Shaded Cells Research Articles

A new algorithm described PV module’s behavior under partial shading conditions

The shadowing of a single cell in string leads to reverse bias of the shadowed cell. The cell acts as a load instead of a generator in order to deal with this effect and the hotspots problems, this paper focuses on the design of bypass diodes configuration and the behavior of a PV module (Suntech 85w) under partial shading divided from 36 cells into three parts of 12 cells and each part of these parts behaves like a single module, The effect of shadow has been simulated on this module, based on the transmission of shadow for a single shaded cell, before increasing the number of shaded cells for the same shadow transmittance, and the effect of the shaded on the unshaded module and those in the presence and absence of bypass diodes. The simulation results show that the consequences of the shading phenomena can be limited by this configuration and thus increase the operating efficiency of photovoltaic (PV) systems.

Effects of changing partial cell shading on the electrical and thermal characteristics of crystalline silicon photovoltaic module

Variable partial shading was used to analyse the electrical and thermal behaviour of 60 individual cells in an operational crystalline silicon (c-Si) Photovoltaic (PV) module by recording Thermal Infrared (TIR) images concurrently with electrical measurements of individual cells when shading levels between 0 and 100% were applied on one cell. This study investigated the relative changes in each of the individual cells’ operational cell voltage and the current of the substring containing the shaded cell. These changes are significant and can give additional insights into the loss of energy production of a module containing a shaded cell. The role of bypass diodes in mitigating these energy losses was also highlighted in this study. The bypass diode gets activated at 40% cell shading level and when the shading level increased from 40- to 100%, the operational voltage and current of the module remain unchanged while that of the shaded cell and substring containing the shaded cell is reduced. The operational temperature of the shaded cell increases to a maximum with an increase in shading level and drops when the substring’s bypass diode is activated. As expected, the substring containing the shaded cell tends to operate closer to open-circuit voltage (VOC) as the cells contribute less current than cells in unshaded substrings. The study gives insight into the performance of a c-Si module down to cell level under partial shading on real field conditions and can add value into the operation and TIR imaging of crystalline modules.

Parameter Estimation of the Bishop Photovoltaic Model Using a Genetic Algorithm

Photovoltaic panels can be affected by partial shading, which causes some shaded cells to consume the energy generated by other cells of the panel. That is, shaded cells stop operating in the first quadrant and start operating in the second quadrant, with negative voltage at their terminals, causing power losses and other negative effects in the cells. The Bishop model is an accurate representation of the cells behavior at the second quadrant, but estimating its parameters is not a trivial task. Therefore, this paper presents a procedure to estimate the parameters of the Bishop model by using the Chu–Beasley optimization technique. The effectiveness of this procedure was evaluated using different accuracy measures such as RMSE and MAPE, obtaining values lower than 0.5%. In addition, the results of this study demonstrate that it is essential to estimate all the parameters of the Bishop model, illustrate the variation in the parameters according to the cell technology and show the strong influence of the shunt resistance into the behavior at the second quadrant.

PV array reconfiguration according to shaded cells' number of every PV module

PV array reconfiguration according to shaded cells' number of every PV module

Design of shading‐ and hotspot‐resistant shingled modules

AbstractThe shingled module has become an attractive interconnection architecture for its higher packing density and superior power generation. However, with longer string lengths and smaller cell areas, these modules are particularly susceptible to developing hotspots from shading elements. In this paper, a framework for the design of hotspot‐ and shading‐resistant shingled modules is presented. An electrothermal model is developed and validated extensively through specially fabricated shingled modules that allow for string‐level measurement and analysis. To investigate the relative influence of cell electrical characteristics on power loss and hotspot temperature, we perform a stochastic Monte Carlo simulation which reveals a greater sensitivity to parameters associated with the shaded cell's leakage current. A further study on cells with illumination‐dependent Jleakage shows the detriment of this light‐induced effect where higher hotspot temperatures can develop. Module‐level parameters are also investigated where string length, number of parallel strings, and cell fraction are studied in relation to their impact on module power and hotspot response. Finally, these findings are condensed into a design matrix which defines the space in which module manufacturers may configure shingled modules such that hotspots will not exceed a set threshold temperature.

Designing Modules to Prevent Reverse Bias Degradation in Perovskite Solar Cells when Partial Shading Occurs

When a solar cell in a panel is shaded, the illuminated cells can place a large reverse bias on the shaded cell to attempt to force current through it. Although the panel can continue to produce power, the reverse bias can cause significant problems for the shaded cell. In the case of perovskite solar modules, Joule heating and irreversible electrochemical reactions will degrade the cell. Some photovoltaic technologies use bypass diodes to solve this problem. To prevent both a perovskite cell and an all‐perovskite tandem cell from falling into reverse bias breakdown while shaded, no more than two cells per bypass diode are allowed, which is likely to be prohibitively expensive for many applications. Herein, how many solar cells can be protected by one bypass diode in single‐junction and multijunction perovskite modules is explored. It is easier to incorporate bypass diodes into modules with singulated cells than with monolithic panels. It is shown that perovskite–silicon tandems can be protected with fewer bypass diodes than with single‐junction perovskite modules. It is suggested that if bypass diodes cannot be feasibly incorporated, then the panels should be deployed in utility‐scale power plants.

Modelling and Analysis of Photovoltaic System under Partially Shaded Conditions using Improved Harmony Search Algorithm

With the increasing penetration of solar electricity in residential, institutional and commercial centres around the globe, the phenomenon of partial shading (PS) in Photovoltaic (PV) power generation is gaining attention. Under Partial shading condition (PSC), cells that are shaded tends to have an equivalent current with cells that are unshaded in series-connection, due to this, the shaded cells operates in reverse bias and consequently becomes load and consumes the generated power. This causes a serious problem known as hotspot. This is characterized by the presence of excessive heat which consequently reduces the total generated power. Recently, researchers use the technique of bypass diodes across the PV cells so that the problem of partial shading can be reduced, but this solution taken alone, has made the nonlinearity and complexity of the system to increase. The shaded cells generate multiple peaks with only one global peak. Conventional Maximum Power Point Tracking (MPPT) algorithms do not differentiates the global peak from local peaks which may end up tracking local peak as global peak, this results in serious power loss. This paper seeks to solve this problem by modelling a PV system under PSC and through the application of Improved Harmony Search algorithm (IHSA) and variable step Perturb & Observe (P&O) to track the global peak instead of local peaks. Simulation was done in MATLAB/Simulink 2018a environment, and the results under standard test condition (STC) and PSC showed that the proposed IHSA had an improvement of 25%, 3.17% and 2.27%, 3.07% and 2.21%, 3.26% and 2.26% when compared with the improved particle swarm optimization (IPSO) under STC and PSC conditions respectively, which had a better advantage of minimizing power oscillation and improving the efficiency of the system, improved MPPT tracking, reduced error and a better tracking efficiency in both conditions.
 Keywords: MPPT, photovoltaic system, partial shading, tracking efficiency, Harmony search algorithm

Hot-spot generation model using electrical and thermal equivalent circuits for a copper indium gallium selenide photovoltaic module

Hot-spot generation is critical to the reliability and performance of copper indium gallium selenide (CIGS) solar cells; however, its occurrence mechanism has not been fully elucidated. We conducted a partial shade stress test on three large-area CIGS modules (156 cm × 62.6 cm in size, with 102 cells) connected in series. Partial shade stress can cause irreversible and unpredictable damage to the modules, and we confirmed the generation of hot spots on the shaded cells via infrared imaging. To emulate numerically the internal electrical and thermal changes in the shaded cells, we present electrical and thermal equivalent circuits based on the material properties and layered structure of the CIGS cells and modules. Furthermore, we propose a hot-spot generation model describing the irreversible damage to CIGS cells via shunt resistance degradation because the dissipated electrical power exceeds the threshold power (Pth). The current–voltage characteristics simulated by the presented method are congruent with those measured under partial shade conditions. Partial shade induces high electrical power consumption in the shaded cells, up to ~34 mW/cm2 at a 5% shade ratio, ~1,500 times higher than that in the unshaded cells. The shunt resistance is degraded to ~18.5 Ω/mm2 (only ~0.1% of the initial normal value), and the Pth-value is estimated to be ~2.4 mW/cm2 at the center of the hot-spot cells. The presented method and Pth-parameter can be used to evaluate durability with respect to the effects of partial shade stress for CIGS and various other thin-film photovoltaic cells and modules.

Modeling of Photovoltaic Modules Under Common Shading Conditions

Common shading conditions will leads to power loss and even result in hotspots, which influence the reliability of PV systems. Therefore, it is necessary to model for PV modules under common shading conditions in the PV station. Modeling of the shaded module relies on the appropriate model for the (partial) shaded cell. We observe that shaded region and unshaded region in a PV cell work quite differently. In the shaded region, the photoinduced current will decrease, and the shunt resistance will increase. In the unshaded region, the temperature rise can be even higher than 100 ℃. Consequently, it is essential to model for the shaded region and unshaded region respectively. In this paper, a physically explicable parallel model is proposed for the shaded cell and modeling of PV modules under common shading conditions are studied. We conduct extensive experiments, shading PV modules by area-measurable shade cloth with regular shape to analyze their I-V characteristics. PV modules are also shaded by uniformly accumulated dust, and leaf / soil / shadow with arbitrary shape and location to simulate the situation in real PV station. Experimental results verify the effectiveness of our method.

Monitoring of Photovoltaic System Performance Using Outdoor Suns-VOC

Summary In-field characterization of photovoltaics is crucial to understand performance and degradation mechanisms, subsequently improving overall reliability and lifespans. Current outdoor characterization is limited by logistical difficulties, variable weather, and requirements to measure during peak production hours. We capitalize on Suns-VOC, which is widely used for laboratory measurements of single solar cells and discuss the barriers in extending the technique to outdoor systems. We demonstrate the normalization of measurements using both backsheet temperature sensors and on-site weather stations. Despite weather variation, VOC, ideality factor, and pseudo fill factor all fall within 1% of the laboratory measurements. It is also demonstrated that monitoring the system VOC at 0.05 to 0.1 suns, during minimal power production, provides a figure of merit that can indicate early degradation of the system. Extensive simulations show that shading portions of a system has minimal effect on measurements, allowing the technique to be used in all weather conditions.

Shading fault detection in a grid-connected PV system using vertices principal component analysis

Partial shading severely impacts the performance of the photovoltaic (PV) system by causing power losses and creating hotspots across the shaded cells or modules. Proper detection of shading faults serves not only in harvesting the desired power from the PV system, which helps to make solar power a reliable renewable source, but also helps promote solar versus other fossil fuel electricity-generation options that prevent making climate change targets (e.g. 2015’s Paris Agreement) achievable. This work focuses primarily on detecting partial shading faults using the vertices principal component analysis (VPCA), a data-driven method that combines the simplicity of its linear model and the ability to consider the uncertainties of the different measurements of a PV system in an interval format. Data from a grid-connected monocrystalline PV array, installed on the rooftop of the Power Electronics and Renewable Energy Research Laboratory (PEARL), University of Malaya, Malaysia, have been used to train the VPCA model. To prove the effectiveness of this VPCA method, four partial shading patterns have been created. The obtained performance has, then, been tested against a regular PCA. In addition to its ability to acknowledge the uncertainty of a PV system, the VPCA method has shown an enhanced performance of detecting partial shading fault in comparison with the standard PCA. Also, included in the article is an extension of the contribution plot diagnosis-based method, of the Q-statistic, to the interval-valued case aiming to pinpoint the out-of-control variables.

Partial shading of one solar cell in a photovoltaic module with 3-terminal cell interconnection

We examine the electrical and thermal characteristics of a photovoltaic module with three-terminal cell interconnection when partially shading a solar cell by experimentally verified modeling. For the interconnection of multi junction and tandem solar cells a two- (2T), three- (3T), and four-terminal (4T) cell architecture is conceivable. The 3T architecture featuring a combination of parallel and series interconnection combines the advantageous of 2T and 4T cells without their drawbacks. We build a photovoltaic (PV) module with silicon solar cells in a 3T tandem solar cell interconnection configuration (3TTSC PV module) to emulate a solar module with 20 3TTSC. To the best of our knowledge, no 3TTSC PV module with more than five solar cells has been shown in previous studies. We measure the effect of partially shading a 3TTSC in this module and develop an electrical simulation to model our experimental results. In the simulations we determine the dissipated power in the top and bottom cells due to the current mismatch caused by partial shading. Our results reveal that the shaded top and bottom cell as well as the adjacent top cell dissipate power when a single 3TTSC is shaded. The two top cells share the dissipated power. Our simulated power dissipation correlates with temperature measurements of the 3TTSC PV module in a steady-state sun simulator. Therefore, in a 3TTSC PV module the temperature of a shaded cell is lower than in a module with 2T configuration. This is an advantage of PV modules with 3T tandem solar cells in terms of reliability and long-term stability.

Mono-crystalline silicon photovoltaic cells under different solar irradiation levels

In this research, partial shading influences on the efficiency of photovoltaic modules are explored. First, mathematical modeling of the Mono-crystalline PV module in case of various irradiation levels is presented. A performance assessment of a PV module by considering the electrical influence of the partial shading are then presented. The PVSYST software is used to explain the behavior of a cell or a group of shaded cells in a PV module. The tool allowed a good understanding of the functions of shunt diodes when one or more cells are shaded. Finally, this simulation is applied to the Algerian site of Béchar. In spite of shadowing and an inclination of 30°, the obtained results are good along the year with a maximum power point. The simulation has given the maximum of energy.

One, two, three, thrive.

It was a sunny Friday afternoon, and my smiling labmates were heading home for the weekend. I, however, was glumly sitting in Tristan's office, staring at the spreadsheet on which we had outlined our goals for the week. I shaded my cells red; I had not been able to complete any of them. I was disappointed in myself. Tristan gave me a reassuring smile, reminding me not to beat myself up too much. “It's OK to be ambitious, but make sure your three weekly goals are realistic and measurable,” he advised. It was guidance I was still learning to follow.

Bypass diode effect on temperature distribution in crystalline silicon photovoltaic module under partial shading

Partial shading of photovoltaic (PV) system is commonly observed in the outdoor field conditions. The non-uniform illumination causes mismatch in the electrical output between the cells, which results in a non-uniform temperature distribution that can have an instantaneous effect on power and long term effect on reliability. The objective of present work is to study the temperature distribution in a partially shaded PV module under the inactive and active state of bypass diode. In this work, an electro-thermal PSPICE model has been developed to estimate temperature distribution in a shaded PV module. The temperature distribution in shaded module is analyzed in terms of number of shaded cells and their shaded area. An experimental setup has been designed to validate the developed model. To analyze the impact of different shading conditions in outdoor, thermal shade impact factor has been derived in the present study. The thermal shade impact factor can be used to estimate temperature gradient and its distribution in a shaded PV module, when the state of bypass diode changes from inactive to active. The results show that shading conditions that have thermal shade impact factor less than −1 will result in amplification of temperature gradient, when the state of bypass diode changes from inactive to active. This will lead to a manifold increase in the temperature of shaded cell. On the other hand, shading conditions which have thermal shade impact factor greater than −1 exhibit higher temperature gradient when bypass diode is inactive.

OPERATION PERFORMANCE ENHANCEMENT OF MULTIPLE RENEWABLE ENERGY SOURCES CONNECTED TO GRID SYSTEM

Solar photovoltaic (PV) clusters in versatile applications are regularly subject to incomplete shading and quick vacillations of shading. In the standard arrangement associated wiring plan, the lingering vitality produced by in part shaded cells either can't be gathered (if diode skirted) or, more terrible, obstructs accumulation of intensity from the rest of the completely lit up cells (if not circumvent). By and large, there will exist different neighbourhood MPPs, and their qualities will change as quickly as does the light. In this paper, a sun based PV framework that successfully kills both of the previously mentioned issues is portrayed and demonstrated. This framework is prepared to do at the same time boosting the power created by each PV cell in the PV board. The proposed design comprises of a variety of parallel-associated PV cells, a low-input-voltage venture up control converter, and a straightforward wide transfer speed MPP tracker. Parallel-designed PV frameworks are contrasted with conventional arrangement arranged PV frameworks through both equipment analyses and PC reproductions in this paper. Study results exhibit that, under complex irradiance conditions, the power produced by the new arrangement is roughly twice that of the conventional setup. The sun powered PV framework can be broadly utilized in numerous shopper applications, for example, PV vests for mobile phones and music players.

Mitigation of mismatch losses in solar PV system – Two-step reconfiguration approach

Photovoltaic system encounters with some limiting factors such as partial shading that reduces the power output. Partial shading is not predictable; not measurable; and unavoidable. A single partial shaded PV cell limits the power output of the unshaded PV cells connected with it in series. In this paper, a hybrid reconfiguration algorithm has been proposed. The 4 × 4 PV array has connected in Total Cross Tied configuration. The proposed algorithm performs reconfiguration in two steps. In the first step, the algorithm splits the 4 × 4 PV array into two sets of 2 × 4 PV arrays and it establishes the interconnection between the two sets by through the 2 × 2 switching matrix circuit in the second step. The interconnection will be executed based on the power generation of each row in the 2 × 4 PV arrays i.e., the maximum power generating row in the set 1 has connected with the minimum power generating a row in set 2. By this reconfiguration, the rows in the PV array can be made as even current generating rows. The proposed method suppresses the effect of partial shading in the power output also it reduces the required numbers of switches and the dimension of the switching matrix circuit.

Deterioration Diagnosis of Solar Module Using Thermal and Visible Image Processing

Several factors cause the output degradation of the photovoltaic (PV) module. The main affecting elements are the higher PV module temperature, the shaded cell, the shortened or conducting bypass diodes, and the soiled and degraded PV array. In this paper, we introduce an image processing technique that automatically identifies the module generating the hot spots in the solar module. In order to extract feature points, we used the maximally stable extremal regions (MSER) method, which derives the area of interest by using the inrange function, using the blue color of the PV module. We propose an effective matching method for feature points and a homography translation technique. The temperature data derivation method and the normal/ abnormal decision method are described in order to enhance the performance. The effectiveness of the proposed system was evaluated through experiments. Finally, a thermal image analysis of approximately 240 modules was confirmed to be 97% consistent with the visual evaluation in the experimental results.

ALGORITHM FOR SOFTWARE IMPLEMENTATION OF DESIGNING OVERVOLTAGE PROTECTION IN PHOTOVOLTAIC MODULES OF SOLAR ARRAYS USING A VARISTOR-POSISTOR STRUCTURE

The use of modern hardware and software design allows to effectively solve a number of problems associated with the development of various technical devices. The specificity of this approach is the development of algorithms with the capabilities of dynamic correction of the design process with the participation of the user. The algorithm of the software implementation of designing protection circuits against electrical overloads in photovoltaic modules of solar arrays using a voltage limiting device based on metal oxide varistor and posistor of the PolySwitch type being in thermal contact is described in this paper. The algorithm provides for determining the optimal technical parameters of the voltage limiting device (minimum resistance and tripping current of the posistor element, classification voltage and non-linearity coefficient of the varistor element) for the operation of photovoltaic module, which is in the state of lighting in the absence and presence of faulty, degraded, or shaded photovoltaic cells.

Cascaded Multilevel PV Inverter With Improved Harmonic Performance During Power Imbalance Between Power Cells

The difference in power cell irradiances in cascaded multilevel converters results in different duty cycles among those cells when maintaining the maximum power point tracking (MPPT). However, the difference in cell duty cycles is undesired since it is proportional to the output voltage and current distortions. To this regard, a multilevel topology for photovoltaic (PV) applications is proposed, where an H6 bridge power cell is used instead of an H-bridge one. In case of solar irradiance mismatch among the power cells, the proposed converter injects power with lower voltage from the shaded cells without altering the PV voltage; hence maintaining the MPPT operation. This modification allows us to retain an equal duty cycle in all the power cells whatever the meteorological conditions are present; consequently, maintaining good output voltage and current waveform qualities. To test the effectiveness of the proposed solution, a detailed simulation model as well as an experimental prototype is built. The obtained results show that the proposed topology provides significantly improved output voltage and current qualities compared to the cascaded H-bridge one. The performance of the proposed topology compared to one offering improved harmonics performance, according to the European efficiency, has been also compared, where an enhancement of 2.64% has been registered.