Encapsulation of PV modules using ethylene vinyl acetate copolymer as a pottant: A critical review

The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150^TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed.     

Energy performance of water hybrid PV/T collectors applied to combisystems of Direct Solar Floor type

The integration of photovoltaic (PV) modules in buildings allows one to consider a multifunctional frame and then to reduce the cost by substitution of components. In order to limit the rise of the cell operating temperature, a photovoltaics/thermal (PV/T) collector combines a solar water heating collector and PV cells. The recovered heat energy can be used for heating systems and domestic hot water. A combination with a Direct Solar Floor is studied. Its low operating temperature level is appropriate for the operating conditions of the mono- or poly-crystalline photovoltaic modules which are selected in that study. However, for a system including a glass covered collector and localised in Mâcon area in France, we show that the annual photovoltaic cell efficiency is 6.8% which represents a decrease of 28% in comparison with a conventional non-integrated PV module of 9.4% annual efficiency. This is obviously due to a temperature increase related to the cover. On the other hand, we show that without a glass cover, the efficiency is 10% which is 6% better than a standard module due to the cooling effect.Moreover, in the case of a glazed PV/T collector with a conventional control system for Direct Solar Floor, the maximum temperature reached at the level of the PV modules is higher than 100 °C. This is due to the oversize of the collectors during the summer when the heating needs are null, i.e. without a heated swimming pool for example. This temperature level does not allow the use of EVA resin (ethylene vinyl acetate) in PV modules due to strong risks of degradation. The current solution consists of using amorphous cells or, if we do not enhance the thermal production, uncovered PV/T collector. Further research led to water hybrid PV/T solar collectors as a one-piece component, both reliable and efficient, and including the thermal absorber, the heat exchanger and the photovoltaic functions.     

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.     

Chemical treatment of crystalline silicon solar cells as a method of recovering pure silicon from photovoltaic modules

Photovoltaic technology is used worldwide to provide reliable and cost-effective electricity for industrial, commercial, residential and community applications. The average lifetime of PV modules can be expected to be more than 25 years. The disposal of PV systems will become a problem in view of the continually increasing production of PV modules. These can be recycled for about the same cost as their disposal.Photovoltaic modules in crystalline silicon solar cells are made from the following elements, in order of mass: glass, aluminium frame, EVA copolymer transparent hermetising layer, photovoltaic cells, installation box, Tedlar^® protective foil and assembly bolts. From an economic point of view, taking into account the price and supply level, pure silicon, which can be recycled from PV cells, is the most valuable construction material used.Recovering pure silicon from damaged or end-of-life PV modules can lead to economic and environmental benefits. Because of the high quality requirement for the recovered silicon, chemical processing is the most important stage of the recycling process. The chemical treatment conditions need to be precisely adjusted in order to achieve the required purity level of the recovered silicon. For PV systems based on crystalline silicon, a series of etching processes was carried out as follows: etching of electric connectors, anti-reflective coating and n-p junction. The chemistry of etching solutions was individually adjusted for the different silicon cell types. Efforts were made to formulate a universal composition for the etching solution. The principal task at this point was to optimise the etching temperature, time and alkali concentration in such a way that only as much silicon was removed as necessary.     

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.     

Ten years outdoor operation of silicon based photovoltaic modules at central latitude of Japan

For the estimation of energy output from photovoltaic (PV) modules, considering the impact of degradation is essential. In this study, the longtime outdoor performance of various types of silicon-based PV modules [single crystalline Si (sc-Si), multi crystalline Si (mc-Si), amorphous Si (a-Si), a-Si/micro crystalline Si tandem, and a-Si/a-SiGe/a-SiGe three-stack (3-stack)] which were installed at the same outdoor exposure condition in Shiga Prefecture, Japan were investigated using Performance Ratio (PR) as an index of performance of PV modules for ten years from 2000 to 2009. Yearly PR and monthly PR were analyzed and degradation rates (DR) were calculated. The DR was different on the kinds of PV modules from 0.404 to 3.51%/year. The a-Si PV module showed the largest DR and the 3-stack PV module had the least trend to degrade. The analysis of the monthly DR indicated that the high DR of the a-Si PV module was due to the quite large DR in summer, whereas the monthly DR of sc-Si and mc-Si PV modules did not differ much from each other throughout the years.     

Towards 50 years lifetime of PV panels laminated with silicone gel technology

A silicone gel lamination technology of PV panels has been developed and gel lamination apparatus with an annual production capacity of 1 MW_p has been designed and manufactured. Silicone gel laminated c-Si PV panels were prepared and tested at 3.5 times concentrated solar radiation in the UV chamber. Negligible corrosion of silicone gel laminated PV panels was observed in comparison with EVA laminated panels. In contrast to EVA-laminated panels the transparency reduction induced by UV radiation in silicone gel lamination is very small. Production of silicone gel laminated PV panels with 50 years lifetime could be achievable because of the strongly reduced corrosiveness which is main source of failures in commercial PV panels.Photodegradation of some components of PV systems was observed in the past, for example (Reda, 2007, Daliento and Lancellotti, 2010).     

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.     

Feasibility of solar tracking systems for PV panels in hot and cold regions

Solar tracking systems would probably increase the efficiency of a PV module, but when and where. There are many factors that affect the performance of PV panels, especially crystalline silicon panels, e.g. overheating due to excessive exposure to solar irradiance in a hot climate as in Sunbelt countries. So, it could be the case that a tracking system is not necessary for a Sunbelt country. The objective of this research is to determine mathematically the performance of a PV panel as a function of tracking the sun and the operating conditions. The used mathematical model is validated experimentally and then applied for several environments, i.e. hot as well as cold regions. It has been found that the gain in electrical energy from tracking the sun is about 39% in case of a cold city as Berlin, Germany. While the gain in energy does not exceed 8% in case of a hot city as Aswan, Egypt, due to overheating of the PV panels. However, if the energy needed for running the tracking system, which ranges from 5% to 10% of the energy generated, is included in this analysis then tracking the sun will not be feasible in hot countries.     

Secular degradation of crystalline photovoltaic modules

The performance of crystalline photovoltaic (PV) modules has been measured once a year in field exposure. Their maximum power output (P_max) decreases 4.8% for single-crystalline PV modules and 2.0% for the poly-crystalline case in comparison with their initial P_max at ex-work after five years' field exposure.This paper describes the secular degradation of crystalline PV modules.     

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.).     

Assesment of grid-connected photovoltaic systems in the Kuwaiti climate

Grid-connected photovoltaic (PV) systems is one of the most promising applications of PV systems. Till now, no detailed studies have been carried out to assess the potential of grid-connected systems in Kuwait. This work investigates the feasibility of implementing grid-connected PV systems in the Kuwaiti climate. The proposed system consists of crystalline solar modules mounted on the building roof and an inverter to convert PV dc output to ac voltage. The building receives electricity from both the PV array and the utility grid. In this system, the load is the total electrical energy consumption in the building.The objective of this work is to examine the performance as well as the economic feasibility of grid-connected PV systems in the Kuwaiti climate. A program is written to evaluate the performance as well as the economic feasibility of such systems in Kuwait. The input to the program is the weather data for Kuwait, time dependent building loads, as well as the utility rates for Kuwait. Weather data generator subroutine included in the program is used to generate hourly weather conditions from the monthly average values of daily radiation on horizontal surface, and ambient temperature available for Kuwait. The five-parameter PV model, which is applicable to both crystalline and amorphous PV modules, is used to determine the performance of the solar modules used in this study.The transient simulation program ( ) is used to link the components of the grid-connected PV system together. The inverter efficiency is represented as a linear function of input power. In this case, it is assumed that the AC output from the system will never be greater than the building load. Electricity tariffs will have an important impact on the cost-effectiveness of the system studied. The tariff used for electric utility is a flat rate per unit kWh of electrical energy. Simulations of the proposed system were carried out over the academic year.The building examined in this study is a flat roof building with a single story. The building roof area is large enough so that the PV arrays can be spaced widely to minimize shading losses. Different array slopes, and azimuth angles were studied to maximize the annual energy generated by the PV modules. Finally, the economic feasibility of grid-connected PV systems in Kuwait are examined.     

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.     

退役晶体硅光伏组件的回收技术综述

自2020年起的未来10年,大规模的光伏组件将要退役,如何经济高效地处理废旧光伏组件将成为一大难题。晶体硅光伏组件中的材料种类较多,也难以分离,而且所得到的回收材料价值不高,低于组件回收的成本。但是,若退役晶体硅光伏组件处理不当,将会对生态环境造成极端恶劣的影响。晶体硅光伏组件在土壤中很难降解,如果只是简单的掩埋处理,将会对土壤环境造成破坏,所以回收退役晶体硅光伏组件势在必行。梳理了目前世界范围内回收退役晶体硅光伏组件的技术,并通过不同维度的比较寻求效率高、收益好,并具有发展潜力的退役晶体硅光伏组件回收技术。     

一种多功能光伏发电系统的可行性研究

通过在光伏组件的背面连接了一个热电转换模块,形成一个光伏一热电混合模块,从而将光伏组件工作过程中产生的废热转换成电能的同时又降低了光伏组件的温度,进而提高了光电转换效率。将光伏一热电模块与百叶有效结合,从而实现了室内采光、通风及节约空间等多种功能。同时,为了提高光伏组件的入射太阳辐射,引入了可调节的抛物型双面聚焦板,减少了太阳能电池板的面积,从而减少了太阳能发电的成本。     

Review of modern methods and technologies for using of solar energy in the operation of anaerobic digestion systems

The article presents various methods and technologies for using of solar energy in anaerobic bioconversion systems. Various methods of convertion of solar radiation are consistently considered – from its direct use to photovoltaic, thermal, photovoltaic thermal and concentrating. Schemes for introducing solar energy converters into anaerobic bioconversion systems, as well as various solar radiation converters for heat and electricity supply of anaerobic bioconversion systems, are proposed. As power generating components in the article also discusses photovoltaic modules with an extended rated power period, photovoltaic thermal roofing panels with a two-component polysiloxane compound, thermal and photovoltaic thermal solar roofing panels, air-cooled photovoltaic thermal siding panel and concentrator solar photovoltaic thermal module with high-voltage matrix photovoltaic converters. The proposed schemes of systems and design of solar modules will ensure a reduction in the use of thermal energy from the produced gas for power supply for the own needs of anaerobic bioconversion systems, which will make them cheaper and more efficient in operation.     

Estimation of irradiance and outdoor performance of photovoltaic modules by meteorological data

Three environmental factors of irradiance, solar spectral distribution and module temperature greatly affect the performances of photovoltaic (PV) modules. If the environmental factors can be estimated by basic meteorological data (BMD) announced by an official organization in various areas, the performances of PV modules can be estimated easily. In this study, a relationship between the environmental factors and the BMD was analyzed. The performances of Si-based (crystalline Si and thin-film Si) PV modules were estimated by the relationship. As a result, errors between the estimation and actual performances in the crystalline Si and thin-film PV modules were within 1.88% and 0.58% in Kusatsu city, Japan (34°58′N, 135°57′E). This methodology can be useful for rating the performance of PV modules at various areas.     

Spatial and orientational distribution of cracks in crystalline photovoltaic modules generated by mechanical load tests

Cracks in crystalline silicon solar cells influence the photovoltaic (PV) module power output in accelerated aging tests. A detailed insight into the formation of cracks offers the potential to optimize the PV module design in order to reduce the risk of power degradation in its lifetime. In this paper we present a statistical analysis on the crack formation in 27 crystalline silicon PV modules caused by a standard mechanical load test according to IEC 61215 10.16. The criticality of cracks depends strongly on the crack orientation, therefore we analyze both the spatial distribution of cracks and its dependence on the orientation of the cracks in the tested PV modules. We find that 50% of the damaged cells are cracked parallel to the busbars, which is a crack orientation with high potential impact on the power output of the PV module. A simplified numerical analysis is used to give an explanation for the statistical data and we propose a strategy for the reduction of the crack criticality.     

Flat roof integration of a-Si triple junction modules laminated together with flexible polyolefin membranes

In BIPV design (Building Integrated PV) with crystalline silicon (c-Si) solar cells, ventilation is important in order to keep cells as cool as possible. To allow good ventilation it is therefore generally preferable to mount the modules separated from the existing roof. In the case of sloped roofs, the modules are superimposed onto the existing roof and for flat roofs separated tilted mounting structures designed to withstand wind loads are used instead, but both are not real building integrations.In this paper we analyse the behaviour and the energy yield of a 15.36 kWp PV system based on flexible triple junction amorphous silicon modules laminated together with a single ply roofing system.The PV plant has been integrated on a flat roof of a professional school located south of Switzerland. A significant part of the data analysis is done in comparison with three small open-rack plants (reference plants) installed near the integrated plant.An important result was that the thermally insulated nearly horizontal modules showed temperatures higher than for modules mounted on an open-rack structure, especially for sunny days. This created higher power losses due to negative temperature coefficients. On the other hand, the higher temperature reached the level where the main degradation mechanism of a-Si modules could be reversed and better thermal annealing could be observed. This conclusion was arrived at after a direct performance comparison of the thermally insulated plant and the open-rack a-Si reference plant, which has the same module and orientation as the main plant.In order to better understand the thermally insulated nearly horizontal plant behaviour, we analysed and quantified the irradiation difference and optical losses with respect to a 20° tilted open-rack c-Si power plant. Optical losses for nearly horizontal modules were significant during the winter, partially affecting their low performance.As a main result, the final energy yield of the thermally insulated a-Si plant was almost comparable to a 20° tilted open-rack c-Si power plant, despite the lower irradiance and higher reflection losses with respect to the latter.Accordingly, compared to c-Si modules, the a-Si technology represents a better choice for thermal insulated BIPV.     

Monitoring current–voltage characteristics and energy output of silicon photovoltaic modules

Photovoltaic (PV) system designers use performance data of PV modules to improve system design and make systems more cost effective. The collection of this valuable data is often not done due to the high costs associated with data acquisition systems. In this paper, we report on the design of a low-cost current–voltage (I–V) measuring system used to monitor the I–V characteristics of PV modules. Results obtained from monitoring seven crystalline silicon modules between October 2001 and November 2002 are presented and discussed. Results obtained also show the value of being able to continuously monitor the current–voltage characteristics of PV modules.