the oxygen diffusion coefficient of the T sample is four and nine times slower than the TC and C samples, respectively, in the photobleached region. Fluorescence imaging and spectra and Raman spectra were taken before and after the accelerated test and indicate that discoloration causing fluorophores generation is higher after the photobleached region for transparent and combined EVAs, whereas higher at the center for UV‐cut EVA laminates. A colorimeter was used to measure the Yellowness Index of the samples before and after the accelerated aging test. This work will help in the early detection of photobleaching and discoloration of any encapsulant used in the PV modules. This method will also help to study the behavior of encapsulants in different climatic conditions like hot, cold, dry, humid, and their combinations by simulating the same in an accelerated weathering chamber by using the different insulation thickness. [ABSTRACT FROM AUTHOR]

Adhesion measurements and chemical characterization of the encapsulant/silver metallization interface of a photovoltaic (PV) module through temperature, humidity, and voltage bias exposures were conducted. Results demonstrate two independent degradation mechanisms: (a) with voltage bias, the ionic conduction of Na+ ions through the encapsulant results in the formation of sodium silicate at the silver metallization surface, thereby weakening that interface and (b) with moisture ingress, dissociation of the silane bonding to silver in the silver oxide similarly weakens this interface resulting in significantly lower debond energies. [ABSTRACT FROM AUTHOR]

Accelerated tests were used to study potential-induced degradation (PID) in photovoltaic (PV) modules fabricated from silicon heterojunction (SHJ) solar cells containing tungsten-doped indium oxide (IWO) transparent conductive films on both sides of the cells and a rear-side emitter. A negative bias of -1000 V was applied to a module with respect to the cover glass surface in a chamber maintained at 85°C, which significantly reduced the cell's short-circuit current density (Jsc) within several days. Based on dark current density-voltage and external quantum efficiency measurements, the reduction in the Jsc was attributed to optical losses rather than carrier recombination. X-ray absorption fine structure spectroscopy showed the formation of metallic indium (In) in the IWO layers of a degraded cell, which suggests that the root cause of the optical loss was a darkening of the front IWO layers caused by the precipitation of metallic In. In extremely severe PID tests, the SHJ PV modules exhibited not only a further reduction in the Jsc but also a moderate reduction in the open-circuit voltage (Voc). These Jsc and Voc reductions were probably caused by sodium being introduced into the base region of the cells. A comparison of the PID test results of the SHJ PV modules with those of other types of PV modules indicates that SHJ PV modules have a relatively high resistance to PID. As a module with an ionomer encapsulant exhibited little degradation, their high resistances to PID may be further improved by using encapsulants with high electrical resistances. [ABSTRACT FROM AUTHOR]

Herein, we present a prototype of a photovoltaic module that combines a luminescent solar concentrator integrating one-dimensional photonic crystals and in-plane CuInGaSe2 (CIGS) solar cells. Highly uniform and wide-area nanostructured multilayers with photonic crystal properties were deposited by a cost-efficient and scalable liquid processing amenable to large-scale fabrication. Their role is to both maximize light absorption in the targeted spectral range, determined by the fluorophore employed, and minimize losses caused by emission at angles within the escape cone of the planar concentrator. From a structural perspective, the porous nature of the layers facilitates the integration with the thermoplastic polymers typically used to encapsulate and seal these modules. Judicious design of the module geometry, as well as of the optical properties of the dielectric mirrors employed, allows optimizing light guiding and hence photovoltaic performance while preserving a great deal of transparency. Optimized in-plane designs like the one herein proposed are of relevance for building integrated photovoltaics, as ease of fabrication, long-term stability and improved performance are simultaneously achieved. [ABSTRACT FROM AUTHOR]

We are presenting the module integration of busbar-free back-junction back-contact (BJBC) solar cells. Our proof-of-concept module has a fill factor of 80.5% and a conversion efficiency on the designated area of 22.1% prior to lamination. A pulsed laser welds the Al metallization of the solar cells to an Al foil carried by a transparent substrate. The weld spots electrically contact each individual finger to the Al foil, which serves as interconnect between different cells. We produce a proof-of-concept module using busbar-free cell strips of 25 × 125 mm2. These are obtained by laser-dicing of a 125 × 125 mm2 BJBC solar cell. The fill factor of this module is increased by 3.5% absolute compared with the initial cell before laser-dicing. This is achieved mainly by omitting the busbars and reduction of the finger length. The improvement of the module fill factor results in an increase in the module performance of 0.9% absolute before lamination in comparison with the efficiency of the initial 125 × 125 mm2 BJBC solar cell. Hence, this interconnection scheme enables the transfer of high cell efficiencies to the module. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A high-quality encapsulation process is crucial to ensuring the performance and long-term reliability of photovoltaic (PV) modules. In crystalline Si technology-based modules, poly (ethylene-co-vinyl acetate) (EVA) is the most widely used PV encapsulant. Its encapsulation process is usually performed in a flat-bed vacuum bag laminator. In certain types of laminators, cooling press can be applied to the module cooling process after the module encapsulation, leading to a much higher cooling rate (~100 °C/min) than conventional natural cooling due to the application of water cooling circulation and mechanical pressure on the modules. In this work, the effect of the cooling press on the encapsulation properties of PV modules with EVA as the encapsulant are assessed on the aspects of residual stress in the modules, peeling strength between glass and EVA, and the resulting EVA gel content after encapsulation. The results show that the cooling press influences the encapsulation properties of PV modules. In particular by applying the cooling press after encapsulation, the residual normal stress in the Si solar cell in the encapsulated module after cooling can be reduced by as much as 22 ± 2 to 27 ± 3% depending on the EVA gel content, whereas the peeling strength between front glass and EVA is increased by ~ 10%. This work should help the further optimization of PV module encapsulation processes aimed at improving module encapsulation quality. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the integrated development of back-contacted solar cells and an adequate module interconnection for a high-efficiency photovoltaic module. We report on a large area (125 × 125) mm2 back-junction back-contact n-type solar cell metallized with aluminum having a total area conversion efficiency of 20.7%. To transfer the high conversion efficiency to the module, we use the laser welding process named aluminum-based mechanical and electrical laser interconnection for module integration of these back-contacted solar cells. We further analyze the impact of the busbars of our back-junction back-contact cells on the cell performance and report on optimization of the cell/module interface. The new cells have an adapted rear-side geometry by omitting the emitter busbar. A proof-of-concept module consisting of these cells is presented. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT The variables presented in the current-voltage equation of a photovoltaic (PV) device are usually called PV parameters. There are several different methods for PV parameter extraction from measured data according to different models. However, many of these methods provide results that do not represent I-V curves of thin films devices correctly. This can occur because either the applied model or the PV parameter extraction methods are not suitable. It is also possible that the extracted parameters provide a good mathematical representation of the curves but without physical meaning (e.g. negative series resistance). This work presents a method for PV parameter extraction based on a modified double-diode model. In this model, the ideality factor related to the recombination of the charge carriers in the space-charge region is assumed as a variable. This method has been tested for different I-V curves of different PV module technologies providing very good results and parameters with physical meaning in all the cases. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The energy requirements for the production of PV modules and BOS components are analyzed in order to evaluate the energy pay-back time and the CO2 emissions of grid-connected PV systems. Both c-Si and thin film module technologies are investigated. Assuming an irradiation of 1700 kWh/m2/yr the energy pay-back time was found to be 275-3 years for present-day roof-top installations and 3-4 years for multi-megawatt, ground-mounted systems. The specific CO2 emission of the rooftop systems was calculated as 50-60 g/kWh now and possibly 20-30 g/kWh in the future. This leads to the conclusion that in the longer term grid-connected PV systems can contribute significantly to the mitigation of CO2 emissions. [ABSTRACT FROM AUTHOR]