Crystalline Silicon Photovoltaic Modules Research Articles

Effect of glass phase on solder joint reliability in crystalline silicon photovoltaic modules

The reliability of solder joints on Ag metallization electrodes is one of important factors that affect the service lifetime of crystalline silicon photovoltaic (PV) modules. In this article we show the effect of glass phase in Ag pastes on solder joint reliability. With peeling test of soldered samples after heat storage at 150 °C for various durations, we observed that with the increase of aging time, the fracture of peeled PV ribbons gradually extended inwards to Ag/Si interface, and there was remarkable distinction in the thermal endurance of solder joints as different glass frits were used in Ag metallization process. This indicates that the erosion of glass phase by solder is primary cause of the aging of solder joints, and this erosion mechanism depends on the glass phase composition. In terms of Bi containing glass that is generally adopted in the most commercial Ag pastes, we found that the Sn/Pb alloy solder can easily reduce Bi cations so as to destroy the glass network structure, making the Ag/Si interconnection to fail.

Relationship between cross-linking conditions of ethylene vinyl acetate and potential induced degradation for crystalline silicon photovoltaic modules

In this study, we investigated the relationship in crystalline silicon (c-Si) photovoltaic (PV) modules between the cross-linking level of copolymer of ethylene and vinyl acetate (EVA) as the encapsulant and the degree of degradation due to potential induced degradation (PID) phenomenon. We used three methods for the determination of cross-linking level of EVA: xylene method, which is one of the solvent extraction methods (SEM), curing degree by differential scanning calorimetry (DSC), and viscoelastic properties by dynamic mechanical analysis (DMA). The results indicate that degradation of PV modules by PID test depends on the cross-linking level of EVA. The PV modules encapsulated by EVA with higher cross-linking level show lower degradation degree due to PID phenomenon. Also we showed that EVA with higher cross-linking level tended to be higher volume resistivity. This tendency is similar to that for electrical resistance value during the PID test. The PID test was also done by changing thickness of EVA between front cover glass and c-Si with the same cross-linking level. The PV modules encapsulated by thicker EVA between front cover glass and c-Si cell show lower degradation by PID. From these results, the PV modules encapsulated by EVA with higher cross-linking level, higher volume resistivity and increased thickness would be tolerant of PID phenomenon.

Fault identification in crystalline silicon PV modules by complementary analysis of the light and dark current–voltage characteristics

AbstractThis article proposes a fault identification method, based on the complementary analysis of the light and dark current–voltage (I–V) characteristics of the photovoltaic (PV) module, to distinguish between four important degradation modes that lead to power loss in PV modules: (i) degradation of the electrical circuit of the PV module (cell interconnect breaks; corrosion of the junction box, module cables, and connectors); (ii) mechanical damage to the solar cells (cell microcracks and fractures); (iii) potential‐induced degradation (PID) sustained by the module; and (iv) optical losses affecting the module (soiling, shading, and discoloration). The premise of the proposed method is that different degradation modes affect the light and dark I–V characteristics of the PV module in different ways, leaving distinct signatures. This work focuses on identifying and correlating these specific signatures present in the light and dark I–V measurements to specific degradation modes; a number of new dark I–V diagnostic parameters are proposed to quantify these signatures. The experimental results show that these dark I–V diagnostic parameters, complemented by light I–V performance and series‐resistance measurements, can accurately detect and identify the four degradation modes discussed. Copyright © 2015 John Wiley & Sons, Ltd.

Interlaboratory Study to Determine Repeatability of the Damp-Heat Test Method for Potential-Induced Degradation and Polarization in Crystalline Silicon Photovoltaic Modules

To test reproducibility of a technical specification under development for potential-induced degradation (PID) and polarization, three crystalline silicon module types were distributed in five replicas each to five laboratories. Stress tests were performed in environmental chambers at 60 °C, 85% relative humidity, 96 h, and with module nameplate system voltage applied. Results from the modules tested indicate that the test protocol can discern susceptibility to PID according to the pass/fail criteria with acceptable consistency from lab to lab; however, areas for improvement are indicated to achieve better uniformity in temperature and humidity on the module surfaces. In the analysis of variance of the results, 6% of the variance was attributed to laboratory influence, 34% to module design, and 60% to variability in test results within a given design. Testing with the additional factor of illumination with ultraviolet light slowed or arrested the degradation. Testing at 25 °C with aluminum foil as the module ground was also examined for comparison. The foil, as tested, did not itself achieve consistent contact to ground at all surfaces, but methods to ensure more consistent grounding were found and proposed. The rates of degradation in each test are compared, and details affecting the rates are discussed.

A study on soldering characteristics of laser tabbing system for crystalline silicon photovoltaic module production

The most significant task in the solar cell industry today is to minimize the cost of solar cell development, thereby establishing grid parity early. One way to achieve this goal is to reduce the thickness of silicon solar cell, which would subsequently result in reduction in raw silicon material costs. The most commonly used tabbing process in solar cell production today is the heating bar process. This process utilizes electric heating bars to heat the ribbons on solar cells. In this study, a laser tabbing machine was developed to overcome the problems of tabbing process of heating bar technique for a thin crystalline silicon solar cell. An electric test and peeling test were executed on soldering ribbon on solar cells. The results indicate that the bonding force of ribbon does not affect electrical output of the solar cell. The electric power of soldered solar cell was decreased around 5% in output as compared to the original unsoldered solar cell. The electric powers of the laser soldered module and the heating-bar soldered module were very close. The decline in efficiency of both modules was about 1.13%. As a result of this study, it was confirmed that the laser tabbing system developed in this research can be applied in module manufacturing processes.

Long Afterglow SrAl2O4:Eu2+,Dy3+ Phosphors as Luminescent Down‐Shifting Layer for Crystalline Silicon Solar Cells

SrAl2O4:Eu2+,Dy3+ phosphors can convert near ultraviolet light with lower sensitivity to the solar cell to yellow‐green light at which the solar cell has higher sensitivity and exhibit the excellent luminescent property of long persistence. Therefore, in this study, the authors firstly synthesized the fine SrAl2O4:Eu2+,Dy3+ phosphors and then produced SrAl2O4:Eu2+,Dy3+/SiO2 composite films as spectral shifters to understand the effects of SrAl2O4:Eu2+,Dy3+ phosphor on photoelectric conversion efficiencies of a crystalline silicon photovoltaic module. Under one sun illumination, the composite film containing an appropriate amount of SrAl2O4:Eu2+,Dy3+ phosphor enhances the photoelectric conversion efficiency of the cell through spectral down‐shifting as compared to the bare glass substrate, and the maximum achieves 11.12%. In contrast, the commercial SrAl2O4:Eu2+,Dy3+ phosphor composite film is not effective for improving the photoelectric conversion efficiency because of the relatively lower visible light transmittance of film caused by the large aggregates. After one sun illumination for 1 min, the light source was turned off, and the cell containing the synthesized SrAl2O4:Eu2+,Dy3+ phosphor still shows an efficiency of 1.16% in the dark due to the irradiation by the long persistent light from SrAl2O4:Eu2+,Dy3+, which provides a possibility to fulfill the operation of solar cells even in the dark.

결정계 PV 모듈에 대한 고장 메커니즘 검토

It is summarized that potential causes of performance degradations and failure mechanisms of crystalline silicon photovoltaic (PV) modules installed in Middle East area. In addition, we also reviewed current PV module qualification test (IEC 61215) and the methods for detection of wear-out fault. The failure of PV modules in the extreme environmental conditions such as deserts is mainly due to high temperature, humidity, and dust storms. In particular, cementation phenomenon caused by combination of sand and moisture leads to rapid degradation in the performance of PV modules. In order to evaluate and guarantee the long term reliability of PV modules, specific qualification tests such as sand dust test, salt mist test and potential induce degradation test considering operating environment of PV module should be carried out.

Degradation evaluation of crystalline-silicon photovoltaic modules after a few operation years in a tropical environment

This paper presents an evaluation of the performance degradation of Photovoltaic modules after few operation years in a tropical environment. To this end, the International Center for Research and Training in solar energy at Dakar University and the Lasquo-ISTIA laboratory of Angers University have put in place a research project in order to investigate the impact of the tropical climatic conditions on the PV modules characteristics. Accordingly, two monocrystalline-silicon (mc-Si) PV modules and two polycrystalline- silicon (pc-Si) PV modules are installed at Dakar in Senegal and monitored during a few operation years: Module A (16 months), Module B (41 months), Module C (48 months) and Module D (48 months). After few operation years under tropical environment, the global degradation and the degradation rate of electrical characteristics such as I-V and P-V curves, open-circuit voltage (Voc), short-circuit current (Isc), maximum ouput current (Imax), maximum output voltage (Vmax), maximum power output (Pmax) and fill factor (FF) are evaluate at standard test conditions (STC). This study reports on data collected from 4 distinct mono- and poly-crystalline modules deployed at Dakar University in Senegal. The study has shown that Pmax, Imax, Isc and FF are the most degraded performance characteristics for all PV modules. The maximum power output (Pmax) presents the highest loss that can be from 0.22%/year to 2.96%/year. However, the open-circuit voltage (Voc) is not degraded after these few exposition years for all studied PV modules.

Water Cooling Method to Improve the Performance of Field-Mounted, Insulated, and Concentrating Photovoltaic Modules

The installation rate of crystalline silicon photovoltaic (PV) modules worldwide is at an all-time high and is projected to continue to grow as the cost of PV technology is reduced. It is important to note that PV power generation is heavily influenced by the local climate. In particular, for crystalline silicon-based PV devices, as the operating temperature of the panel increases, the efficiency decreases. Higher operating temperatures also lead to accelerated material and mechanical degradation, potentially compromising system effectiveness over the lifetime of the panels. In addition, atmospheric pollution can cause particle deposition on the surface of PV modules (soiling), reducing the amount of solar irradiance that reaches the PV material and reducing panel efficiency. Various cooling and cleaning methods have been proposed in the literature to mitigate these problems. In this study, a uniform film of water was continuously recirculated by pumping over the surface of a solar panel using an emitter head attached to the top of the panel. The water cooling technique was able to maintain panel temperature below 40 °C while adjacent untreated panels were operating near 55 °C. Besides the efficiency improvements due to cooling, the film of water also kept the panels clean, avoiding any reduced power output caused by panel soiling. Additional studies were carried out with artificially chilled cooling fluid, insulating materials, and side mirrors to examine the cooling system performance under different installation scenarios. Water cooling is concluded to be an effective means of increasing the efficiency of monocrystalline silicon photovoltaic panels. Under normal operating conditions, the increased energy output from the panels is more than sufficient to compensate for the energy required to pump the water.

Prediction of silicon PV module temperature for hot spots and worst case partial shading situations using spatially resolved lock-in thermography

In this paper we propose a method to predict hot spot temperatures in crystalline silicon photovoltaic modules operating under critical shading conditions prior to module fabrication. We developed a unique tool to evaluate the damage risk potential for an individual solar cell. We show that shading conditions leading to the most critical hot spot temperature do not necessarily coincide with the shading conditions for the maximum total power dissipation in the shaded cell. In fact, for an adequate prediction of temperature fields and the worst case shading scenario, spatially resolved information of the power dissipation on cell level and a thermal simulation of the module system are indispensable. Our approach is divided into three steps, starting with an electric network simulation of cell operating points for different shading scenarios. For these operating points we perform spatially resolved lock-in thermography measurements of the power dissipation on cell level. On that basis we compute three-dimensional temperature fields inside the module with a finite-element analysis for different realistic module operating conditions. The model is validated with experimental data on a module of industrial cells.

Effect of moisture condensation on long-term reliability of crystalline silicon photovoltaic modules

Moisture condensation (MC) can occur in photovoltaic (PV) modules in hot and humid climates, and the resulting water droplets can cause more areas of corrosion. Therefore, in this study, MC history of PV modules exposed to Miami climate (FL, USA) has been derived employing corresponding meteorological data. The duration of MC versus temperature of PV module (Tmodule) was calculated over 1year. Furthermore, five types of accelerated tests were conducted to develop a MC-induced degradation prediction model. The thermal activation energy, 0.4524eV, was calculated. The Brunauer–Emmett–Teller (BET) model was used to predict the degradation rate. The accumulated degradation rate of a PV module exposed to the accelerated condition of MC was 1.45times greater than that of damp heat (DH). The effect of encapsulant materials on the frequency of MC and accumulated degradation rate over 1year were calculated in the Miami climate.

The energy payback time of advanced crystalline silicon PV modules in 2020: a prospective study

ABSTRACTThe photovoltaic (PV) market is experiencing vigorous growth, whereas prices are dropping rapidly. This growth has in large part been possible through public support, deserved for its promise to produce electricity at a low cost to the environment. It is therefore important to monitor and minimize environmental impacts associated with PV technologies. In this work, we forecast the environmental performance of crystalline silicon technologies in 2020, the year in which electricity from PV is anticipated to be competitive with wholesale electricity costs all across Europe. Our forecasts are based on technological scenario development and a prospective life cycle assessment with a thorough uncertainty and sensitivity analysis. We estimate that the energy payback time at an in‐plane irradiation of 1700 kWh/(m2 year) of crystalline silicon modules can be reduced to below 0.5 years by 2020, which is less than half of the current energy payback time. Copyright © 2013 John Wiley & Sons, Ltd.

Predicted Thermal Stresses in a Trimaterial Assembly With Application to Silicon-Based Photovoltaic Module

Low-temperature thermally induced stresses in a trimaterial assembly subjected to the change in temperature are predicted based on an approximate structural analysis (strength-of-materials) analytical (“mathematical”) model. The addressed stresses include normal stresses acting in the cross-sections of the assembly components and determining their short- and long-term reliability, as well as the interfacial shearing and peeling stresses responsible for the adhesive and cohesive strength of the assembly. The model is applied to a preframed crystalline silicon photovoltaic module (PVM) assembly. It is concluded that the interfacial thermal stresses, and especially the peeling stresses, can be rather high, so that the structural integrity of the module could be compromised, unless appropriate design for reliability measures are taken. The developed model can be helpful in the stress analysis and physical (structural) design of the PVM and other trimaterial assemblies.

High Voltage Stress Impact on P Type Crystalline Silicon PV Module

The effects of the high voltage stress and other environmental conditions on crystalline silicon photovoltaic module performance have not been included in the IEC 61215 or other qualification standards. In this work, we are to evaluate the potential induced degradation on p type crystalline silicon PV modules by three cases, one case is in room temperature, 100% relative humidity water bath, another is in room temperature, the front sheet coverage with aluminum foil and the other is in the 85°C, 85% relative humidity climate chamber. All the samples are applied with the -1000 V bias to active layers, respectively. Our current-voltage measurements and electroluminescence results showed in these modules power loss of 37.74%, 11.29% and 49.62%, respectively. These test results have shown that among high voltage effects the climate chamber is the harshest and fastest test. In this article we also showed that the ethylene vinyl acetate volume resistivity and soda-lime glass ingredients are important factors to PID failure. The high volume resistivity which is more than 1014 Ω·cm and Na less contents glass will mitigate the PID effect to ensure PID free.

Testing and Analysis for Lifetime Prediction of Crystalline Silicon PV Modules Undergoing Degradation by System Voltage Stress

Acceleration factors are calculated for crystalline silicon photovoltaic modules under system voltage stress by comparing the module power during degradation outdoors with that in accelerated testing at three temperatures and 85% relative humidity. A lognormal analysis is applied to the accelerated lifetime test data, considering failure at 80% of the initial module power. Activation energy of 0.73 eV for the rate of failure is determined for the chamber testing at constant relative humidity, and the probability of module failure at an arbitrary temperature is predicted. To obtain statistical data for multiple modules over the course of degradation in situ of the test chamber, dark I–V measurements are obtained and transformed using superposition, which is found to be well suited for rapid and quantitative evaluation of potential-induced degradation. It is determined that shunt resistance measurements alone do not represent the extent of power degradation. This is explained with a two-diode model analysis that shows an increasing second diode recombination current and ideality factor as the degradation in module power progresses. Failure modes of the modules stressed outdoors are examined and compared with those stressed in accelerated tests.

Lifetime Estimation of a Photovoltaic Module Subjected to Corrosion Due to Damp Heat Testing

In this paper, a methodology is presented for estimating the lifetime of a photovoltaic (PV) module. Designers guarantee an acceptable level of power (80% of the initial power) up to 25 yr for solar panels without having sufficient feedback to validate this lifetime. Accelerated life testing (ALT) can be carried out in order to determine the lifetime of the equipment. Severe conditions are used to accelerate the ageing of components and the reliability is then deduced in normal conditions, which are considered to be stochastic rather than constant. Environmental conditions at normal operations are simulated using IEC 61725 standard and meteorological data. The mean lifetime of a crystalline-silicon photovoltaic module that meets the minimum power requirement is estimated. The main results show the influence of lifetime distribution and Peck model parameters on the estimation of the lifetime of a photovoltaic module.

Performance analysis of a multi crystalline Si photovoltaic module under Mugla climatic conditions in Turkey

Commercially available, a multi crystalline silicon (mc-Si) photovoltaic (PV) module has been monitored outdoors under Mugla climatic conditions in Turkey. Electricity yield of this module is calculated from the uninterruptible measured current–voltage curves from sunrise to sunset during a year. Calculated electricity yield from the measured plane of array or in-plane (POA) irradiation is compared with the calculated electricity from the manufacturer’s electrical values of the module and the measured electricity from the photovoltaic system consisting 26 mc-Si PV modules from the same manufacturer. Calculated annual energy rating for the PV system is 1415.79kWh/kWp and 1414.18kWh/kWp from the manufacturer data and tested module respectively. The measured energy rating value is 1412.78kWh/kWp. Comparison of results from this study with those obtained from the measurements show that the average difference in monthly electricity values varies between ±12% with an annual average value less than 1% and a performance ratio (PR) of 0.72.

Early Failure Detection of Interconnection with Rapid Thermal Cycling in Photovoltaic Modules

To accelerate the degradation with thermal fatigue in crystalline silicon photovoltaic modules, the modules were exposed to dry thermal stress with rapid thermal cycling, and module impedance was monitored in situ during this testing. The spikelike increase in module impedance at a temperature-alteration point was observed in the early stage of this rapid thermal cycling. The pattern of increase in module impedance proceeded step-by-step, from the early stage, via the double-spikelike pattern at two temperature-alteration points (the middle stage), and finally to the successive increases in module impedance in the high-temperature period (the late stage). The nondestructive analyses suggest that the interconnector failures without the defects of photovoltaic cells occurred. From these results, it is suggested that the pattern of increase in module impedance is related to the interconnection degradation of modules, and that the rapid thermal cycling with in situ monitoring of module impedance would be a useful procedure for the earlier detection of interconnection failures in photovoltaic modules.

Epidemiological Analysis of Degradation in Silicon Photovoltaic Modules

We have studied the power reduction rate and degradation modes of crystalline-silicon photovoltaic modules, which had been operated in an outdoor field for about 10 years. We measured the electric parameters of the modules before and after 10-year operation, and classified our photovoltaic modules into four groups that were manufactured by four manufacturers. Analyzing the age-related decreases in electric parameters of the modules, we found two dominant degradation modes by correlation analysis of the electric parameters. In addition, we found delamination mode degradation by visual inspection. We have recognized a degradation rate in terms of the statistical distribution of the module power reduction. The power reduction rate was found to be an average of 4.7% for ten years.

A procedure to calculate the five-parameter model of crystalline silicon photovoltaic modules on the basis of the tabular performance data

Only few manufactures provide the wide set of graphical data that are necessary to use high performance predictive tools for PV systems. On the other hand, reliable graphical data require accurate laboratory measurements that increase manufacturing costs. For this reason PV system designers have to choose between the use of cheap PV modules, lacking in technical data, and the reliable energy predictions that are possible only if the current–voltage characteristics are provided by the PV module manufacturers.This paper describes the procedure to evaluate the parameters of a one-diode equivalent circuit able to accurately represent the electrical behaviour of a PV panel by means of the minimum set of technical data that are usually provided by all manufacturers. To reach the purpose some correlations based on the survey of more than one hundred PV module characteristics were defined to make up for the lack of technical information. The computer routines used to evaluate the values of the model parameters are listed; the routines are written in BASIC and can be easily implemented, even like VBA macros in Microsoft Excel.The capability of the new model to calculate the current–voltage characteristics was tested by comparing the results with data measured by four different manufacturers. The results of the application of the new model confirm the reliability of the proposed procedure. The differences between the calculated and the measured data are always less than the data tolerance usually declared by the manufacturers.