Photovoltaic Cell Module Research Articles

Modelling the non-isothermal curing kinetics of peroxide crosslinking polyolefin copolymers for photovoltaic module lamination

This study presents a model for determining the non-isothermal curing kinetics of peroxide crosslinking polyolefin copolymers used for encapsulation of silicon solar cells in photovoltaic modules. Therefore, rheological data of ethylene vinyl acetate copolymer (EVA) and polyolefin elastomer (POE) were analyzed. The curing kinetics were described assuming a temperature dependent Arrhenius rate coefficient and implementing a reaction rate model. Validation was performed under isothermal and non-isothermal conditions. An excellent agreement of experimental and model data was ascertained. The model was used to determine the non-isothermal crosslinking conversion during lamination of EVA or POE based photovoltaic mini-modules. Temperatures were tracked by positioning seven sensors within the mini-modules. Moreover, a thermal simulation model was implemented. Also on module level, the experimental results corroborated the simulated data. A lamination temperature of 150 °C led to insufficient curing of POE based modules. Similar conversion rates were achieved for EVA and POE encapsulants at 150 and 160 °C, respectively.

Development and performance assessment of a hybrid solar cabinet dryer for fish drying

The fish products can be stored for longer period in dry condition, but most of the fresh fish in remote areas of our country are spoils due to lack of proper preservation. To overcome this problem, hybrid solar dryer can play an important role to make drying continuous during night and daytime also off sunshine hours. In this project, a hybrid solar cabinet dryer has been designed, constructed, and performance tested for fish drying. The dryer consists of a drying chamber, solar collector, two trays of dimensions (60×60) cm and paraffin wax as PCM. It also consists of photovoltaic cell modules, heating element, electric battery, and other electric equipment such as inlet and outlet fans. The dryer has been operated as both a solar energy dryer during normal sunny days and a hybrid solar dryer during cloudy days. Paraffin wax system inside drying chamber absorbed heat energy in Sunny time. At the same time the battery is charged from the solar system and therefore the water kept in the tank reaches a certain temperature by absorbing heat from nature, which provides heat by circulating the water inside the drying chamber during inclement weather. Electric fans are used at the inlet of the solar collector and outlet of the dryer to maintain adequate air flow inside the drying chamber. During the night and cloudy weather paraffin wax and heater system deliver heat to maintain the set temperature in drying chamber. The grain bed in the dryer is heated by air that comes from a separate solar collector, and at the same time, the drying cabinet collects solar energy directly through the transparent walls and roof. The dryer demonstrated the capacity to dry fish to an appropriate moisture level in a reasonable amount of time, and concurrently, it insured that the fish would be of high quality. The drying rate of hybrid solar dryers is evaluated on fresh fish and compared with solar dryers and sun drying under the same climatic conditions.

Solar concentrators filled with liquid for enhancement of photocurrent generation and angular responses of light incidence

Design and manufacturing of solar concentrator materials and structures for external light trapping have been widely explored for decades to enhance solar cell performances in various photovoltaic (PV) devices such as silicon, organic, and perovskite ones. Among them, remarkable progress in development of the concentrators has been made to improve the solar concentration ratio of power conversion efficiency (PCE). However, only some studies were carried out to enhance the angular responses of light incidence (AOI). This paper reports a simple liquid-filled solar concentrator (LFSC) that can be effectively implemented by incorporating optical reflection with total internal refraction (TIR). Using the fused deposition modeling (FDM) method in the 3D printing process, the hollow compound concentrators in a parabolic shape were efficiently produced at a low cost. With liquid water and silicone oil, the simulation and experimental results illustrated that the PCE and AOI were increased for the concentrator solar cells composed of bulk heterojunction structure. In particular, it was found that all the AOI exhibited an exponential decay as a Gaussian distribution. Hence, it provided the capability of control over concentrator material and geometry in design and fabrication. In this manner, various such simple devices fabricated by the present method can be further applied in future applications such as PV cell modules and systems.

Surface Reconstruction of Lead-Free Perovskite Cs2Ag0.6Na0.4InCl6:Bi by Hydroxylation with Blue-Light-Excited Performance

Molecular surface reconfiguration strategies have been instrumental to performance improvements of halide perovskite photovoltaic applications in recent years. However, research into the optical properties of the lead-free double perovskite Cs2AgInCl6 on the complex reconstructed surface is still lacking. Here, blue-light excitation in double perovskite Cs2Na0.4Ag0.6InCl6 with Bi doping has been successfully achieved by excess KBr coating and ethanol-driven structural reconstruction. Ethanol drives the formation of hydroxylated Cs2-yKyAg0.6Na0.4In0.8Bi0.2Cl6-yBry in the Cs2Ag0.6Na0.4In0.8Bi0.2Cl6@xKBr interface layer. The hydroxyl group adsorbed on the interstitial sites of the double perovskite structure induces a transfer of local space electrons to the [AgCl6] and [InCl6] octahedral regions, enabling them to be excited with blue light (467 nm). The passivation of KBr shell reduces the non-radiative transition probability of excitons. Blue-light-excited flexible photoluminescence devices based on hydroxylated Cs2Ag0.6Na0.4In0.8Bi0.2Cl6@16KBr are fabricated. The application of hydroxylated Cs2Ag0.6Na0.4In0.8Bi0.2Cl6@16KBr as down-shift layer in GaAs photovoltaic cell module can increase its power conversion efficiency by 3.34%. The surface reconstruction strategy provides a new way to optimize the performance of lead-free double perovskite.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Mechanistic Understanding of Polarization‐Type Potential‐Induced Degradation in Crystalline‐Silicon Photovoltaic Cell Modules

Potential‐induced degradation (PID) has been identified as a central reliability issue of photovoltaic (PV) cell modules. Several types of PID depend on the cell structure. Among those types, polarization‐type PID, which is characterized by reductions in short‐circuit current density (JSC) and open‐circuit voltage (VOC), is the fastest PID mode. Additionally, polarization‐type PID occurs readily at room temperature or at markedly low magnitudes of electric potential difference. Therefore, polarization‐type PID is a severe difficulty affecting silicon PV modules. Recently, degradation behavior, preventive measures, and mechanism have been investigated. As described herein, mechanistic aspects of polarization‐type PID are specifically examined and details of a recently proposed model involving a charge accumulation process at K centers in SiNx dielectric layers: the K‐center model are discussed. The K‐center model consistently explains previously reported results of experimentation, which indicates the validity of this model. Discussions presented herein are expected to improve the mechanistic understanding of polarization‐type PID in the PV community and to stimulate further discussions and verifications of the model.

Review of technology specific degradation in crystalline silicon, cadmium telluride, copper indium gallium selenide, dye sensitised, organic and perovskite solar cells in photovoltaic modules: Understanding how reliability improvements in mature technologies can enhance emerging technologies

AbstractA comprehensive understanding of failure modes of solar photovoltaic (PV) modules is key to extending their operational lifetime in the field. In this review, first, specific failure modes associated with mature PV technologies, such as crystalline silicon (c‐Si), copper indium gallium selenide (CIGS) and cadmium telluride (CdTe), are framed by sources of specific failure modes, their development from the early‐developmental stages onwards and their impact upon long term performance of PV modules. These failure modes are sorted by both PV technology and location of occurrence in PV modules, such as substrate, encapsulant, front and rear electrode, absorber and interlayers. The second part of the review is focused on emerging PV technologies, such as perovskites solar cells, dye sensitised and organic PVs, where due to their low to medium technology readiness levels, specific long‐term degradation mechanisms have not fully emerged, and most mechanisms are only partially understood. However, an in‐depth summary of the known stability challenges associated with each emerging PV technology is presented. Finally, in this paper, lessons learned from mature PV technologies are reviewed, and considerations are given in to how these might be applied to the further development of emerging technologies. Namely, any emerging PV technology must eventually pass industry‐standard qualification tests, while warranties for the lifetime of modern c‐Si‐based modules might be extended beyond the existing warranted life of 25 years.

Modeling and Performance Analysis of Simplified Two-Diode Model of Photovoltaic Cells

For a quick and consistent photovoltaic (PV) module design, an effective, fast, and exact simulator is crucial to examine the performance of the photovoltaic cell under partial or quick variation of temperature and irradiance. The most prevalent modeling strategy is to apply an equivalent (electrical) circuit that encompasses together non-linear and linear mechanisms. This work proposes the modeling and analysis for a four-parameter two-diode photovoltaic cell model based on the manufacturer's data-sheet. The proposed model needs only four parameters compared to the previously developed seven-parameter two-diode model to reduce the computational complexity. To develop a specific model of photovoltaic cells, the fundamental requirement is the data of temperature and irradiance. The variation of these variables totally affects the output constraints like current, voltage, and power. Thus, it is substantial to design a precise model of the photovoltaic cell module with a reduced computation period. The two-diode photovoltaic module with four constraints is identified to be more accurate and have improved performance compared to a one-diode model particularly at lower irradiance. To confirm the accuracy of the proposed model the method is applied on two different photovoltaic modules. The proposed model and modeling method are helpful for power electronic designers who require a fast, accurate, simple, and easy to implement method for use in photovoltaic system simulation. The electrical equivalent circuit and standard equations of photovoltaic cells are analyzed and the proposed two-diode model is simulated using MATLAB/Simulink software and validated for poly-crystalline and mono-crystalline solar cells under standard test conditions.

Design and research of photovoltaic modules in energy routers based on cascaded H-bridge

Aiming at the shortcomings of traditional photovoltaic modules in energy routers, a new structure of cascaded H-bridge photovoltaic module is designed in this paper, including photovoltaic cell module, Boost/Buck module with inertial energy links, and chain H-bridge module. The maximum power point tracking (MPPT) control algorithm and the chain cascaded H-bridge control algorithm are studied, and the control angle table of the full chain 12H-bridge and the missing chain 11H-bridge is given. A 12H-bridge cascade model is built in the EMTP simulation software to verify the feasibility of the H bridge cascade output and it proves that its harmonic content is small and the power quality is high. Finally, a chain cascaded photovoltaic panel is produced, showing that it can output AC power smoothly. Comparing the daily power generation of the new photovoltaic module and the traditional photovoltaic module, it proves that it has more power generation and better irradiance tracking performance.

Experimental thermodynamic performance analysis of semi-transparent photovoltaic-thermal hybrid collectors using nanofluids

In this article, the experimental thermodynamic performance analysis of a semi-transparent photovoltaic-thermal hybrid collector (SPV-THC) using CuO, Al2O3, TiO2 based nanofluids and water is investigated and compared with conventional opaque photovoltaic panels. The SPV-THC consists of a polycrystalline silicon cell photovoltaic module with a serpentine tube configuration heat sink. The influence of nanoparticle concentration, mass flow rate of nanofluids, ambient factors such as solar irradiation and ambient temperature on thermodynamic performance of SPV-THC have been experimentally studied under the weather conditions in Coimbatore, India. The concentration of nanoparticles and mass flow rate of nanofluids were optimized to 0.2% (by volume) and 0.016 kg/s, respectively based on experimental trials. The experimental result shows that the electrical efficiency of SPV-THC using CuO, TiO2, Al2O3 based nanofluids and water has been improved by 11.2%, 9.1%, 7.3% and 5.9% respectively than the conventional opaque photovoltaic modules. Also, the thermal efficiencies of SPV-THC using CuO, TiO2 and Al2O3 nanofluids improved by 42.6%, 34.8% and 19.7% respectively than water.

Multiscale Modeling of Shingled Cell Photovoltaic Modules for Reliability Assessment of Electrically Conductive Adhesive Cell Interconnects

New interconnect schemes that replace metallic solders with electrically conductive adhesives (ECA) are appearing in recent embodiments of crystalline silicon photovoltaic (PV) modules. Recently, potential ECA interconnect failure modes were identified and characterized, which included cohesive cracking and debonding of the adhesive joint. In this work, we elucidate on how and to what extent the driving force for ECA degradation develops in shingled cell modules. We have employed a multiscale modeling approach, using the finite-element method, to accurately predict the driving force for both accelerated stress testing conditions and on-sun exposure of PV modules. When we compare our driving force predictions for a generic PV module with the experimentally characterized fracture properties of a candidate ECA, we found that interconnect failure of only poor quality or otherwise damaged joints is likely to occur. Furthermore, we show how a 2-D submodel can efficiently predict limits for the debond driving forces without needing to employ the multiscale modeling approach.

Close examination of localized hot spots within photovoltaic modules

For photovoltaic modules, hot-spot phenomena are very common and influential, affecting device performance and causing irreversible damage. Researchers mainly pay attentions to hot-spot phenomena from a large-scale view that hot spots result from module failures, i.e., abnormal solar cells in photovoltaic modules are heated by other normal cells as loads. However, this heating process may not be the start of hot-spot phenomena. The large-scale hot-spot phenomena may develop from localized temperatures anomaly within a unit cell in the module while current researches generally ignored this small-scale but important problem. In this paper, close inspection of localized hot spots within photovoltaic modules is conducted with a xenon lamp of simulating the solar irradiation. An electronic load and an infrared thermal camera are utilized to detect and analyze electrical and thermal characteristics of the tested cells under different irradiation and surface conditions. With this experimental system, the localized hot-spot phenomena within a unit cell are experimentally revealed and the transient forming and variation processes of hot spots resulted from different mechanisms are explored, which are seldom reported to our knowledge. Attributed to localized hot spots, power conversion efficiency may fall to as low as 1.58% from 15.61%. In addition to the non-uniform irradiation, environmental obstructions falling on the cell surface may also form hot spots of very high temperature. Dust covering on the cell may lead to a hot spot above 64 °C, reducing cell efficiency by as much as 5.7 percent. The easily ignored localized hot-spot phenomena must be handled properly in case they get exacerbated and expand to the whole module.

Power quality issue simulation in solar energy

Power quality issue simulation in solar energy presents simulink of sag issue generated usually in PV panels. This simulation is aimed at supplying electrical energy using solar power at remote ends, domestic and Industrial Applications. Solar radiation energy accounts for most of the usable renewable energy on Earth. Solar energy is the alternative for conventional source of energy. The need to generate pollution free energy has triggered the effective usage of solar energy interconnection with the grid. Photovoltaic (PV) method of generating electrical power by converting solar radiation into direct electrical current uses semiconductor that exhibits the photovoltaic effect. This work focuses on a program development in MATLAB/Simulink of 47 cell photovoltaic module PV array.

Influence of emitter position of silicon heterojunction photovoltaic solar cell modules on their potential-induced degradation behaviors

Potential-induced degradation (PID)-test results of modules fabricated from the rear- and front-emitter silicon heterojunction (SHJ) solar cells were compared to clarify the influence of the emitter position of SHJ photovoltaic (PV) cell modules on their PID behaviors. The PID tests were performed by applying a bias of −2000 V to the shorted interconnector ribbons from the front surface of the cover glass, at 85 °C. In the initial stage, both modules showed the same degradation characterized by a reduction in the short-circuit current density (Jsc). After the first-stage degradation, the rear-emitter SHJ PV modules exhibited subsequent degradation characterized by a significant reduction in the Jsc and open-circuit voltage (Voc), due to the enhancement of the minority-carrier recombination in the front surface region of the n-type crystalline silicon base. The front-emitter SHJ PV modules, on the other hand, showed a reduction in the fill factor (FF), in addition to moderate reductions in Jsc and Voc. The FF reduction of the front-emitter SHJ PV modules is considered to be caused by the enhancement of the recombination in the front surface region of the n-type crystalline-silicon base as the region corresponds to the pn junction interface of the front-emitter configuration. The moderate reductions in both Jsc and Voc may be due to further progression of the first-stage degradation. These findings are essential for understanding the mechanism of PID in SHJ PV cell modules.

Small scale optimization in crystalline silicon solar cell on efficiency enhancement of low-concentrating photovoltaic cell

Compared with conventional silicon solar cell, concentrating photovoltaic cell has a higher incident illumination intensity and non-uniform illumination intensity distribution. There is a close relationship between the illumination intensity and the resistance and shading losses of front metal fingers. In this paper, according to the non-uniformity of the illumination distribution formed by the concentrator, the effects of different finger numbers and spacing on the performance of low-concentrating photovoltaic cells were studied. First, low-concentrating photovoltaic cell modules with different finger numbers and spacing were established, and efficiency of these modules was compared to determine the optimal finger numbers and spacing of the front metal fingers. Then, effects of the shading losses, finger resistance and lateral spreading resistance on the performance of the low-concentrating photovoltaic cell were analyzed. Results show that for the specific illumination intensity distribution of the low-concentrating photovoltaic cell when the numbers and spacing of the front metal fingers are optimized, efficiency of the low-concentrating photovoltaic cell can be increased from 13.805% to 13.837%. Additionally, it can be concluded that the optimization of the number and spacing of the front metal fingers in the crystalline silicon solar cell is an efficient way to improve the electrical performance of the concentrating photovoltaic cell.

Omni-directional light capture in PERC solar cells enhanced by stamping hierarchical structured silicone encapsulation that mimics leaf epidermis.

Conventional crystalline silicon solar cell photovoltaic module technology requires much more development due to the challenges of efficiency loss and reliability problems such as browning damage. As an alternative to conventional ethylene-vinyl acetate (EVA)-glass encapsulation, silicone-based encapsulation is a promising innovation. Added to the many advantages of silicone based encapsulation for Si solar cells, here we present surface modification of silicone encapsulation with hierarchical structures inspired by leaf epidermis structures that improve light capture and hydrophobicity of the module surface using a simple, large-area silane and ozone treatment technique. The hierarchical structures comprise tens-of-micrometer-scale hills, valleys, and bump structures and sub-micrometer-scale wave patterns; the combination of these surface structures improved light transmission, light haze, and the wetting angle. These synergistic structures improve efficiency under vertical illumination compared to a bare cell, which is significant considering the efficiency loss in conventional EVA-glass encapsulation from those of bare cells. Furthermore, the enhancement increased the angle of incidence and improved the omni-directional performance so that electrical energy was generated more efficiently. We demonstrated that the modification of module surfaces by mimicking leaf epidermis structures yields considerable benefits, and further studies are expected to optimize this structure and identify the underlying principles for technological innovations based on silicone encapsulation.

Influence of backsheet materials on potential-induced degradation in n-type crystalline-silicon photovoltaic cell modules

We investigated the influence of backsheet materials on potential-induced degradation (PID) in n-type crystalline-silicon (c-Si) photovoltaic (PV) cell modules. Silicon heterojunction PV cell modules and rear-emitter n-type c-Si PV cell modules were fabricated by using aluminum backsheets composed of poly ethylene terephthalate (PET)/aluminum/PET as well as typical backsheets. PID tests of the modules were performed by applying a negative bias in a dry environment (<2% relative humidity). Regardless of the types of cells, the modules with the aluminum backsheets showed smaller degradation. This indicates that aluminum backsheets reduce PID effects, and to alter backsheets may be a potential measure to reduce PID.

Output power behavior of passivated emitter and rear cell photovoltaic modules during early installation stage: influence of light-induced degradation

The conversion efficiency of passivated emitter and rear cell (PERC) photovoltaic (PV) modules decreases via light-induced degradation (LID). In this study, two models of commercial PERC PV modules were employed. These modules were exposed outdoors until the accumulated solar irradiation reached 687 kW m−2 to investigate their power generation behavior during the early installation stage. The maximum output power (Pmax) finally decreased by 1.52% in one model and by 4.29% in the other model. Pmax of the latter model increased after LID owing to light-induced regeneration under open-circuit conditions. However, power generation in the array of the latter model connected to an electrical power grid was not changed after LID and no recovery was observed. It was found that the extent of degradation and the behavior differ depending on not only the difference in models but also the circuit conditions during exposure.

Stress and Fracture of Crystalline Silicon Cells in Solar Photovoltaic Modules – A Synchrotron X-ray Microdiffraction based Investigation

ABSTRACTFracture of crystalline silicon (c-Si) solar cells in photovoltaic modules is a big concern to the photovoltaics (PV) industry. Cell cracks cause performance degradation and warranty issues to the manufacturers. The roots of cell fractures lie in the manufacturing and integration process of the cells and modules as they go through a series of elevated temperature and pressure processes, involving bonding of dissimilar materials, causing residual stresses. Evaluation of the exact physical mechanisms leading to these thermomechanical stresses is highly essential to quantify them and optimize the PV modules to address them. We present a novel synchrotron X-ray microdiffraction based techniques to characterize the stress and fracture in the crystalline silicon PV modules. We show the detailed stress state after soldering and lamination process, using the synchrotron X-ray microdiffraction experiments. We also calculate the maximum tolerable microcrack size in the c-Si cells to sustain the residual stress after lamination. We further demonstrate the effect of these residual stresses on the cell fractures using the widely accepted fracture (4-point bending) tests. These test results show that the soldering and lamination induced localized residual stresses indeed reduce the load-carrying capacity of the c-Si cells.

The effect of non-uniformities in temperature on the performance parameters of an isolated cell photovoltaic module with a compound parabolic concentrator

The effect of non-uniformities in temperature on the performance parameters of an isolated cell photovoltaic module with a compound parabolic concentrator