Query: Commonly observed degradation in field-aged photovoltaic modules

Candidate papers:

abstract: Degradation leading to failure in photovoltaic modules follows a progression that is dependent on multiple factors, some of which interact causing degradation that is difficult to simulate in the lab. This paper defines observed degradation in field aged modules, including degradation of packaging materials, adhesional loss, degradation of interconnects, degradation due to moisture intrusion, and semiconductor device degradation. Additionally, this paper suggests that the onset and progression of degradation need to be studied to gain a more comprehensive understanding of module degradation rates and module failures.
author_names: Michael A Quintana

David L King

Thomas Joseph Mcmahon

Carl R Osterwald
title: Commonly observed degradation in field aged photovoltaic modules
venue: Conference Record of the Twenty Ninth IEEE Photovoltaic Specialists Conference, 2002.
year: 2002

abstract: Abstract Delamination and discoloration are the most commonly observed encapsulant degradations in crystalline silicon photovoltaic (PV) modules under field conditions. In this work, a comparative analysis of brown discoloration and front side grey appearing delamination of ethylene vinyl acetate (EVA) has been presented, to understand their basic effects and modes of degradation. For this purpose, both type of degraded EVA samples from field aged PV modules have been investigated, for finding the difference in their spectral response, chemical constituents, structural change, and impact on module electrical performance. These investigations have been performed using quantum efficiency (QE) measurement, Fourier transform infrared (FTIR) spectroscopy, X ray diffraction (XRD) and scanning electron microscopy (SEM) In addition, electrical analysis was performed using PSpice circuit simulator. The distinct effect of discolored and delaminated EVA degradations, on incident radiations was identified mainly in absorption and reflection loss respectively, under different wavelengths. Also, the impact of these degradations on module performance, due to mismatch loss within the module has been presented. The chemical constituent investigation, supported presence of delamination in grey degraded sample due to absence of interfacial adhesive agent, in contrast to discolored sample. Findings from the structural investigation, corroborated a decrease in crystalline behaviour of both degradations. Furthermore, impressions from etched silicon cell were observed only in delaminated sample, which can be the reason of its grey appearance and more reflection. This work highlights the comparative effects and impact of dominant EVA degradations in terms of their characteristic aspects, which can be instrumental in improvement of EVA formulation.
author_names: Roop Singh Meena

Sagarika Kumar

Rajesh Gupta
title: Comparative investigation and analysis of delaminated and discolored encapsulant degradation in crystalline silicon photovoltaic modules
year: 2020

abstract: Degradation is commonly observed in field aged PV modules due to corrosion of the photovoltaic ribbon. The reduced performance is caused by a loss of fill factor due to the high series resistance in the PV ribbon. This study aimed to mitigate the degradation by corrosion using five sacrificial anodes Al, Zn and their alloys to identify the most effective material to mitigate the corrosion of the PV ribbon. The corrosion behavior of the five sacrificial anode materials were examined by open circuit potential measurements, potentiodynamic polarization tests, and galvanic current density and potential measurements using a zero resistance ammeter. Immersion tests for 120 hours were also conducted using materials and damp heat test tests were performed for 1500 hours using 4 cell mini modules. The Al 3Mg and Al 3Zn 1Mg sacrificial anodes had a low corrosion rate and reduced drop in power, making then suitable for long term use. yo yag taeyanggwang modyuleseo taeyangjeonjireul yeongyeolhaejuneun inteokeonegteoro ribon soldeoro SnPbAgga sayongdoego, ogoe taeyanggwang baljeone janggigan noculsi ribonyi busigeuro inhan yeolhwaga heunhi gwancaldoenda. ireohan busighyeonsangeuro inhayeo ribongwa taeyangjeonjiyi jeobhabi yaghaejyeo jeobcogjeo hangi jeunggahago, ddohan ribon jaceyi jigryeol jeohangi jeunggahage doeeo taeyangjeonjiyi jeonab jeonryu gogseoneseo cungjinryul sonsilro culryeogi jeohadoen da. bon nonmuneseoneun ribonyi busigeul wanhwasikil su issneun bangbeobeuro hyisaengyanggeugbeobeul iyonghayeo sunsu alruminyum mic ayeon, alruminyum, ayeon geurigo mageunesyumyi habgeumeul iyonghan 5gaji hyisaengyanggeug sojaeyi busige yihan yeolhwa jeogameul yeonguhayeossda. jeongihwahagjeog bangbeobeuro hyisaengyang geug sojaeyi gaebanghoero jeonwiwa pyeswaehoero jeonwireul ceugjeonghayeossgo, potensiodainamig bungeug gogseoneul ceugjeonghago, yeongjeohangjeonryugyereul iyonghayeo ribongwa sojaeganyi galbanig jeonryureul ceugjeonghayeossda. ddohan, aseteusangwa, NaCle ribongwa hyisaengyanggeug sojaeyi bucag jeonhuyi cimjisiheomgwa 4sel minimodyulro jejaghan hu 1500sigan goongoseub siheom jeonhu culryeogeul pyeonggahayeossda. geu gyeolgwa Al 3Mgwa Al 3Zn 1Mgyi hyisaengyanggeug sojaega busigsogdoga neurigo, culryeogjeohareul jeogamsikil bbunman anira janggi anjeongseongedo hyogwajeogin geoseuro pyeonggadoenda.
author_names: Wonwook Oh

S I Chan
title: Corrosion mitigation of photovoltaic ribbon using a sacrificial anode
year: 2017

abstract: To identify the common degradation mechanism(s) between field aged photovoltaic (PV) modules and PV cells/modules exposed to artificial corrosive stress, the ac impedance associated with the corrosion in the front electrodes was analyzed in the individual PV cells laminated within the PV modules, fielded for 21 years. By evaluating the ac impedance together with the PV performance for these PV cells, we found that the short circuit current (Isc) remarkably decreased, depending on the expression and elevation of the ac impedance relevant to the front electrode corrosion. This Isc reduction can be explained by the formation of rectifying contacts to restrict the current conduction between the front electrodes and the associated silicon wafer. Since the Isc reduction was primarily observed in the PV cells with extensive loss of fill factor, we suggest that the power loss is induced by the gap formation underneath the front electrodes, followed by the emergence of rectifying contacts, even in the PV cells/modules degraded in field. The ac impedance parameters of the PV cells/modules could be a valuable predictor of the service lifetime of PV modules, as our findings in this study mean the equivalency of the failure attained by extended damp heat testing with that observed in the field.
author_names: Tadanori Tanahashi

Norihiko Sakamoton

Hajime Shibata

Atsushi Masuda
title: Corrosion Induced AC Impedance Elevation in Front Electrodes of Crystalline Silicon Photovoltaic Cells Within Field Aged Photovoltaic Modules
venue: IEEE Journal of Photovoltaics
year: 2019

abstract: Ethylene vinyl acetate (EVA) is the predominant encapsulant in crystalline silicon photovoltaic (PV) modules; however, its degradation is a subject of major concern, which causes significant power loss under field conditions. This article presents a comparison of EVA degradation in field aged PV modules with glass/backsheet (G/B) and glass/glass (G/G) architectures. Module level characterization included UV fluorescence imaging and I V measurements. Material analytical techniques, including colorimetry, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy, were performed to correlate the module performance parameters with EVA material properties. An intense EVA discoloration in G/G modules was observed, which was corroborated by higher module $I_{sc} and Pmax degradation rates compared with its counterpart G/B modules. Higher power degradation was accompanied by a significant increase in EVA crosslinking, vinyl acetate content, yellowness index, and presence of functional groups containing unsaturated moieties that are linked to degradation products of photothermal reaction, and a higher decrease in the degree of crystallinity. The absence of a polymeric backsheet in hermetically sealed G/G modules, which restricts photobleaching and enhances the entrapment of volatile acetic acid and other degradation by products, plays a major role in causing higher EVA degradation in G/G modules. This article concludes that EVA might have been a good choice of an encapsulant for the G/B modules over the decades, but it may prove to be an inappropriate choice for the G/G modules because of potential degassing, corrosion, and/or discoloration issues. Ionomers or polyester based encapsulants like polyolefins could be best suited for G/G modules as it appears to be a current trend in the industry.
author_names: Aesha Parimalbhai Patel

Archana Sinha

Govindasamy Tamizhmani
title: Field Aged Glass/Backsheet and Glass/Glass PV Modules: Encapsulant Degradation Comparison
venue: IEEE Journal of Photovoltaics
year: 2020

abstract: Degradation phenomena observed in field aged crystalline silicon photovoltaic modules include EVA browning, delamination between the glass encapsulant and the cell encapsulant interfaces, degradation of the anti reflective coating, corrosion of busbars and contacts, cracks, humidity ingress, etc. The type and severity of the defects observed vary significantly between cells, modules and installations as affected by a number of both internal and external parameters. This study presents mild to severe degradation effects observed in crystalline silicon PV modules operating outdoors for different periods of time and investigated through non destructive testing techniques including I V characterisation, UV fluorescence, IR thermography and Electroluminescence (EL) Imaging. The identification and diagnosis of defects and further correlation to the electrical degradation of the module is achieved through the complementary contribution of these techniques. Severe electrical degradation and mismatch between the cells are identified through IR thermography and EL imaging. Diagnosis of rather uniformly degraded modules is enhanced through EL Imaging by which shunts, higher resistance regions, cracks, broken metallization are identified, while the module may appear to operate reliably. Signs of early degradation are further diagnosed through UV fluorescence and EL Imaging, allowing to monitor the evolution of defects and evaluate module reliability.
author_names: Eleni Kaplani
title: Degradation in Field aged Crystalline Silicon Photovoltaic Modules and Diagnosis using Electroluminescence Imaging
year: 2016

abstract: The longevity of solar photovoltaic modules depends on the durability and reliability of their components, one of which is the solder bonds in interconnect ribbons. The solder joints experience stresses from thermal cycling and constant elevated temperatures (40 degC 70 degC) in regular field operation leading to thermo mechanical fatigue and intermetallic compound formation. To study the end of life wear out mechanisms and to obtain activation energy of solder bond degradation, two field aged modules from Arizona a 21 year old Solarex MSX60 module (with Sn62Pb36Ag2 at the solder joints) and an 18 year old Siemens M55 module (with Sn60Pb40 at the solder joints) underwent 800 and 400 modified thermal cycles, respectively. Using three heating blankets, each module had three temperature zones maintained at 85, 95, and 105 degC during the 15 min hot dwell time of the thermal cycle. Cell level series resistance data obtained from three temperature zones enabled the calculation of activation energy for solder bond degradation for the MSX60 and the M55 modules to be 0.12 eV and 0.35 eV, respectively. From each temperature zone in both modules, busbar solder samples were obtained, imaged through SEM, and analyzed with energy dispersive X ray spectroscopy. In the MSX60 module with traces of Ag in the solder material, phase segregation and growth were primarily observed at high temperatures. For M55 modules without Ag in the solder material, major phase segregation was observed in all temperature zones. The IMC thickness for both modules increased with increasing module temperature. The beneficial effect of Ag in solder material on mitigating solder bond degradation is presented.
author_names: Hamsini Gopalakrishna

Archana Sinha

Joe Carpenter

Sridhar Niverty

Nikhilesh Chawla

Dirk C Jordan

Govindasamy Tamizhmani
title: Activation Energy for End of Life Solder Bond Degradation: Thermal Cycling of Field Aged PV Modules
venue: IEEE Journal of Photovoltaics
year: 2020

abstract: Encapsulant discoloration, a commonly occurring and serious field degradation mode, can be replicated by exposing modules to UV light. Increasing the UV light intensity and the testing temperatures reduces the required testing time. Calculating activation energy using Arrhenius equation for the encapsulant discoloration requires short circuit current data (or yellowness index data) at multiple temperatures over significant time period. A method of simultaneously obtaining four temperatures in four photovoltaic modules in a single walk in accelerated UV weathering chamber which drastically reduces the required time and resources is presented. Field aged modules with visible encapsulant browning were selected for the accelerated testing to determine the wear out failure mechanisms rather than the early life and midlife failure mechanisms conventionally determined using fresh modules. These modules have been subjected to a very long UV exposure of 450 kWh operating at high temperatures. This work demonstrates that a fast, repeatable, and non contact UV fluorescence setup can be used in the accelerated testing programs and in powerplants as a standardized technique for an early encapsulant browning detection.
author_names: Hamsini Gopalakrishna

Archana Sinha

Jaewon Oh

Kshitiz Dolia

Sai Ravi Tatapudi

Govindasamy Tamizhmani
title: Novel Accelerated UV Testing of Field Aged Modules: Correlating EL and UV Fluorescence Images with Current Drop
venue: 2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC 34th EU PVSEC)
year: 2018

abstract: In this paper, degradation in field aged PV modules including degradation of interconnect, discoloration of encapsulant and hot spot have been observed and analyzed. From the results, photovoltaic module installed for 6 years shows around 16 drop of electrical properties due to the interconnect degradation and PV module passed 18 years has been found to drop of around 20 mainly by the encapsulant discoloration. Furthermore the difference between low and high temperature of PV array at hot spot goes up to 3 and it leads to interconnect degradation. On the other hands, the temperature difference was observed to be around 15 at the encapsulant discoloration spot of PV array.
author_names: Gihwan Kang

Gwonjong Yu

Hyung-Keun Ahn

Deukyoung Han
title: Consideration of Electrical Properties in Field aged Photovoltaic Module
year: 2004

abstract: Due to the vast expansion of photovoltaic (PV) module production nowadays, a great interest is shown in factors affecting PV performance and efficiency under real conditions. Particular attention is being given to degradation effects of PV cells and modules, which during the last decade are seen to be responsible for significant power losses observed in PV systems. This paper presents and analyses degradation effects observed in severely EVA discoloured PV cells from field aged modules operating already for 18 22 years. Temperature degradation effects are identified through IR thermography in bus bars, contact solder bonds, blisters, hot spots, and hot areas. I V curve analysis results showed an agreement between the source of electrical performance degradation and the degradation effects in the defected cell identified by the IR thermography. Finally, an algorithm was developed to automatically detect EVA discoloration in PV cells through processing of the digital image alone in a way closely imitating human perception of color. This nondestructive and noncostly solution could be applied in the detection of EVA discoloration in existing PV installations and the automatic monitoring and remote inspection of PV systems.
author_names: Eleni Kaplani
title: Detection of Degradation Effects in Field Aged c Si Solar Cells through IR Thermography and Digital Image Processing
year: 2012