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Solar cell modules are connected in series and parallel in a photovoltaic system. All the solar cell modules degrade over time and the most degraded module in a string decides the output level of the string. In this study, we suggest a health monitoring method which enables to detect the most degraded module in a string without separating the module from the string. The method places a non-transparent film on a module in a string to make an artificial shading effect and monitors the current-voltage curve of the string while placing the film to the next one. We show analytically that the most degraded module can be detected by comparing all the string current-voltage curves. We demonstrate the method on an outdoor photovoltaic string.

The lifetime of solar cell modules is an important factor in the reduction of solar energy costs. To enhance the lifetime of silicon solar cell module under thermal cycling, numerical analysis and optimization are conducted on a conventionally designed solar cell module. A series of sensitivity studies with a numerical model reveals the thicknesses of Cu and Si should be reduced to enhance the lifetime under thermal cycling. The lifetime of the reliability-enhanced design is expected to increase by 159% compared to that of the conventional module.

Dye-sensitized solar cell (DSC) is a promising candidate for the application in building-integrated photovoltaics (BIPV). At higher temperature above 85 °C, the reliability of the module has remained a major challenge yet. A large DSC module, sized 300 × 300 mm 2 , is developed. In the preliminary module design, the width of cell is 11 mm and the coefficients of temperature expansion (CTE) for sealant and electrolyte are 699 and 807 ppm/°C, respectively. The modules are stored in 85 °C. The power conversion efficiency of the modules drops rapidly in 100 h during the test. To analyze and enhance the module design in view of reliability, finite element model is developed for the module. Stress analysis reveals that high stresses in electrode cause the breakage of electrode and sealant in succession and the loss of electrolyte finally. From a parameter sensitivity analysis with the finite element model, it is identified that the maximum stress in electrode can decrease when the cell width increases. CTEs of sealant and electrolyte can be also optimized as analysis confirms that the maximum stress in electrode drops when the CTEs of sealant and electrolyte decrease. Based on the studies, new module design is formulated, which have the cell width of 18 mm and the CTEs of 277 and 656 ppm/°C for sealant and electrolyte, respectively. The new modules are tested in 85 °C and show much better lifetime than the preliminary one without the leakage of electrolyte.

A Glass-to-Glass (G2G) CuInxGa1-xSe2 (CIGS) solar cell module is a promising thin-film solar technology; however, it is highly sensitive to moisture-induced degradation. Many studies have been conducted on the lifetime prediction model of this technology. However, none of these studies considered the spatial effects of moisture propagation on degradation. This study introduced a novel method, the spatially distributed diode model (SDDM), and predicted the lifetime of G2G CIGS solar modules for moisture-induced degradation. We analyzed the diffusion of spatial moisture concentration on the CIGS solar modules and estimated the model parameters using degradation data. The proposed method can predict the lifetime of any size or shape of G2G CIGS module for moisture-induced degradation. Furthermore, the method can be used to envision a possible longer lifetime for the solar modules depending on the selection of physical appearance of the modules and installation location.

Recently, life prediction models for Pb-based and Pb-free solders used in chip resistor assemblies under thermal cycling have been introduced. The models suggest that the field lifetimes of Pb-free solders would be better than those of Pb-based solders when used for chip resistors under thermal cycling conditions, while the lifetime of the chip assemblies under accelerated test conditions show a reverse relationship. In this study, the prediction models were verified by applying the model to another research case. Finite element models were built, thermal cycling conditions were applied, and the energy densities were calculated. Finally, life prediction analysis was conducted for the cases where Pb-based and Pb-free solders were used. The prediction results were then compared with the test data of the case. It was verified that the predictions of the developed life cycle models are on the practical scale. † Corresponding Author, cw_han@keti.re.kr Ⓒ2016 The Korean Society of Mechanical Engineers

To enhance the reliability of the thin-film solar cell technologies, it is required to analyze and understand the moisture-induced degradation. In this study, the moisture induced degradation of glass-to-glass CIGS module are comprehensively analyzed. CIGS modules are fabricated and tested under damp-heat conditions with periodical measurement of the electrical characteristics. Individual layers of the module are also investigated experimentally and the moisture induced degradation is discussed. A modified method to extract the diode model parameters from degraded I–V curves is proposed and applied to the degraded data. Finally, the degradation rates are modelled and the effect of model parameters degradation on the power of module are quantitatively compared. It suggests that the power degradation of CIGS module under the damp-heat environment is more affected by the enhanced recombination of the absorber layer than the degradation of the metal layer or the leakage over layers.

A thermal cycling test was conducted on a chip resistor solder joint with real-time failure monitoring. In order to study the failure mechanism of the chip resistor solder joint during the test, the resistance between both ends of the resistor was monitored until the occurrence of failure. It was observed that the monitored resistance first fluctuated linearly according to the temperature change. The initial variation in the resistance occurred at the time during the cycle when there was a decrease in temperature. A more significant change in the resistance followed after a certain number of cycles, during the time when there was an increase in the temperature. In order to explain the failure patterns of the solder joint, a mechanism for the solder failure was suggested, and its validity was proved through FE simulations. Based on the explained failure mechanism, it was shown that prognostics for the solder failure can be implemented by monitoring the resistance change in a thermal cycle condition.

Large-scaled dye-sensitized solar cell (DSC) modules are recently developed for building-integrated photovoltaic (BIPV) applications. In the modules, two glasses with electrodes and dye are sealed together to prevent the leakage of liquid electrolyte. It is known that DSC modules deteriorate rapidly under high temperature conditions. Previous studies showed that expansion of liquid electrolyte in the module is the main reason for the degradation; the expansion of electrolyte induces the breakage of sealant material of DSC module in high temperature. This study investigates how the sealant curing process affects the integrity of DSC module in high temperature. Sealant samples are made up by several UV curing times. Shadow moire technique is used to measure the coefficient of thermal expansion (CTE) of the sealant samples. With the test results, finite element analyses are conducted to optimize the curing process time. It is finally suggested that the longer the curing time, the more robust the DSC module.

Large-scaled Dye-sensitized solar cell (DSC) modules are recently developed for BIPV applications. In the modules, two glasses with electrodes and dye are joined for electrolyte and sealed together to prevent the leakage of electrolyte. Test of the module in a high temperature environment discloses several symptoms of electrolyte leakage through sealing failure. A finite element model is developed for the DSC module to investigate the sealing failure from the different thermal expansions. The accuracy of the model is validated by experimenting the deformation patterns of the module in high temperature and comparing with the model results. Finally, the sensitivities of the cell width and glass thickness are studied and optimal configuration is suggested for preventing the sealing failure of DSC.

This paper focuses on the effect of delamination on electrical performance in PV module, especially electrical loss of solar cell. Degradation mode of field aged crystalline-Si PV module has been investigated through visual microscope. Electrical performance was measured with solar simulator. Electroluminescence analysis was carried out for detecting defects of PV module. Delamination observed in the PV module has occurred at the interface between the encapsulant and the front surface of the solar cell and between the encapsulant and glass. Delamination was a main degradation mode of PV module. To describe the effect of delamination on the electrical performance, new analysis through line irradiance system for electrical mapping was used. Investigation of delamination indicated that new analysis is useful to describe the effect of delamination compared to the electroluminescence analysis.

An accelerated thermal cycling test to assess the reliability of lead-free solders at chip resistor has been conducted. Test results indicate that the life of lead-free solder at chip resistor (6432 mm type) could be worse than of SnPb solder in the accelerated thermal cycling condition (125/-50C). Based on the test results and some published data, life prediction model for the solders has been developed. The developed life prediction model consists of stress model and damage model. Stress model, which relates thermal cycling condition to damage at solder, includes FE model with Anand's constitutive equation for solders. Damage model, which relates the damage to life of solder, is based on Darveaux' crack growth approach. Developed life prediction model confirms worse reliability of lead-free solder than leaded solder in the accelerated thermal cycling condition but potentially predicts reverse results in the field condition. To predict the reliability of lead-free solder in the field condition, accelerated factor should be carefully calculated using life prediction model.

Phase-shifting in an achromatic configuration of moiré interferometry is explained. The rigorous diffraction theory defines the phase of diffracted beams in terms of the pitch and the relative position of a compensator grating. A numerical analysis proceeds to determine the total phase change between two diffracted beams that produce moiré fringes.