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In this paper, we analyze the performance of a photovoltaic array implemented in the Universidad Politécnica de Valencia which consists of modules of different technologies and power, connected in series, in order to quantify the energy losses due to mismatch and the effect of the shadows. To do this, the performance of the modules was measured in...
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... Fcn output is a numerical value representing the voltage produced by the array formed by modules in series of the same type. In order to convert it into an electrical quantity, is applied to the control input of the controlled voltage generator. The 3 blocks are connected in series and the output is applied to a resistive load. The current is the same in all the blocks and the output voltage is the sum of the voltages generated by each block. The characteristics curves I-V and P-V of the photovoltaic system are obtained varying the input current and measuring the load voltage and power. Conditional blocks (If, If Action Subsystem) in order to avoid simulation error, producing no voltage if the current through a block is bigger than the short-circuit current. This fact happens by mismatch effect in systems with different types of modules, as in the present study; when a type of module produces a current bigger than the short-circuit current of another type, the bypass diodes connected in parallel with the less current module would drive, and the voltage through them would be almost zero. Figures 9 and 10 shows a power loss of about 20%. This result agrees with the experimental measures, because without mismatch effect the system would produce a total power of about 1900 W. The model could be modified to look for the optimum configuration, but these studies have already been reported in [1]. The study of shading effects is important to foresee the working point of a system in case of shading. When a module or a part of it is shaded some of its cells become reverse biased, acting as loads instead of generators. If the system is not appropriately protected, hot-spot problem can arise and, in severe cases, the system can be irreversibly damaged [7]. In this section the losses caused by shadings in a photovoltaic module are analyzed, using a monocrystalline panel Solar Plus of 40 W. The process consists in shading a cell of the panel and measuring the characteristic curves before and after the shading effect. In addition pictures with a thermographic camera were taken, measuring temperatures in different points of the panel and relating the panel power loss and the temperature increase. The shading effect was made evident in the thermographic camera capture using a black paper with an emissivity = 1. After shading a cell during several seconds the shade was removed, the results are shown in Figure 11, where is remarkable the heating of the shaded cell about to 55oC, also and a smaller heating of the next 3 chains of cells, caused by the change of the operating point of the shaded cell, that changes the behavior as a generator, to load. Figure 12 shows the characteristic curves of the panel before and after the shading. Power loss is significantly high, the module reduces the power from 40,33 W to 3,935 W, almost a 90 % of power loss caused by the shading effects. These curves agree with the behavior of a shaded panel [8] but with a much bigger loss, even after several minutes a bigger heating in the nearby cells of the shaded cell is observed, that can causes the module damage. These results suggest future studies and advances in shading effects, because power losses are in the range of (40% - 90%), causing big cost in the photovoltaic field, considering is still an expensive ...
Citations
... For high power output in an SPV cell, appropriate circuit equivalent values and appropriate SPV-cell materials are selected based on the use of solar radiation. In general, prominent SPV cell materials like monocrystalline and polycrystalline silicon (m-Si and p-Si), SPV-based materials have a high fill factor and conversion efficiency [1][2][3]. ...
In the last two decades, it is persistently emphasized to develop energy generation systems free from greenhouse gas emissions since these gases cause global warming, and it leads to unpredictable monsoons. Consequently, it might not be a conducive environment for human beings and animals to dwell. To ascertain the green environment for the next generations and reduce the use of fossil fuels, renewable energy sources are highly suggested to generate electrical energy. Solar photovoltaic is reckoned to be one of the promising methods to generate electricity; however, it has a lower conversion value due to various losses resulting from external and internal parameters. Among various losses that occurred in the solar photovoltaic system, mismatch loss is imperative, which causes the system to perform poorly. Solar photovoltaic systems have made topical advances in the use of highly effective solar cell materials to achieve high efficiency. In this analysis, performance parameters are influenced by the internal and external conditions of the solar photovoltaic systems and they lead to an increase in the loss of the system. The present review is focused to fetch fruitful information on the several studies that analyzed the effects on the solar photovoltaic systems of parasitic resistances, dust generated by tresses, clouds, solar radiation, temperature, relative humidity, different connection topologies, circuit implementation for partial shading, and remedies suggested by the potential authors.
... With the procedure described above, five multimodal functions were obtained representing the PeV curves of a PV module with multiple local maximums and a global maximum. This situation shows the performance of PV modules in partial shading conditions [3]. These types of functions are ideal for evaluating the performance of numerical optimization algorithms to find a global maximum [4,5]. ...
This paper presents the data of multimodal functions that emulate the performance of an array of five photovoltaic modules under partial shading conditions. These functions were obtained through mathematical modeling and represent the P-V curves of a photovoltaic module with several local maximums and a global maximum. In addition, data from a feedforward neural network are shown, which represent an approximation of the multimodal functions that were obtained with mathematical modeling. The modeling of multimodal functions, the architecture of the neural network and the use of the data were discussed in our previous work entitled "Search for Global Maxima in Multimodal Functions by Applying Numerical Optimization Algorithms: A Comparison Between Golden Section and Simulated Annealing" [1]. Data were obtained through simulations in a C code, which were exported to DAT files and subsequently organized into four Excel tables. Each table shows the voltage and power data for the five modules of the photovoltaic array, for multimodal functions and for the approximation of the multimodal functions implemented by the artificial neural network. In this way, a dataset that can be used to evaluate the performance of optimization algorithms and system identification techniques applied in multimodal functions was obtained.
... The objective was to use those models in developing control techniques for PV-islanded and grid-connected operation. The partial shading condition was discussed in some recent research papers [37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55]. It was found that the partial shading factor has the worst effect on the PV system performance, as it creates multiple maximum power points, which in turn causes the malfunction of the conventional maximum power point tracking system [56][57][58]. ...
In this chapter, the performance of PV systems in terms of maximum power point tracking (MPPT) is studied under the effect of different metrological conditions. Due to the obscurity and lack of credible solar irradiation information, it is important to estimate solar irradiation on horizontal and inclined surfaces by the use of a mathematical model, which considers meteorological data of the location under study. The proposed approach to develop this model is to estimate the global solar radiation on the inclined PV array, then dividing it into its main components. Each of the major metrological conditions affects the PV system performance by affecting a particular component of the total irradiance reaching it. This is thoroughly analyzed in detail in the sections of this chapter, mainly for partial shading conditions, angle of incidence, air mass, and dust. After that, the effect of each of the metrological conditions is modeled associated with a particular component of the global irradiance. Then, an aggregated irradiance model incorporating the effects of all the major metrological conditions is developed to show the reductions in the received irradiance and the generated power. Lastly, this chapter proposes an improved maximum power point tracking (MPPT) algorithm with variable step size, which is suitable for multiple maximum power points occurring during partial shading conditions.
... For example, when the irradiance on a cell is reduced due to shading, it impedes the flow of the electric current and limits the overall output of the module. These issues have been addressed in several studies of the shading effects in photovoltaic modules [2][3][4][5][6]. ...
We study the disproportional effect of non-uniformity on a system of photovoltaic cell network. When a cell is partially shaded, besides the loss from the shaded cell, the power output of the whole cell network is significantly affected. Although this effect is well known in the solar cell community, the theoretical analysis has relied on one or more approximations or specially defined functions. In this paper, we present a parametric formulation of photovoltaic cells in which the output voltage and current relationships are described by explicit functions parametrized by the voltage over the cell diode. No additional approximations or specially defined functions are required to study the output characteristics. We further show that the model remains unchanged when applied to a network of many identical PV cells either in parallel or in series; the parameters for the network can be obtained from those of the cell. Incorporating interpolation in calculation, the model can be used to study a network with dissimilar cells, specifically a network with a partially shaded cell. We show that the voltage over the shaded cell becomes negative and power is dissipated over the shaded cell. The model is also conveniently used to study the network output characteristics when bypass diodes are included in the PV network.
... The methods which discussed in this paper of partial shade problem [3,4] represent an efficient solution indicated in Guerrero et al. [5]. In this paper; full studying and comparing these three topologies by MATLAB/ Simulink had discussed. ...
... In this section, mathematical modeling of PV solar cell had been discussed [5]; this modeling allows us to study the power-voltage (P-V) curve and current-voltage (I-V) curve [6]. Figure 1 illustrates the equivalent circuit of PV solar cell. This paper chose a panel made by Philadelphia Solar Delivering Clean Energy Solutions Company product PS-M72H 315 W which its parameter included in Table 1 to make this study. ...
In this paper, detailed studying of the effect of partial shade on photovoltaic (PV) arrays, which represent one of the most well-known problems that affect this field of renewable energy, due to that matter, this paper discusses this issue and makes a detailed discussion for different connection topologies that used to increase the efficiency of the PV system under partial shade. This paper using MATLAB/Simulink to analyze three different connection topologies of PV modules under partial shade conditions (PSCs), these topologies are the series-parallel (SP) connection, total-cross-tie (TCT), and bridge linked (BL). The results in the study help the workers in this field to choose the best connection topology for PV power system and reach to that; the TCT topology is the best.
... It is well known that, in photovoltaic (PV) systems, mismatching due to partial shading, shadows of neighboring objects, dirtiness, clouds, different orientation angles of modules of the PV field, soiling, manufacturing tolerances, or ageing can cause reduced reliability and significant losses in the energy yield [1][2][3][4][5][6]. Even with the commonly used bypass diodes, mismatched cells may become reverse biased [7] and dissipate power, leading to dangerous localized heating phenomena called hot spots that in turn may cause accelerated ageing or even the damage of the cells. ...
... This is a general result. In the absence of mismatching conditions, the working of the PV system in the MPP is preferable for a two-fold reason: the maximization of the extracted power and the minimization of the aging effects that are, without exceptions, all intensified with the increase of the PV cell operating temperature [1][2][3][4][5][6]. A number of additional experimental characterizations confirming the above statement have also been carried out in different days and in different ambient operating conditions as concerns the irradiance level and the ambient temperature. ...
... A similar analysis has been carried out by artificially creating a mismatching condition as shown in Figure 6. It is well known that in PV systems, mismatching can be due to partial shading, shadows of neighboring objects, dirtiness, bird droppings, leaves, snow, clouds, different orientation angles of modules of the PV field, soiling, manufacturing tolerances, or ageing [1][2][3][4][5][6]. In particular, mismatching due to moving clouds and also to other possible moving bodies is characterized by both relatively fast dynamics (short duration) and also a relatively low degree of nonuniformity as concerns cell operating conditions. ...
Mismatching operating conditions negatively affect the extracted energy in photovoltaic (PV) systems. They may also lead to dangerous localized heating phenomena (hot spots) that can cause, in turn, accelerated ageing and reduced reliability. Since the adoption of bypass diodes or smart active switches does not prevent the occurrence of hotspots, it is necessary to investigate alternative strategies. A promising solution is represented by the proper regulation of the operating point of the PV cells in the current vs. voltage ( I - V ) or power vs. voltage ( P - V ) planes when mismatching conditions occur. In particular, in this paper, the existence of operating points allowing a suitable compromise between maximization of the extracted power and minimization of thermal stresses, due to hot spots, is experimentally evidenced. Experimental results highlighting the link existing between the operating point in the I - V plane and the PV cell temperature distribution under uniform and mismatching operating conditions are presented and discussed. On the basis of the obtained experimental results, it is possible to state that, when mismatching conditions occur, it is mandatory to properly choose the operating point: the global maximum power point may not be the best operating point. Hence, it is crucial to gain information about the eventual occurrence of mismatching conditions in order to be able to properly choose the best operating point. Therefore, another crucial aspect that is evidenced in this paper is represented by the fact that the detection of the occurrence of mismatching conditions, based on the analysis of the shape of the I - V and/or P - V characteristics, is effective only if the analysis is carried out for both positive and negative voltages.
... This problem raises serious concern and challenges to power-generation engineers who are assiduously proffering economic and viable technical solutions to this imminent problem. Shadows naturally emanate from the position of the sun relative to the earth; especially during the sunrise and sunset, shadows are probably to be casted by tall trees, towers, settlements and neighboring construction (Guerrero, Muñoz, Ibáñez, & Ospino, 2017;Ramaprabha & Mathur, 2012). Shadow produces total darkness which has overall devastating effect on power generation whereas moving clouds cause partial shading of the modules and pose less severity to power generation. ...
A comprehensive mathematical analysis of interconnected photovoltaic arrays under different shading conditions (opacity) and patterns (column, row, diagonal and corner) has been carried out in this work. The equivalent circuit models for the different shading conditions and patterns, and pseudocode algorithm were developed upon which the performance characteristics of the interconnected arrays were analyzed. Five different interconnections were inclusively considered in this work: series-parallel, total-cross-tied (TCT), bridge-linked, ladder and honey-comb interconnection. The emerging analytical results revealed that TCT is most dominant interconnection and shading patterns across the strings (row and diagonal) have detrimental effect on output power, especially when the opacity is one (signifying perfect shading condition) but shading patterns along the string (column or corner shadings) are less severe to power generation. The formation of double peaks sequel to the presence of shadings are inimical to power generated from the interconnected arrays. Moreover, increasing the interconnections enhances the output power and further serves as a means of bypassing current in the event of threats to the modules. Thus, the results obtained provide vital information for smooth operation and maximization of output power in interconnected arrays by avoiding shades on the strings.
... Shading as part of factors which can affect PV systems, is the main objective to be discussed in this paper. Many researchers have discussed about use of bypass diode in shading cases but the truth is that shading must be fully analysed and avoided because it can result in potential breakdown on the shaded module [11]. If it persists, it can result in harmful cases such as hot spots [12]. ...
... The effect of partial shading of PV-systems by obstacles such as trees and chimneys as well as for mobile applications is extensively studied in the literature, e.g. [20,50,67]. The net annual effect of the difference between applying string-or central inverters due to fast moving clouds therefore depends on the seasonal occurrence of partially clouded conditions, which will be very site dependent (for example desert vs. Northern Europe). ...
The work presented in this thesis addresses the optimization potential of large PV power plants with respect to energy production during periods of moving clouds. Presently the number and size of utility scale Photo Voltaic (PV) power plants in the megawatt range is increasing and the market for solar inverters is under a severe pressure regarding cost reduction. The main topic of this thesis is the investigation of the potential advantage of applying string inverters with multiple Maximum-Power-Point-trackers (MPPT) in large PV plants compared to the use of one large central inverter with one MPPT. The analysis is based on a comparative investigation of non-uniform irradiation events caused by moving clouds during a period of one year. A set-up for the long term recording of data from the 2.1 MW Danfoss Solar Park in Nordborg (DK) and the 62 kW PV plant at the University of Southern Denmark in Sønderborg (DK) was implemented. A total of 17 PV-inverters have been monitored during a period exceeding one year and the recorded data constitutes the basis of this investigation. A part of the 2.1 MW PV plant was reconfigured to emulate the behavior of a central-inverter and solar panels distributed over a distance of 160 m. In parallel a string based inverter configuration was established with solar panels at the same locations.
An analysis of irradiation data recorded during the test period showed that non-uniform irradiance due to moving clouds is expected to influence the PV plants for less than 4 % of their operational time. The resulting difference in energy production between a system with 3 MPPT and a system with 1 MPPT is calculated for all days where both systems had comparable operational conditions. It can be concluded that both the estimated and the calculated difference in the annual production of energy is in the range <0.3 % and around the limit of what can be registered in the PV plants. It has further been shown theoretically as well as experimentally that landscape variations result in energy production losses.
Two other methods were investigated by applying the recorded data from the 2.1 MW plant. The simulation of a dynamic string allocation concept for fast reallocation of PV strings in parallel show the potential of an increase in annual energy production of up to 0.6 %. The concept allocates PV strings in parallel during periods of low irradiation to avoid low inverter efficiency at low power levels. The effect of a sorting of the panels in the 2.1 MW park has been simulated to show the potential gain by applying PV sorting during the construction of a large PV plant. A sorting of the mounted PV panels is estimated to increase the annual energy production by approximately 0.4%.
A portable IV-scanning instrument for the fast long term characterization of solar panels was developed as part of the project. Each second a sweep of the IV-characteristics of a solar panel is performed and the result stored for later analysis. The instrument is based on an active load, is optimized for field use, is battery operated and has been applied for the characterization of a solar panel over a period of 6 months at the ESTER Outdoor PV monitoring station in Rome, Italy.
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.
