Degradations of silicon photovoltaic modules: A literature review

Early degradation of silicon PV modules and guaranty conditions

Indoor and outdoor aging tests are common methods for PV module degradation investigation. But to what extend are accelerated indoor aging tests comparable to outdoor exposure tests? The impact of indoor and outdoor tests on the polymer degradation in full-size PV modules was investigated. Polymer aging within a PV module is one of the major factors influencing module performance in the course of its lifetime. Degradation phenomena like yellowing, delamination or changes in the elastic modulus of the encapsulation may lead to transmission losses, corrosion effects or cell cracks. Raman Spectroscopy has recently been reported by our group as a non-destructive, analytical method for encapsulation degradation analysis. The degradation of the encapsulation of indoor and outdoor aged crystalline silicon PV modules was examined by the means of Raman Spectroscopy with special attention to the spatial-dependency of the degradation. The investigated modules were subjected to several different accelerated aging procedures with a systematic variation of the climatic conditions temperature, humidity and UV. Identical modules were aged in different climates (arid, tropical, urban and alpine) for up to three years. The degradation of the encapsulant was observed, resulting in an increasing fluorescence background in the Raman spectra. A dependency of the aging process on the relative position to the edges of the cell was found. The aging conditions appeared to influence the spatial distribution of the fluorescence and therefore, the polymer degradation, markedly. Furthermore, correlations between accelerated aging tests and outdoor exposure tests could be found.

Major sources of performance degradation and failure in glass-encapsulated PV modules include moisture-induced gridline corrosion, potential-induced degradation (PID) of the cell, and stress-induced busbar delamination. Recent studies have shown that PV modules operating in damp heat at -600 V are vulnerable to large amounts of degradation, potentially up to 90% of the original power output within 200 hours. To improve module reliability and restore power production in the presence of PID and other failure mechanisms, a fundamental rethinking of accelerated testing is needed. This in turn will require an improved understanding of technology choices made early in development that impact failures later. In this work, we present an integrated approach of modeling, characterization, and validation to address these problems. A hierarchical modeling framework will allows us to clarify the mechanisms of corrosion, PID, and delamination. We will employ a physics-based compact model of the cell, topology of the electrode interconnection, geometry of the packaging stack, and environmental operating conditions to predict the current, voltage, temperature, and stress distributions in PV modules correlated with the acceleration of specific degradation modes. A self-consistent solution will capture the essential complexity of the technology-specific acceleration of PID and other degradation mechanisms as a function of illumination, ambient temperature, and relative humidity. Initial results from our model include specific lifetime predictions suitable for direct comparison with indoor and outdoor experiments, which are qualitatively validated by prior work. This approach could play a significant role in developing novel accelerated lifetime tests.

A preliminary study on potential of Very Large Scale Photovoltaic Power Generation Systems (VLS-PV) in deserts from economical and environmental view points has been studied. However, the data in the studies depend on site, country, price and so on. Therefore, a sensitivity analysis of the studies should be obtained. In this paper, five case studies of sensitivity analysis of VLS-PV systems were evaluated from economical and environmental view points. Case studies were set five cases; (1) PV module efficiency, (2) PV module degradation, (3) interest ratio and depreciation period, (4) labor cost and (5) cable. In summary, generation cost was affected by degradation, interest ratio, depreciation period and labor cost. Required energy and CO2 emission were affected by PV module efficiency and degradation ratio.

Experimental validation of performance and degradation study of canal-top photovoltaic system

Photovoltaic Platform for Investigating PV Module Degradation

<abstract> <p>Degradation of PV modules have a severe impact on its power-producing capabilities thus affecting the reliability, performance over the long run. To understand the PV degradation happening under the influence of local environmental conditions a survey was conducted on six polycrystalline silicon-based PV modules over five years. It has been observed that the average degradation rates stood at 1.02%/year at irradiances 800 W/m<sup>2</sup> and 0.99%/year at irradiances 600 W/m<sup>2</sup>, which are almost double the manufacturer proposed values. Upon further investigations, it has been found that discoloration of encapsulant in modules 3, 5, and 6 have been the main factor causing the reduction of the short circuit current (I<sub>sc</sub>) thus affecting the overall power production capacity of the installed PV system. Considering the amount of time, resources and manpower invested to perform this survey an alternate way of estimating the PV degradation rates is also investigated. The exponential decay factor-based model is adopted to correlate the encapsulant discoloration seen on-site in the form of a mathematical equation to predict the current loss. This loss is defined as the visual loss factor in this paper. Further, the output I-V curves are simulated using MATLAB Simulink-based mathematical model which also integrates visual loss factor (VLF) losses into it. Such simulated I-V curves have shown a good match with the measured I-V curves at the same irradiance with an error less than 3%. Authors anticipate that this modelling approach can open the door for further research in developing algorithms that can simulate the PV degradation rates.</p> </abstract>

Connecting material degradation and power loss of PV modules using advanced statistical methodology

Degradation analysis of polycrystalline silicon modules from different manufacturers under the same climatic conditions

Crystalline silicon PV modules has been in use for long time in many PV applications. It was not expected that PV modules of old technology will last for twenty years. A PV system which was installed in 1979 in the Libyan Desert is still running with a little decrease in the output power and small changes in its designed parameters. The crystalline silicon PV modules have proved of given an acceptable range of its nominal power rating for thirty one years of work. According to that, the life time of the crystalline silicon PV modules can be extended for more than forty years, and this will convince module manufacturers to give a PV module warranty for more than 30 years. PV Modules of front glass cover which has been in work for more than thirty years were tested and its IV curves were measured. A measurement setup for outdoor and indoor measurements of PV modules characteristics is used to evaluate the PV modules parameters. This paper presents the measuring results of outdoor and indoor measurements on the PV models which were in work for more than 30 years. A comparison of the current results with the initial designed parameters was made, and the power degradation after this long period of work was measured.

Effect of negative potential on the extent of PID degradation in photovoltaic power plant in a real operation mode

As part of the state's NY-Sun initiative, use of solar power in New York State has grown 575% from 2012 to 2015. The increase of solar power users in spite of the relatively high upfront cost of solar photovoltaic (PV) module installation is due to the high estimation of Return on Investment. However, most ROI estimation neglects the functional decline of efficiency of power generation over time (degradation rate). As the use of solar power is growing, the accurate prediction of power delivery over time in PV modules is important. The total power delivery to the electric system with a certain amount of solar radiation depends on both how efficiently a solar PV module converts sunlight into power and how this relationship changes over time. The Engineering Technology Department at Queensborough Community College has installed three major types of PV modules: monocrystalline, polycrystalline and thin film by four different manufacturers, on the southeast roof of the Technology Building. The main goal of this research is to estimate each type of solar PV module's degradation rate and compare the changes in the efficiencies with seven years of datasets in New York's climate. Knowing which type of solar PV module degrades slower or faster will provide crucial information to potential solar power users in New York.

The system operating costs and long-term reliability of the PV modules is significant in reducing the total lifetime cost of the PV system. In this context the diagnostic methods in identifying the degradation affecting PV array is important. Previous studies on degradation in PV modules showed that degradation leads to either decrease in shunt resistance or increase in series resistance of the PV module. With change in internal resistance of a PV array, the transient characteristics of array quantities (array voltage and current) may change. The effect of internal resistance of a PV array on transient characteristics was studied in this brief from the small signal model for a PV system with boost converter. The step responses for studying transient characteristics was obtained by implementing an extremum seeking control (ESC) based MPPT which injects a square wave dither signal into the duty ratio signal. The transient characteristics of array voltage signal were analyzed using suitable integral performance indices which helps in detecting degradation of PV array.

Seasonal effect of dust on the degradation of PV modules performance deployed in different climate areas

The effects of a sub-Saharan coastal climate on PV modules degradation was studied in this paper. A Mono and a polycrystalline-silicone solar PV module exposed in Dakar, dry and coastal climate, at the extreme West of Senegal was studied. As first inspection in this region, the electrical parameters of two PV modules A and B operated during about 10 years, are measured under standard testing condition (STC) and their I-V characteristics were fitted. The initial I-V characteristics was performed under real conditions and translated to STC and compared to the measured I-V characteristics at standard test conditions (STC) obtained in PV Laboratory after exposition. After the operating years, the main important parameters of the studied PV modules: short-circuit current ISC, open circuit voltage UOC, maximum power PMPP, nominal current IMPP and Voltage VMPP are evaluated and then compared to the initial parameters obtained during initial exposition to estimate their degradation.