Article

A new topology to mitigate the effect of shading for small photovoltaic installations in rural sub-Saharan Africa

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Abstract

Many field researchers have in the past grappled with the problems of energy loss and panel damage as a result of shading and staining of PV panels after installation. A number of solutions have been proposed to try and minimize the effects of this problem in the field. The problem with all these solutions is that they address inter-panel connection topologies for very large installations. No particular attention has been paid to the topologies of individual panels. In sub-Saharan Africa most installations are single panel solar home systems and therefore small shading can result in an entire installation being disabled.This paper aims to study the effect of shading and staining on photovoltaic modules and propose a new topology that will reduce the effect of shading on the performance of individual photovoltaic modules.

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... The efficiency improvement of operating PV systems has become a research target. Abnormal operation of a PV system is often the cause of major power loss and, at worst, of zonal or total destruction of solar modules [13,16,21,23]. ...
... Table 3 Comparison between the results obtained from measurements and from the three models Eqs. (12), (23), and (26). Table 3 summarizes the results of measurements and calculations obtained using the three models. ...
... Eqs. (12), (23), and (26) with the experimental values associated to our application. The model equation with the quadratic terms (Eq. ...
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... The efficiency improvement of operating PV systems has become a research target. Abnormal operation of a PV system is often the cause of major power loss and, at worst, of zonal or total destruction of solar modules [13,16,21,23]. ...
... Table 3 Comparison between the results obtained from measurements and from the three models Eqs. (12), (23), and (26). Table 3 summarizes the results of measurements and calculations obtained using the three models. ...
... Eqs. (12), (23), and (26) with the experimental values associated to our application. The model equation with the quadratic terms (Eq. ...
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This paper presents a novel application of the Design of Experiments (DoE) method as a practical method to detect any dysfunction of an operating photovoltaic (PV) panel. Electrical field measurements data are used to evaluate the PV panel parameters once and for all. A mathematical model describing the variations of the maximum power versus solar irradiance level and temperature was obtained with the Design of Experiments method. This model is a predictive model. It assesses the value of the maximum power delivered anywhere in the experimental domain. Given a known solar irradiance level and temperature, any discrepancy between the calculated and measured maximum power values signals any dysfunctional operation so that appropriate action can be taken such as maintenance or repair. A complete analysis of the measurements is performed to optimize the method. Firstly, the basic elements of the Design of Experiments method are presented. Three models are then considered: the non-standard model with four trials, the non-standard model with 11 trials, and finally a model with 4 points recalculated to be placed at the vertices of the study area. A practical method of implementation is then proposed.
... The original DIRECT algorithm divides all potential optimal to search for the GP globally and locally at the same time. But the dividing strategy is different [53], [54], thus the conditions are explained mathematically [52]. ...
... With the help of change in duty cycle (19) and (20), the tracking efficiency and speed of partially shaded conditions are 0.5% less than the STC. If number of cycles are more per second then the efficiency and tracking speed are more [54]. ...
... The unshaded cell in then forced to produce less energy. In this situation there is no risk of destruction and the MPPT will tend remain in it while the shadow is cast over the PV module [Ubisse andSebitosi, 2009, Picault et al., 2010b]. Now that the effects of the shadow have been introduced, this chapter takes a closer look at what shadow is and how it can be modeled from a PV perspective. ...
... Third, there is no consensus in the literature. Some authors only take the geometry of the shadow into consideration [Picault, 2010, Wang and Hsu, 2009, Ubisse and Sebitosi, 2009, Drif et al., 2008, Fujisawa and Ohya, 2003, Kovach and Schmid, 1996. While others focus themselves on the opacity of the shadow [Alonso-Garcia et al., 2006, Safari and Mekhilef, 2011, Ramos-Paja et al., 2010. ...
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Photovoltaic energy rates among the most mature renewable sources currently available in the market. However, its growing use in urban environment has met with an important obstacle: shadows. Their study present a two-fold challenge: understanding what they are and how they can be mitigated. While many authors have proposed different solutions for this problem, very few have tried to understand the shadow in its complexity. This thesis seeks, at the same time, a comprehensive view on the shadow itself while proposing a new solution to mitigate it. The comprehensive view of the shadow is proposed through an intermittency theory, where its optical properties and electrical consequences are taken into account. This theory provides the elements to review the current literature into a new perspective. The available solutions are, then, divided into two families: series and parallel. Series solutions employ several structures, each extracting the power of a reduced number of photovoltaic cells. As a consequence the impact of the shadow is restricted. Parallel solutions use few structures to redistribute the current between shaded and unshaded photovoltaic cells, thus sharing the impact of the shadow. The new solution proposed to mitigate the shadow is a parallel system called PV Equalizer. Inspired from its battery equivalent, it has a different topology with a high integration potential, easily scalable but seemingly difficult to control. To prove its concept, a study is conducted to determine its functions. It is found to be capable of not only mitigating but also detecting the shadow. These functions are characterized and their results used to conceive a control algorithm. Finally, this algorithm is tested and validated in a prototype under real operating conditions. The system detected the presence of the shadow, chose the best way to mitigate it and raised the power output by roughly 40 %.
... The unshaded cell in then forced to produce less energy. In this situation there is no risk of destruction and the MPPT will tend remain in it while the shadow is cast over the PV module [Ubisse andSebitosi, 2009, Picault et al., 2010b]. Now that the effects of the shadow have been introduced, this chapter takes a closer look at what shadow is and how it can be modeled from a PV perspective. ...
... Third, there is no consensus in the literature. Some authors only take the geometry of the shadow into consideration [Picault, 2010, Wang and Hsu, 2009, Ubisse and Sebitosi, 2009, Drif et al., 2008, Fujisawa and Ohya, 2003, Kovach and Schmid, 1996. While others focus themselves on the opacity of the shadow [Alonso-Garcia et al., 2006, Safari and Mekhilef, 2011, Ramos-Paja et al., 2010. ...
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Photovoltaic energy rates among the most mature renewable sources currently available in the market. However, its growing use in urban environment has met with an important obstacle: shadows. Their study present a two-fold challenge: understanding what they are and how they can be mitigated. While many authors have proposed different solutions for this problem, very few have tried to understand the shadow in its complexity. This thesis seeks, at the same time, a comprehensive view on the shadow itself while proposing a new solution to mitigate it. The comprehensive view of the shadow is proposed through an intermittency theory, where its optical properties and electrical consequences are taken into account. This theory provides the elements to review the current literature into a new perspective. The available solutions are, then, divided into two families: series and parallel. Series solutions employ several structures, each extracting the power of a reduced number of photovoltaic cells. As a consequence the impact of the shadow is restricted. Parallel solutions use few structures to redistribute the current between shaded and unshaded photovoltaic cells, thus sharing the impact of the shadow. The new solution proposed to mitigate the shadow is a parallel system called PV Equalizer. Inspired from its battery equivalent, it has a different topology with a high integration potential, easily scalable but seemingly difficult to control. To prove its concept, a study is conducted to determine its functions. It is found to be capable of not only mitigating but also detecting the shadow. These functions are characterized and their results used to conceive a control algorithm. Finally, this algorithm is tested and validated in a prototype under real operating conditions. The system detected the presence of the shadow, chose the best way to mitigate it and raised the power output by roughly 40 %.
... In other words, the current-voltage (I-V) curves of modules must be similar. For instance, if a shadowed or damaged solar cell in a string causes that the cell produces current lower than the other cells then it will block the current flow from healthy cells to the output terminal of the string [1][2][3]. The generating current of solar cell depends strongly on irradiance level. ...
... The proposed method is intended to find the global MPPs under the non-uniform operating conditions. This is very difficult for classical MPPT controllers [3,34]. In this reason, an intelligent technique is required [1]. ...
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Mismatching losses reduction of photovoltaic (PV) array has been intensively discussed through the increasing penetration of residential and commercial PV systems. Many causes of mismatching losses have been identified and plenty of proposed methods to solve this problem have been recently proposed. This paper deals with reducing method of mismatching losses due to the non-uniform irradiance conditions. It is well-known that a certain number of multiple peaks occur on the power–voltage curve as the number of PV modules in one-string increases under non-uniform operating conditions. Since the conventional control method only drives the operating points of PV system to the local maxima close to open circuit voltage, only small portion of power can be extracted from the PV system. In this study, a radial basis function neural network (RBF-ANN) based intelligent control method is utilized to map the global operating voltage and non-irradiance operating condition in string and central based MPPT systems. The proposed method has been tested on 10 × 3 (2.2 kW), 15 × 3 (2.5 kW) and 20 × 3 (3.3 kW) of series–parallel PV array configuration under random-shaded and continuous-shaded patterns. The proposed method is compared with the ideal case and conventional method through a simple power–voltage curve of PV arrays. The simulation results show that there are significant increases of about 30–60% of the extracted power in one operating condition when the proposed method is able to shift the operating voltage of modules to their optimum voltages.
... In other words, the current-voltage (I-V) curves of modules must be similar. For instance, if a shadowed or damaged solar cell in a string causes that the cell produces current lower than the other cells then it will block the current flow from healthy cells to the output terminal of the string [1][2][3]. The generating current of solar cell de- pends strongly on irradiance level. ...
... The proposed method is intended to find the global MPPs under the non-uniform operating conditions. This is very difficult for clas- sical MPPT controllers [3,34]. In this reason, an intelligent tech- nique is required [1]. ...
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... The research process begins with the selection of a location. The parameters used to select the site are accessible to solar irradiance and minimum environment shading conditions (Ubisse & Sebitosi, 2009). Once the site is selected, observation is done to determine the building's energy consumption and surface availability. ...
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... External conditions, such as the effect of solar panel shading and a country's solar spectrum are vital to consider when designing solar panels, as their optimisation could improve energy generation capacity (Simon & Meyer, 2008;Ubisse & Sebitosi, 2009). For example, a higher capacity system was required in one region of South Africa compared to another, in order to generate the same amount of energy, which was attributed to solar irradiance differences (Azimoh, Klintenberg, Wallin, & Karlsson, 2015b). ...
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Solar home systems (SHSs) have seen rapid growth and have proven to be a viable source of electricity for households due to their capability to reach remote users that do not have access to grid systems. Based on a comprehensive literature review of 139 papers focussing on SHSs in Sub-Saharan Africa, this paper highlights the key trends, research gaps and policy recommendations. The literature was categorised into four themes: institutional, technology, viability and user-centric. The review finds that the current primary themes of research are technology, user-centric and viability. This highlights the need for further research into the institutional barriers of SHSs, as well as the regulatory frameworks and incentives needed to increase their adoption. The most popular topics discussed in the reviewed literature included SHS business models, SHS design, the energy demand of end-users and barriers to SHS adoption. The authors also identified paucity of research in countries with low electrification rates, highlighting new locations for SHS research.
... Several studies and research studies have evaluated the performance of photovoltaic modules in different climatic conditions, in particular the effect of sand dust accumulation and partial shading on energy loss in photovoltaic modules and arrays [14][15][16][17][18][19][20][21]. ...
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Usually, manufacturers provide PV panels, accompanied with data measured under Standard Test Conditions (STC), i.e. determined at AM1.5 with an irradiance of 1000W/m2 and a cell temperature equal to 25 C. In fact, these conditions do not reflect the reality of natural operation of PV panel conditions and these functional data associated with the real panel operating point may vary from one environment to another due to the change in weather conditions. The characterization of different types of PV panels under natural conditions of operation is, therefore, necessary in order to have a global view about the true electrical performance of different technologies at a given site. This work evaluates the influence of climatic conditions on the behavior of QS-60DGF module which has been installed at the Unit of Research in Renewable energy URERMS Adrar in the southern Algeria. The degradation evaluation of QS-60DGF module with different defects was performed, using (I-V/P-V) characteristics under daily weather conditions and the the visual inspection such as glass breakag. This study is to investigate the degradation rates of a-Si PV module after more than one year of outdoor exposure in desert conditions.
... Therefore, it is necessary to quantify the shading losses through a combination of the geometric shading factor and its electrical impact on the PV array, which leads to an effective shading factor (FES). Several methods already exist to transform the geometric shading factor into the effective shading factor (Kawamura et al., 2003;Alonso-García et al., 2006;Karatepe et al., 2007;Karatepe et al., 2008;Silvestre and Chouder, 2008;Ubisse and Sebitosi, 2009;Ishaque et al., 2011;Wang and Hsu, 2011;Rodrigo et al., 2013;Díaz-Dorado et al., 2014), many of which are based on I-V curves. ...
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Photovoltaic (PV) systems can be affected by complex shading. Software solutions have been developed over time, offering an ever-increasing set of simulation possibilities to evaluate the energy losses induced by shading on PV systems. Yet, several practical cases cannot be satisfactorily solved by means of existing tools. This study explores the possibilities offered by the powerful graphics processing units (GPUs) that have been developed for the video game industry. It is shown that complex shading problems applicable to PV systems can be satisfactorily analyzed, both visually and quantitatively, with a focus on the rasterization process for an in-depth evaluation of the shading dynamics that affect the direct component of solar irradiance. This analysis can be conducted at high spatiotemporal resolution for maximum accuracy. Its application is illustrated based on several practical cases that are typically encountered in the world of PV systems engineering, such as building-integrated PV (BIPV) on large and complex buildings, urban PV planning, or PV plants equipped with tracking systems and installed on uneven ground. Additional advantages are also presented, including the full integration of the GPU-based shading simulation tool into a Web browser, and the use of online input information.
... Many rural electrification assessment studies have been conducted. Some studies evaluate a technology to be used to promote rural electrification; examining its components, analyzing performance potential, and assessing the performance of the system in the targeted rural communities (Huacuz et al., 1995;Krauter, 2004;Mukerjee, 2007;Heal, 2009;Shaahid and El-Amin, 2009;Ubisse and Sebitosi, 2009;Pappas, 2012). Such studies address the economic and technical aspects (and viability) of the technologies used to promote rural electrification. ...
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... The aging and degradation of photovoltaic modules is also dependent on climatic and environmental conditions [12,13]. Several research works and studies have treated the evaluation of the performance of photovoltaic modules under different climatic conditions, in particular the effect of sand dust accumulation and partial shading on the power loss in photovoltaic modules and arrays [14][15][16][17][18][19][20][21]. The objective of this work is to study the effect of partial shading and deposition of sand dust on power loss in photovoltaic modules (ISOFOTON 100), we perform also experimental investigation of the effect of varying temperature and irradiation on PV performance parameters for one day. ...
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... The use of sophisticated controllers to enhance performance of SHS has been achieved in a study like [34]. Bypassed diodes has been used to mitigate the effect of shading, thereby maintaining the power quality of a shaded solar panels [35]. Most of these solutions concentrated on the technical design of solar panels and its paraphernalia. ...
... Shading panels greatly reduce system performance and output power presents several maxima [2], while tracking algorithms of the Maximum Power Point (MPPT) are usually based on the assumption that the power curve generated has a single peak [3,4,1,5]. In recent years, the impact of shading on the energy performance of photovoltaic systems has been discussed [6][7][8]. Before attempting to eliminate or reduce the effects of mismatch, a deep understanding of their origin and behavior is necessary. Since field tests are long term, costly, and highly dependent on climatic conditions, it is necessary to define a simulation-based model that allows proper inclusion of the shading effects. ...
... Output power changes of grid-connected PV systems due to moving clouds, inducing rapid changes in irradiance incident on the PV array, is studied in [15]- [17]. Methods have been proposed for improving PV system performance under partial shading conditions, mainly focusing on alterations of PV array configuration in terms of bypass diode number [18] and string connection patterns [19]. ...
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... Such problems have presumably not been reported in recent literature on account of technological development in inverters and other electronic and electrical balance of systems. One of the recent studies has highlighted the impact of shading and staining on overall energy loss for single module solar home systems that are largely found in Africa and other developing countries [153] . According to this paper, the inter-panel connection topologies for very large installations are addressed to some extent by researchers world wide. ...
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This paper applies a new dynamical electrical array reconfiguration strategy on the photovoltaic (PV) panels arrangement based on the connection of all PV panels on two parallel groups to reach the 24 V requested by the considered load and providing a maximum output current by connecting in serial the two groups. If one of the PV panels or more is shaded, the connection of the other in the same group will be automatically modified to maintain the requested 24 V for each PV panel row. This dynamical reconfiguration allows also reducing the lost power, due to the shaded panel, by recovering this power from the reconfiguration of the other panels. As a result, a real time adaptation of switch matrix allows a self-ability to maintain a constant voltage at 24 V and minimum number of PV panels is switched off by isolating the effect of shaded panels. In addition, the proposed solution can also be applied for the dirty panel and identify the shaded, dusty and faulty panel.
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ABSTRACTA process to fabricate a parallel connection dye‐sensitized solar cell (DSSC) module has been developed using commercially available materials and screen printed silver grid. The process is not only simple but also easy to manipulate and therefore facilitates researchers in evaluating new materials in a module platform. By changing the design of the silver grid pattern, it was found that the performance of DSSC modules can be controlled. With the silver grid, DSSC modules have shown that a 7% conversion efficiency can be reached. Modules fabricated by this process, but with a non‐volatile electrolyte system, passed a 60 °C, 1000 h thermal aging test. Copyright © 2012 John Wiley & Sons, Ltd.
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Photovoltaic (PV) solar energy is the solution combining economy and efficiency for the supply of stand alone systems. This combination can only be achieved by taking into account the effects of shading which have dramatic consequences on the electrical power delivered. In this paper, we present an experimental study of the effect of shading PV array on a pumping system performance. The experimental bench is installed at the Industrial Technology and Information Laboratory (LTII) in Bejaia (Algeria). In order to test the performances of the proposed system we propose different array configurations which show different behaviors against partial shading conditions. Shadow impacts fundamentally the global PV pumping system production; its influence is difficult to model because it depends on many parameters such as the configuration of the PV array, the relative rate of shadow, and the shaded area of the module. In general, it is better to have a completely shaded string than several partially shaded ones. These are ones of the most important conclusions obtained in this work.
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A general method for modeling typical photovoltaic (PV) arrays and modules is proposed to find the exact current and voltage relationship of PV arrays or modules of geometrically and electrically different configurations. Nonlinear characteristic equations of electrical devices in solar array or module systems are numerically constructed without adding any virtual electrical components. Then, a robust damped Newton method is used to find exact I–V relationship of these general nonlinear equations, where the convergence is guaranteed. The model can deal with different mismatch effects such as different configurations of bypass diodes, and partial shading. Geometry coordinates of PV components are also considered to facilitate the modeling of the actual physical configuration. Simulation of a PV array with 48 modules, partially shaded by a concrete structure, is performed to verify the effectiveness and advantages of the proposed method.
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In order to help keep readers up-to-date in the field each issue of Progress in Photovoltaics will contain a list of recently published journal articles most relevant to its aims and scope. This list is drawn from an extremely wide range of journals, including IEEE Transactions on Electron Devices, Journal of Applied Physics, Applied Physics Letters, Progress in Photovoltaics and Solar Energy Materials and Solar Cells. To assist the reader, the list is separated into broad categories, but please note that these classifications are by no means strict. Also note that inclusion in the list is not an endorsement of a paper's quality.
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This paper proposes a single-stage three-phase photovoltaic (PV) system that features enhanced maximum power point tracking capability, and an improved energy yield under partial shading conditions. Further, the proposed PV system can effectively double the maximum permissible dc voltage of a grounded conventional single-stage PV system, with no need for insulators, fuses, disconnects, and switchgear of a higher voltage class, with respect to safety/insulation standards or common system integration practices exercised for conventional grounded single-stage PV systems. The proposed PV system is realized through the parallel connection of an auxiliary half-bridge converter to the dc link of a conventional single-stage PV system and, therefore, is also an option for retrofit applications. This paper presents the mathematical model, principles of operation, and the control loops of the proposed single-stage PV system. The performance of the proposed single-stage PV system is demonstrated by time-domain simulation studies conducted on a detailed switched model in the PSCAD/EMTDC software environment.
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The electrical characteristics of array interconnection schemes are investigated, using simulation models to find a configuration that is comparatively less susceptible to shadow problems and power degradation resulting from the aging of solar cells. Three configurations have been selected for comparison: simple series-parallel (SP) array, which has zero interconnection redundancy; total-cross-tied (TCT) array, which is obtained from the simple SP array by connecting ties across each row ofjunctions and which may be characterized as the scheme with the highest possible redundancy; and bridge-linked (BL) array, in which all cells are interconnected in bridge rectifier fashion. The explicit computer simulations for the energy yield and current-voltage distributions in the array are presented, which seem to favor cross-tied configurations (TCT and BL) in coping with the effects of mismatch losses.
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A new method of measurement of series resistance Rs and shunt resistance Rsh of a silicon solar cell is presented. The method is based on the single exponential model and utilizes the steady state illuminated I–V characteristics in third and fourth quadrants and the Voc–Isc characteristics of the cell. It enables determination of values of Rsh and Rs with the intensity of illumination. For determination of Rs it does not require Rsh to be assumed infinite and realistic values of Rsh can be used. The method is very convenient to use and in the present study it has been applied to silicon solar cells having finite values of Rsh. We have found that Rsh is independent of intensity but the Rs decreases with both the intensity of illumination and the junction voltage.
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The authors have developed the sophisticated verification (SV) method, which can evaluate involving performance ratio, power conditioner efficiency, temperature factor, shading factor, load matching factor and other array parameter. So, we also have ensured adequacies of the evaluation of PV systems. However, the originally proposed method accepts PV installations facing the south only. In this paper, we have modified the SV method by taking into account the arbitrary orientation and inclination, because of improved the accuracy of evaluation. Therefore, the shading effect can be intelligible for each hour. The maximum value of shading losses reached 13.1%.
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The models for photovoltaic (PV) systems currently in ESP-r prove very useful in estimating the electrical and thermal impact of building-integrated photovoltaics. However, while they represent well the impact of photovoltaics on the building's thermal energy balance, they may lack in accuracy in the prediction of the system's energy production. To achieve both goals at once it is suggested to improve the PV models in ESP-r, taking into account all phenomena affecting the power output of PV modules: solar radiation intensity, cell temperature, angle of incidence, spectral distribution, uncertainty in manufacturer's ratings, ageing, mismatch, soil and dirt, snow, partial shading, diodes and wiring. This would provide a more realistic estimate of the probable output of the PV system over its lifetime. It is suggested to implement three models: a simple model based on constant efficiency, a one-diode equivalent model with explicit temperature dependency of the parameters, and the Sandia model for cases when detailed modeling is required.
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A simulation of shading effects in arrays with different string configurations has been done. Simulation has been performed using as the basic unit the solar cell, modelled in direct bias by the conventional one exponential model, and in reverse bias by an equation previously validated in different types of photovoltaic cells reverse characteristics. The influence of the amount of shading, the type of reverse characteristic of the cell, the string length and the number of shaded cells has been analysed, and some recommendations are extracted.
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In this contribution a simulation procedure is described which was developed as a working tool to calculate the energy output of building-integrated photovoltaic (PV) arrays experiencing shading or reflection effects. A three-quadrant solar cell model incorporating the reverse bias characteristics and breakdown voltage is verified by current-voltage (I–V) measurements performed on commercially manufactured mc-Si solar cells under controlled laboratory conditions. For the simulations, a point matrix giving the irradiation distribution over the PV array is calculated for each hour using a raytracing technique. With a raytracing technique, shading of both beam and diffuse irradiation as well as primary and secondary reflections can be modelled. The results of two cases studies simulated using this technique are presented and analysed. In conclusion, general guidelines based on the simulation results are drawn up. These guidelines aim to assist architects and engineers in planning an optimized layout strategy of building-integrated PV arrays to reduce energy losses caused by shading.
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Solar photovoltaic (PV) arrays in field conditions deliver lower power than the array rating. In this paper, the sensitivity of solar cell parameters in the variation of available power from the array is investigated. The parameters characteristic of aging and fresh cells used in prototype field systems have been used for computation of reduction in the available power. It is found that in series string the fractional power loss would increase from 2% to 12% with aging of solar cells. However, this fractional power loss may be reduced to 0.4–2.4% by an appropriate series-paralleling.
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Quality inspection of PV-modules includes measurement of peak-power Ppk and internal series resistance Rs. Peak-power is defined as maximum power under standard test conditions (STC). As the peak-power can decrease due to degradation effects, a continuous quality inspection has to be realized on-site under natural ambient conditions. Losses in the PV-modules can be described by an internal series resistance Rs. An increasing Rs shows internal losses as well as degrading contacts. A measuring method is presented, which can measure under natural ambient conditions and directly display the results peak-power Ppk and internal series resistance Rs. I-V-characteristics measured under ambient conditions can be corrected concerning temperature and irradiation according to IEC 60891. The description of the characteristic by the "effective solar cell characteristic" makes it possible to explicitely carry out the calculations for Ppk. IEC 60891 also describes a method for the evaluation of the internal series resistance Rs. A graphic method is used in order to determin certain points in the I-V-characteristic, which serve as input-values for the calculation of the series resistance. The accuracy of this graphic method is limited by the accuracy of the graphically determined points. Using the method of the "effective solar cell characteristic" it is possible to explicitely calculate the demanded points of the I-V-characteristic, thus beeing capable of explicit calculation of the series resistance Rs. The method of the "effective solar cell characteristic" is presented as well as some significant results concerning Ppk– and Rs–measurement under natural ambient conditions.
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A new method for estimating the irradiance on a partially shaded photovoltaic generator system is proposed. The basic principle of this method consists of two parts: firstly, an approximation of the obstacles’ outline or the local horizon by a set of linear functions. Here, a survey of the surroundings is based on the reading of the topographic coordinates of the only significant points of all the objects surrounding the photovoltaic generator. Secondly, the irradiance on the photovoltaic plane is estimated using an accurate model such as the Perez et al. model and assuming that the shading affects both the direct radiation and a part of the diffuse component (circumsolar component).The aim of this paper is to present the principles of the proposed method and the algorithm used for calculating the irradiance on shaded planes. In addition, the results of the comparison between the simulated and measured values of this method are presented.
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Partial shadowing has been identified as a main cause for reducing energy yield of grid-connected photovoltaic systems. The impact of the applied system configuration on the energy yield of partially shadowed arrays has been widely discussed. Nevertheless, there is still much confusion especially regarding the optimal grade of modularity for such systems. A 5-kWp photovoltaic system was installed at K.U. Leuven. The system consists of three independent subsystems: central inverter, string inverter, and a number of AC modules. Throughout the year, parts of the photovoltaic array are shadowed by vegetation and other surrounding obstacles. The dimensions of shadowing obstacles were recorded and the expectable shadowing losses were estimated by applying different approaches. Based on the results of almost 2 years of analytical monitoring, the photovoltaic system is assessed with regard to shadowing losses and their dependence on the chosen system configuration. The results indicate that with obstacles of irregular shape being close to the photovoltaic array, simulation estimates the shadowing losses rather imprecise. At array positions mainly suffering from a reduction of the visible horizon by obstacles far away from the photovoltaic array, a simulation returns good results. Significant differences regarding shadow tolerance of different inverter types or overproportional losses with long module strings could not be confirmed for the system under examination. The negative impact of partial shadowing on the array performance should not be underestimated, but it affects modular systems as well as central inverter systems.
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The aim of this study is to investigate the effects of non-uniform solar irradiation distribution on energy output of different interconnected configurations in photovoltaic (PV) arrays. In order to find which configuration is less susceptible to mismatch effects, a PV module model is developed. This model can take into consideration the effects of bypass diodes and the variation of the equivalent circuit parameters with respect to operating conditions. The proposed model can provide sufficient degree of precision as well as solar cell-based analysis in analyzing large scale PV arrays without increasing the computational effort. In order to produce more reliable and robust simulations, improved and extended algorithms are presented. Some results are discussed in detail and some recommendations are extracted by testing several shading scenarios.
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Partially shaded photovoltaic (PV) modules typically exhibit additional difficulties in tracking the maximum power point since their power–voltage characteristics are complex and may have multiple local maxima. For this reason, conventional techniques fail to track the maximum power point effectively if the PV array is partially shaded or some of its cells are damaged. This paper presents a novel power compensation system for PV arrays for complicated non-uniform insolation conditions. The proposed system is based on recovering the power of non-shaded PV modules into the system again completely by forward biasing a bypass diode of the shaded PV modules. For this purpose, the proposed system uses dc–dc converters equipped with each PV string in the PV array. For identifying which shaded PV modules should be deactivated, the operating voltage of the PV modules are monitored and compared. The proposed system enables the non-shaded PV modules to operate effectively at their normal maximum power point. The effectiveness of the proposed system is investigated and confirmed for complicated partially shaded PV arrays.
Review and recommendations for improving the modeling of building integrated photovoltaic systems. In: Building simulation, ninth international IBPSA conference, vols. 15-18. Montréal Canada
  • D Thevenard
Thevenard D. Review and recommendations for improving the modeling of building integrated photovoltaic systems. In: Building simulation, ninth international IBPSA conference, vols. 15-18. Montréal Canada; August 2005. p. 1221-8.