Non-destructive degradation analysis of encapsulants in PV modules by Raman Spectroscopy

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 in the encapsulant.     

Thermal stability of slow and fast cure EVA encapsulant material for photovoltaic module manufacturing process

Ethylene vinyl acetate (EVA) is a copolymer encapsulant used as an interlayer in the industrial photovoltaic module encapsulation process. EVA serves to provide the functions of structural support, electrical isolation, physical isolation/protection and thermal conduction for the solar cell circuit. This paper focuses on thermal properties of slow and fast cure EVA encapsulant material. Phase transition and thermal stability parameters of uncured EVA materials have been studied by employing thermo gravimetric analysis, thermal differential analysis and differential scanning calorimetric. EVA fast cure encapsulant material exhibits superior thermal stability in the range of operational cell temperature.     

Investigation of the degradation of a thin-film hydrogenated amorphous silicon photovoltaic module

The degradation of a thin-film hydrogenated single-junction amorphous silicon (a-Si:H) photovoltaic (PV) module has been studied. We investigated the different modes of electrical and physical degradation of a-Si:H PV modules by employing a degradation and failure assessment procedure used in conjunction with analytical techniques, including, scanning electron microscopy (SEM) and thermogravimetry. This paper reveals that due to their thickness, thin films are very sensitive to the type of degradation observed. Moreover, this paper deals with the problems associated with the module encapsulant, poly(ethylene-co-vinylacetate) (EVA). The main objective of this study was to establish the influence of outdoor environmental conditions on the performance of a thin-film PV module comprising a-Si:H single-junction cells.     

Photothermal stability of encapsulated Si solar cells and encapsulation materials upon accelerated exposures

We have conducted a series of accelerated exposure test (AET) studies for various samples of crystalline-Si (c-Si) and amorphous-Si (a-Si) cells that were encapsulated with different superstrates, pottants, and substrates. Transmittance, fluorescence, color indices, impedance spectroscopy, laser optical beam induced current (OBIC), and light and dark current–voltage (I–V) measurements were used to characterize the samples. Nonuniform browning patterns of ethylene vinyl acetate (EVA) pottants were observed for glass/EVA/glass-encapsulated c-Si cell samples under solar simulator exposures at elevated temperatures. The EVA discolored gradually into a yellow–brown color when exposed under 7.5 ultraviolet (UV) suns at a black panel temperature (BPT) of 85°C, and very rapidly into a dark brown color when exposed under 9.0 UV suns at a BPT of 145°C. The latter conditions also caused extensive delamination of a polyolefin-based thermoplastic pottant laminated between two borosilicate plates. No visible color change of EVA could be observed for the c-Si cell samples heated in an oven at 85°C or exposed under 1.2 UV suns at BPT=60–65°C or 80–85°C. Under 1.2 UV suns exposure at a BPT of 60–65°C, the thin layers of EVA or silicone in the lightweight c-Si cell samples, which were laminated in a polymer/solar cell/polymer configuration with Tedlar or Tefzel films, did not discolor because of photobleaching reactions. In comparison, the polyester or nylon superstrate films turned yellow on laminates of polymer/a-Si/polymer minimodules, and significant delamination was observed for the polyester/EVA layers. For all c-Si cell samples tested, irregular changes in the I–V parameters were observed that could not be attributed only to transmittance changes of the superstrate/pottant layers. Under UV-transmitting polymer superstrate films, current/efficiency losses were greater for the c-Si and a-Si cells that were laminated with silicone-type adhesives than with EVA or polyethylene pottants.     

Evaluation of the aging behavior of ethylene copolymer films for solar applications under accelerated weathering conditions

Ethylene copolymers based on acrylic acids and acrylates are an interesting alternative to ethylene(vinylacetate) (EVA) for photovoltaic (PV) encapsulation. These materials provide similar or better mechanical and optical properties and a slightly better aging behavior, but without the formation of corrosive acetic acid during aging, which is particularly of importance in PV applications. The focus of the research work was to evaluate and screen the aging behavior of ethylene copolymers containing different types of comonomers for solar applications. To investigate the intrinsic weathering behavior of the materials, unstabilized films with comonomer contents around 10% were exposed to temperature, humidity and solar radiation. Special attention was given to the optical and mechanical properties. All investigated films showed high transparency in the solar range with hemispheric transmittance values above 91%. Regarding mechanical properties, the ethylene copolymer films exhibited a highly ductile behavior and high flexibility. Similar degradation behavior could be observed for all investigated films. Due to formation of chromophoric degradation products, yellowing could be observed and hemispheric transmittance values dropped slightly to values between 88.5 and 90.5%. The unstabilized films showed significant embrittlement due to weathering. After 750 h of weathering both strain-at-break and stress-at-break values of all ethylene copolymer films dropped significantly below 50% of the initial values.     

Optical degradation of long-term, field-aged c-Si photovoltaic modules

The optical degradation induced by long-term (about 15 years) field exposure on c-Si photovoltaic modules belonging to the large-scale Delphos ENEA PV plant, located in Manfredonia (South of Italy), was investigated by making comparative reflectance measurements on the exposed modules, after their dismounting and cleaning, and on the original, unexposed counterparts. Four types of module fabrication technologies were analyzed: Helios single-Si, Pragma single-Si, Pragma multi-Si and Ansaldo multi-Si. Siemens multi-Si modules, of recent technology and exposed for 5 years, were taken as reference. The electrical loss measured for the single PV generators of the Delphos plant, each corresponding to a particular module technology, after a monitoring period of about 10 years, resulted to range between 11–22% for the output power and 9–14% for the output current. The aging effects on the dismounted and cleaned modules appeared as the discoloration of ARC layer, particularly at the center of the cells, and as the formation of stains distributed over the cell surface, likely due to the browning of the EVA. The spectral measurements of the total hemispherical reflectance, carried out under direct light at near-normal incidence, showed that the discoloration of ARC is associated to a decrease of the reflectance in the blue region (400–500 nm), and a resulting levelling of the spectral reflectance curves. The spectrally integrated measurements of reflectance carried out at diffuse white light, on the other hand, have provided evidence of an increase of the total hemispherical reflectance for exposed modules, particularly marked for the multi-Si modules, which correlates quite well with the extent of current loss measured on the single PV generators of Delphos plant.     

不同技术类型光伏组件的户外发电性能及衰减分析

对在广东省顺德地区(属于亚热带季风气候)运行的异质结(HIT)光伏组件、铜铟镓硒(CIGS)薄膜光伏组件、碲化镉(CdTe)薄膜光伏组件这3种不同技术类型的光伏组件的户外发电性能进行了比较,并对这3种光伏组件的功率衰减情况进行了定量分析。截至2019年12月,上述3种光伏组件的户外累计运行时间长达12年,其室内Ⅰ-Ⅴ特性的测试结果表明,HIT光伏组件、CIGS薄膜光伏组件、CdTe薄膜光伏组件的年均功率衰减率分别为0.32%、0.84%和1.72%。此外,采用系统能效比(performance ratio,PR)和PVUSA能效评定2种方法对3种光伏组件实证系统的发电性能进行了评估,2种评估方法的结果基本一致,均为HIT光伏组件实证系统的功率衰减最小;而造成CdTe光伏组件实证系统发电量损失较大的主要原因在于CdTe薄膜光伏组件本身的功率衰减。     

Sinusoidal spectral correction for high precision outdoor module characterization

We present the results of experiments which demonstrate that a sinusoidal variation in the long-term, STC-corrected, outdoor performance of PV modules is caused by seasonal spectral changes in the received sunlight. This variation may be factored out to increase the precision of outdoor studies. We use this result (a) to quantify the rate of EVA degradation observed in the Negev desert under natural 1-sun conditions and (b) to identify a principal source of the “summer recovery” observed in modules of amorphous silicon cells.     

Equilibrium thermal characteristics of a building integrated photovoltaic tiled roof

Photovoltaic (PV) modules attain high temperatures when exposed to a combination of high radiation levels and elevated ambient temperatures. The temperature rise can be particularly problematic for fully building integrated PV (BIPV) roof tile systems if back ventilation is restricted. PV laminates could suffer yield degradation and accelerated aging in these conditions. This paper presents a laboratory based experimental investigation undertaken to determine the potential for high temperature operation in such a BIPV installation. This is achieved by ascertaining the dependence of the PV roof tile temperature on incident radiation and ambient temperature. A theory based correction was developed to account for the unrealistic sky temperature of the solar simulator used in the experiments. The particular PV roof tiles used are warranted up to an operational temperature of 85 °C, anything above this temperature will void the warranty because of potential damage to the integrity of the encapsulation. As a guide for installers, a map of southern Europe has been generated indicating locations where excessive module temperatures might be expected and thus where installation is inadvisable.     

Estimation of photovoltaic module yearly temperature and performance based on Nominal Operation Cell Temperature calculations

The simulation of module temperature from Nominal Operation Cell Temperature (NOCT) is widely used to easily estimate module performance along the year. In this context, it is important to determine this parameter in a reliable way, as it is used to compare the performance of different module designs and can influence system predictions. At present there are several international standards that indicate the method to calculate NOCT in crystalline and thin-film terrestrial photovoltaic modules. This work presents the results obtained when applying these standards to different types of PV modules, including glass–glass and glass–tedlar structures, crystalline and thin-film technologies, and some special module designs for building integration applications. NOCT values so calculated have been used to estimate the yearly module temperature and performance for different orientations and tilted angles, analysing temperature influence in these estimations. Possible error sources that could bring about erroneous values of NOCT are also analysed.     

Adhesional shear strength and surface analysis of a PV module deployed in harsh coastal climate

Adhesional shear strength and chemical composition at the Si/EVA interface of samples extracted from a PV module manufactured by a major manufacturer using slow-cure EVA and deployed in the hot and humid climate at Cocoa, FL were studied. Precipitation of sodium from glass superstrate and ambient, and phosphorous from dopant glass reduced adhesional strength at Si/EVA interface to 35% of that in new modules. Presence of tin at this interface has also been attributed to solder-bond corrosion by moisture and impurities Na and P. It is interesting to point out that in this case, corrosion has occurred prior to delamination.     

Early degradation of silicon PV modules and guaranty conditions

The fast growth of PV installed capacity in Spain has led to an increase in the demand for analysis of installed PV modules. One of the topics that manufacturers, promoters, and owners of the plants are more interested in is the possible degradation of PV modules. This paper presents some findings of PV plant evaluations carried out during last years. This evaluation usually consists of visual inspections, I-V curve field measurements (the whole plant or selected areas), thermal evaluations by IR imaging and, in some cases, measurements of the I-V characteristics and thermal behaviours of selected modules in the plant, chosen by the laboratory. Electroluminescence technique is also used as a method for detecting defects in PV modules. It must be noted that new defects that arise when the module is in operation may appear in modules initially defect-free (called hidden manufacturing defects). Some of these hidden defects that only appear in normal operation are rarely detected in reliability tests (IEC61215 or IEC61646) due to the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV modules, power inverter influence, overvoltage on wires, etc.).     

Calculation of the PV modules angular losses under field conditions by means of an analytical model

Photovoltaic (PV) modules in real operation present angular losses in reference to their behaviour in standard test conditions, due to the angle of incidence of the incident radiation and the surface soil. Although these losses are not always negligible, they are commonly not taken into account when correcting the electrical characteristics of the PV module or estimating the energy production of PV systems. The main reason of this approximation is the lack of easy-to-use mathematical expressions for the angular losses calculation. This paper analyses these losses on PV modules and presents an analytical model based on theoretical and experimental results. The proposed model fits monocrystalline as well as polycrystalline and amorphous silicon PV modules, and contemplates the existence of superficial dust. With it angular losses integrated over time periods of interest can be easily calculated. Monthly and annual losses have been calculated for 10 different European sites, having diverse climates and latitudes (ranging from 32° to 52°), and considering different module tilt angles.     

Analysis of thermal and electrical performance of semi-transparent photovoltaic (PV) module

Building-integrated PhotoVoltaic (BIPV) is one of the most fascinating PV application technologies these days. To apply PV modules in buildings, various factors should be considered, such as the installation angle and orientation of PV module, shading, and temperature. The temperature of PV modules that are attached to building surfaces especially is one of the most important factors, as it affects both the electrical efficiency of a PV module and the energy load in a building. This study investigates the electrical and thermal performance of a semi-transparent PV module that was designed as a glazing component. The study evaluates the effects of the PV module's thermal characteristics on its electrical generation performance. The experiment was performed under both Standard Test Condition (STC) and outdoor conditions. The results showed that the power decreased about 0.48% (in STC with the exception of the temperature condition) and 0.52%(in outdoor conditions, under 500 W/m²) per the 1 °C increase of the PV module temperature. It was also found that the property of the glass used for the module affected the PV module temperature followed by its electrical performance.     

废弃光伏组件回收处理政策的研究

对废弃光伏组件进行回收处理有助于减轻环境负担、缓解资源短缺的压力,且可以保障光伏产业的绿色发展。从全球范围来看,产业化应用废弃光伏组件回收处理技术尚不成熟,目前仅有欧盟建立了针对废弃光伏组件回收处理的完整管理制度。我国对于废弃电器电子产品回收处理已有完善的政策体系,但还未将废弃光伏组件纳入其中。对欧盟关于废弃光伏组件回收处理的相关政策进行了研究,并对我国废弃电器电子产品回收处理管理政策进行了分析,在此基础上,提出了我国废弃光伏组件回收处理的政策建议。     

Seasonal variation analysis of the outdoor performance of amorphous Si photovoltaic modules using the contour map

The effects of module temperature (T_mod) and spectral irradiance distribution on the outdoor performance of amorphous Si (a-Si) photovoltaic (PV) modules were investigated using contour maps. Compared to PV modules based on crystalline Si, such as single-crystalline Si (sc-Si) and multicrystalline Si, a-Si PV modules exhibit complex behavior with seasonal variation. In this study, we statistically analyzed the outdoor performance of a-Si and sc-Si PV modules. The influence of environmental factors on outdoor performance of a-Si PV modules was analyzed for two seasons, spring and autumn, in which the data periods had nearly the same average T_mod and integrated irradiation. The outdoor performance of the a-Si PV module depends on both temperature history and light-induced degradation.     

Outdoor testing of PV module temperature and performance under different mounting and operational conditions

Outdoor performance of photovoltaic (PV) modules primarily depends on the instantaneous plane-of-array irradiance (G_poa) and PV module temperature (T_pv). T_pv can be estimated from the ambient temperature (T_amb) and the G_poa as T_pv=T_amb+k_TG_poa. The coefficient k_T depends strongly on the way the PV module is mounted (open rack, ventilated or unventilated roof mounting, etc.), wind speed and also on the module type. In the presented paper, open rack mounted and unventilated roof integrated cases of PV module installation are experimentally and theoretically examined. Linear relationship with k_T is upgraded with a nonlinear one based on the energy balance model and measured data. Nevertheless, T_pv is also affected by the module’s regime of operation. The T_pv dependency on different regime of operation (open-circuit and maximum power point tracking) for two types of PV modules in two regimes is reported. Differences are discussed in light of energy balance equation within thermal management, where impact of the PV module conversion efficiency on T_pv is also shown.     

Comparative study of performance degradation in poly- and mono-crystalline-Si solar PV modules deployed in different applications

Data on long-term performance and degradation of field-aged solar photovoltaic modules is widely recognized as necessary for continued technological improvement and market confidence. It is also important that such research should cover various geographical regions of the globe. This paper presents a study on twenty-nine (29) crystalline silicon modules deployed in grid-connected, battery-charging and water-pumping applications. The modules, installed at six different locations in Ghana were aged between 6 and 32 years. Peak power (P_max) losses ranged from 0.8%/year – 6.5%/year. The P_max losses were dominated by losses in fill factor (FF) and short-circuit current (I_sc). Visually observable defects are also reported.     

单面和双面单晶硅光伏组件的发电性能实证

针对p型PERC单面单晶硅光伏组件和n型双面单晶硅光伏组件,利用光伏组件户外实证测试系统,分析了2016年12月15日~2018年7月20日期间,上海市嘉定区某屋顶的地面采用白板背景时双面和单面组件,以及水泥背景时双面组件的等效发电时长,并对白板背景和水泥背景时双面组件较单面组件的发电量增益情况进行了分析;计算了组件的PR值;分析了阴天和晴天时组件最大输出功率与组件背板温度、太阳辐照度和环境温度的关系;最后对比了单面和双面组件运行13个月后的衰减值。该实证结果为单面和双面组件的户外实证发电性能提供了数据支撑,并对双面组件较单面组件的发电量增益情况进行了有效证明。     

Determination of thermal properties of crosslinked EVA encapsulant material in outdoor exposure by TSC and DSC methods

Apart from chemical structure, thermal properties of polymers depend mainly on polymer morphology, which is affected by the processing conditions. Outdoor exposure of the materials leads to changes in polymer morphology. The main objective of this experimental investigation was to better understand the changes due to thermal transitions and the molecular organizations of the crosslinked EVA encapsulant material after aging in outdoor exposure. The thermal properties of unaged and aged EVA encapsulant material were measured by thermal analysis methods as TSC and DSC. For the aged EVA samples, the distinctive feature of these results is that there are two different endothermic processes due to the recrystallization phenomenon. Furthermore, the difference of the magnitude of peak current by TSC technique suggests increased crosslinking exposure occurring selectively in the high temperature phase as a result of outdoor exposure.