A virtual reality study of surrounding obstacles on BIPV systems for estimation of long-term performance of partially shaded PV arrays

This work presents a new analytical method to evaluate the efficiency of PV systems working in partial shading conditions by taking into account the effect of surrounding obstacles. A mathematical procedure to determine the shadowed area on PV modules, depending on the location of the PV system and obstacles nearby the array has been implemented. This methodology allows the study of the power losses present in the PV systems due to partial shading conditions as well as its effect on the evolution of the maximum power point of the array. The application of this methodology on the behavior of three PV systems located in different cities of Turkey, such as Istanbul, Izmir, and Antalya, working under the same conditions of obstacle surrounding, along a year is presented.     

Performance enhancement of partially shaded solar PV array using novel shade dispersion technique

Solar photo voltaic array (SPVA) generates a smaller amount of power than the standard rating of the panel due to the partial shading effect. Since the modules of the arrays receive different solar irradiations, the P-V characteristics of photovoltaic (PV) arrays contain multiple peaks or local peaks. This paper presents an innovative method (magic square) in order to increase the generated power by configuring the modules of a shaded photovoltaic array. In this approach, the physical location of the modules in the total cross tied (TCT) connected in the solar PV array is rearranged based on the magic square arrangement pattern. This connection is done without altering any electrical configurations of the modules in the PV array. This method can distribute the shading effect over the entire PVarray, without concentrating on any row of modules and can achieve global peaks. For different types of shading patterns, the output power of the solar PV array with the proposed magic square configuration is compared with the traditional configurations and the performance is calculated. This paper presents a new reconfiguration technique for solar PV arrays, which increases the PV power under different shading conditions. The proposed technique facilitates the distribution of the effect of shading over the entire array, thereby, reducing the mismatch losses caused by partial shading. The theoretical calculations are tested through simulations in Matlab/ Simulink to validate the results. A comparison of power loss for different types of topologies under different types of shading patterns for a 4×4 array is also explained.     

Forecasting photovoltaic array power production subject to mismatch losses

The development of photovoltaic (PV) energy throughout the world this last decade has brought to light the presence of module mismatch losses in most PV applications. Such power losses, mainly occasioned by partial shading of arrays and differences in PV modules, can be reduced by changing module interconnections of a solar array. This paper presents a novel method to forecast existing PV array production in diverse environmental conditions. In this approach, field measurement data is used to identify module parameters once and for all. The proposed method simulates PV arrays with adaptable module interconnection schemes in order to reduce mismatch losses. The model has been validated by experimental results taken on a 2.2 kW_p plant, with three different interconnection schemes, which show reliable power production forecast precision in both partially shaded and normal operating conditions. Field measurements show interest in using alternative plant configurations in PV systems for decreasing module mismatch losses.     

Low light conditions modelling for building integrated photovoltaic (BIPV) systems

The low irradiance efficiency of photovoltaic modules is important to the optimization of BIPV systems. When photovoltaic modules are integrated into a building, architectural design considerations compete with maximizing photovoltaic energy production. As a result, BIPV arrays are often not facing south and are frequently mounted vertically. Under these conditions, a greater portion of the total sunlight striking the array is diffuse or at high angles of incidence. In northern latitudes a significant amount of the total yearly energy is produced at low light levels.A grid-connected array of BIPV modules integrated into the BCIT Technology Centre building in Burnaby, B.C. was used for assessing the accuracy of an energy performance model developed for BIPV systems. The BIPV system uses AC modules and a computerized data acquisition system for monitoring the performance of modules and inverters. The performance model was developed from analysis of the open circuit voltage, maximum power point voltage and maximum power point current of the individual modules comprising the BIPV array.The algorithm for calculating power output of the photovoltaic array is derived from the ideal diode equation using the single diode model of a photovoltaic cell. An empirically derived parameter modifies the equation. Once the parameters for different module technologies are established, it is possible to compare their annual performance in a BIPV system.     

Optimal Su-Do-Ku based interconnection scheme for increased power output from PV array under partial shading conditions

Partial shading is a common phenomenon in PV arrays. They drastically reduce the power output because of mismatch losses, which are reliant on the shape of the shade as well as the locations of shaded panels in the array. The power output can be improved by distributing the shade over various rows to maximize the current entering the node. A Su-Do-Ku configuration can be used to rearrange the physical locations of the PV modules in a total cross tied PV array with the electrical connections left unchanged. However, this arrangement increases the length of the wire required to interconnect the panels thus increasing the line losses. In this paper, an improved Su-Do-Ku arrangement that reduces the length of the wire required for the connection is proposed. The system is designed and simulated in a Matlab/Simulink environment for various shading patterns and the efficacies of various arrangements are compared. The results prove that the power output is higher in the proposed improved Su-Do-Ku reconfiguration technique compared to the earlier proposed Su-Do-Ku technique.     

Positioning of PV panels for reduction in line losses and mismatch losses in PV array

Partial shading decreases the power output of PV arrays due to mismatch losses. These losses are dependent on the shading pattern and the relative positions of shaded modules in the array. Various static and dynamic reconfiguration techniques have earlier been proposed to mitigate these losses. In an earlier proposed static reconfiguration technique, the power generation is enhanced by altering the physical location of the PV panels using a random Sudoku configuration without modifying the TCT (Total-Cross-Tied) based electrical connections. However, this arrangement faces drawbacks due to ineffective dispersion of shade and significant increase in wiring required. In this work, an optimal Sudoku arrangement to overcome these drawbacks is formulated. Further analysis indicate that the global peak of the optimal Sudoku based PV array occurs as the right most peak in the curve for most shading conditions, thus evidently obviating the need for complex MPPT (Maximum-Power-Point-Tracking) algorithms. The proposed configuration is compared with various other existing reconfiguration schemes in terms of power output and the comparison is presented. In addition, a general formulation is proposed to expand this pattern to any generic array. A strategy is also proposed to make such an interconnection practicable for very large size PV arrays.     

Impact of uneven shading and bypass diodes on energy extraction characteristics of solar photovoltaic modules and arrays

Solar photovoltaic (PV) energy is becoming an increasingly important part of the world's renewable energy. In order for effective energy extraction from a solar PV system, this paper investigates I–V and P–V characteristics of solar PV modules and arrays. The paper particularly focuses on I–V and P–V characteristics of PV modules and arrays under uneven shading conditions, and considers both the physics and electrical characteristics of a solar PV system in the model development. The article examines how different bypass diode arrangements could affect maximum power extraction characteristics of a solar PV module or array. It is found in this article that under uneven shading conditions, solar PV cells may perform in very different ways and a solar PV system may exhibit multiple peaks in its P–V characteristics. The study of this article also shows that the arrangement of largely distributed bypass diodes within a PV module could effectively improve efficiency and maximum power point tracking strategies for energy conversion of solar PV systems.     

基于S-V特性分析的晶硅光伏组件阴影遮障诊断

针对广泛使用的晶硅光伏组件,通过Simulink建立太阳电池双二极管精确仿真模型,对实际应用中最常见的光伏组件阴影遮挡故障进行多种工况的仿真验证。根据I-V曲线拐点、台阶、曲线下积分面积（S）下降的特征,提出一种基于S-V曲线特性的光伏组件阴影遮挡故障的在线诊断方法。该方法建立S-V曲线,根据S-V曲线分叉点位置可判断光伏组件遮挡情况,通过整体积分面积进而判断遮挡比例。对温度、辐照度进行折算,使该方法在全工况下适用。结合光伏组件功率优化器验证该诊断方法有较高的准确率,并且可准确地判断阴影遮挡面积,具有很高的实际应用价值。     

Practical application of building integrated photovoltaic (BIPV) system using transparent amorphous silicon thin-film PV module

An analysis has been carried out on the first practical application in Korea of the design and installation of building integrated photovoltaic (BIPV) modules on the windows covering the front side of a building by using transparent thin-film amorphous silicon solar cells. This analysis was performed through long-term monitoring of performance for 2 years. Electrical energy generation per unit power output was estimated through the 2 year monitoring of an actual BIPV system, which were 48.4 kWh/kWp/month and 580.5 kWh/kWp/year, respectively, while the measured energy generation data in this study were almost half of that reported from the existing data which were derived by general amorphous thin-film solar cell application. The reason is that the azimuth of the tested BIPV system in this study was inclined to 50° in the southwest and moreover, the self-shade caused by the projected building mass resulted in the further reduction of energy generation efficiency. From simulating influencing factors such as azimuth and shading, the measured energy generation efficiency in the tested condition can be improved up to 47% by changing the building location in terms of azimuth and shading, thus allowing better solar radiation for the PV module. Thus, from the real application of the BIPV system, the installation of a PV module associated with azimuth and shading can be said to be the essentially influencing factors on PV performance, and both factors can be useful design parameters in order to optimize a PV system for an architectural BIPV application.     

基于图像处理的光伏局部阴影区域分割方法

为解决真实场景中光伏组件局部阴影区域分割受环境干扰的问题,该文提出基于图像处理的光伏局部阴影区域分割方法。根据光伏组件特征用改进的阈值分割方法提取组件边框,采用Hough变换检测组件边框线段,计算包围边框线段端点的最小凸包作为感兴趣区域。在感兴趣区域内再次使用改进的阈值分割方法提取局部阴影区域。用模拟仿真图像和真实场景图像验证该文所提方法的有效性,实验结果表明：所提方法可准确分割出光伏组件上的局部阴影区域且保持了遮挡区域的细节信息。与多阈值分割方法和基于Canny边缘检测的分割方法相比,该文所提方法的错误分类误差更小,类别像素准确率更高。     

Environmental payback time analysis of a roof-mounted building-integrated photovoltaic (BIPV) system in Hong Kong

This paper reports the investigation results of the energy payback time (EPBT) and greenhouse-gas payback time (GPBT) of a rooftop BIPV system (grid-connected) in Hong Kong to measure its sustainability. The 22 kWp PV array is facing south with inclined angle of 22.5°. The hourly solar irradiance and ambient air temperature from 1996 to 2000 were used as weather data input. The annual power output was found to be 28,154 kWh. The embodied energy for the whole system in the lifespan was 205,816 kWh, including 71% from PV modules and 29% from balance of system (BOS). The percentage of embodied energy for silicon purification and processing reached 46%. The EPBT of the PV system was 7.3 years, and the GPBT was estimated to be 5.2 years considering fuel mixture composition of local power stations. This paper also discussed the EPBTs for different orientations, ranging from 7.1 years (optimal orientation) to 20.0 years (west-facing vertical PV façade). The results show that the ‘sustainability’ of a PV system is affected by its installation orientation and location. Choosing locations and orientations with higher incident solar irradiance is one key for the sustainability of BIPV technology applications.     

Artificial neural network-polar coordinated fuzzy controller based maximum power point tracking control under partially shaded conditions

The one of main causes of reducing energy yield of photovoltaic systems is partially shaded conditions. Although the conventional maximum power point tracking (MPPT) control algorithms operate well under uniform insolation, they do not operate well in non-uniform insolation. The non-uniform conditions cause multiple local maximum power points on the power?voltage curve. The conventional MPPT methods cannot distinguish between the global and local peaks. Since the global maximum power point (MPP) may change within a large voltage window and also its position depends on shading patterns, it is very difficult to recognise the global operating point under partially shaded conditions. In this paper, a novel MPPT system is proposed for partially shaded PV array using artificial neural network (ANN) and fuzzy logic with polar information controller. The ANN with three layer feed-forward is trained once for several partially shaded conditions to determine the global MPP voltage. The fuzzy logic with polar information controller uses the global MPP voltage as a reference voltage to generate the required control signal for the power converter. Another objective of this study is to determine the estimated maximum power and energy generation of PV system through the same ANN structure. The effectiveness of the proposed method is demonstrated under the experimental real-time simulation technique based dSPACE real-time interface system for different interconnected PV arrays such as series-parallel, bridge link and total cross tied configurations.     

阴影遮挡下光伏组件横竖向放置对发电量的影响

为了提高阴影遮挡时光伏组件的发电量,针对横、竖向放置时光伏组件相互遮挡产生的功率损失,建立了光伏组件在阴影遮挡情况下的数学模型,考虑了光伏组件并联旁路二极管的影响,仿真模拟了阴影遮挡下横、竖向放置时光伏组件的输出特性,进而以某地100kW光伏阵列为例,计算了光伏组件在不同摆放方式、不同倾角与间距下的辐射量、年发电量、阴影损失及年平均效率,为光伏电站的初步设计提供了一定的参考价值。     

基于并联光伏组件外特性的最大功率点跟踪方法

当阴影条件变化时,并联光伏组件的全局最大功率点(MPP)会随之改变.为了实现太阳能发电最大化,要求最大功率点跟踪(MPPT)方法始终能实时而准确地锁定住并联光伏组件的全局MPP.不同阴影条件下并联光伏组件会呈现不同的外特性特征,如多阶梯的电流电压特性以及多峰值的功率电压特性.基于此现象,该文提出一种基于并联光伏组件外特...     

光伏电站中光伏组件串联数的新设计思路

在对光伏电站的光伏方阵进行设计时,行业内大部分设计人员在计算光伏组件串联数时往往会忽略"光伏组件工作条件下的极限温度"与"气象极限温度"二者的区别,习惯上采用气象极限温度来计算光伏组件串联数.通过分析光伏组件工作条件下的极限温度与气象极限温度的区别,指出了常规计算时采用气象极限温度取值存在的问题,拓宽了看待光伏组件工作...     

Self-shading losses of fixed free-standing PV arrays

The energy yield of a photovoltaic (PV) system with fixed free-standing PV arrays is affected also by the self-shading effects. The rows of PV modules in arrays may partially shade the PV modules in the rows behind. In this paper the effects of the row distance on the PV system’s energy yield are evaluated. The estimation of the self-shading losses by the irradiation losses simply overestimates the losses; therefore we developed a simulation model to simulate the real energy loss due to shading of the preceding row in a PV system. The model demonstrates that the self-shading energy losses are at commonly used distances between rows from 20 to 40% lower than the irradiation losses at the modules’ bottom considering the shading conditions. The self-shading energy loss is studied in the case of Ljubljana, Slovenia which may refer to the whole Central Europe. To estimate the self-shading losses a technology-and with parameter modifications also location-independent empirical equation based on module-to-cell width ratio was derived and validated.     

Analysis of thermal and electrical performance of semi-transparent photovoltaic (PV) module

Building-integrated PhotoVoltaic (BIPV) is one of the most fascinating PV application technologies these days. To apply PV modules in buildings, various factors should be considered, such as the installation angle and orientation of PV module, shading, and temperature. The temperature of PV modules that are attached to building surfaces especially is one of the most important factors, as it affects both the electrical efficiency of a PV module and the energy load in a building. This study investigates the electrical and thermal performance of a semi-transparent PV module that was designed as a glazing component. The study evaluates the effects of the PV module's thermal characteristics on its electrical generation performance. The experiment was performed under both Standard Test Condition (STC) and outdoor conditions. The results showed that the power decreased about 0.48% (in STC with the exception of the temperature condition) and 0.52%(in outdoor conditions, under 500 W/m²) per the 1 °C increase of the PV module temperature. It was also found that the property of the glass used for the module affected the PV module temperature followed by its electrical performance.     

Experimental results of controlled PV module for building integrated PV systems

Last issues about Building Integrated Photovoltaic Systems (BIPV) still show average Performance Ratio (PR) values in the range of 0.75–0.80. The main causes well known: partial shadows, temperature effects, PV inverter losses, thermal losses, etc. and mismatching losses. Ideally, all the modules work in the same conditions, but differences between modules really exist due to differences in the working temperature, the inclination or orientation angles, differences in the I–V characteristic coming from the manufacturing process, etc. The effect is that the output power of the complete PV system is lower than the addition of the power of each PV module.These mismatching losses can be decreased by means of suitable electronics. This paper presents the experimental results obtained over PV systems equipped with controlled PV modules, PV modules with low cost and high efficiency DC–DC converters, including MPPT algorithm and other functions, such as power control and Power Line Communications (PLC).Tests have been divided into two great categories: tests on the electronic performance of the DC–DC converter and tests on grid-connected PV systems with multiple DC–DC converters. Many of these tests have been carried out taking advantage of the PV System Test Platform, a powerful tool especially designed by Robotiker to evaluate all kind of PV systems, especially systems with differences between modules. Aspects of the DC–DC converter performance have been detailed and among the most important experiments, the paper analyses different situations such as partial shadows, different inclined planes, PV systems with different PV modules, and finally a comparison between a conventional system and a system composed by controlled PV modules have been described. To sum up, the importance of a good system dimensioning is analysed, with very interesting results.     

局部阴影下光伏阵列全局MPPT控制方法

在局部阴影条件下,由带旁路二极管光伏组件构成的光伏阵列的功率-电压特性曲线可能有多个局部最大功率点。为保证寻找到光伏阵列的全局最大功率点,提出了一种基于扰动观测法和导纳增量法的改进全局最大功率点跟踪的控制方法。通过建立仿真模型和试验,验证了该方法的有效性。与基于普通扰动观测法的控制策略比较分析表明,改进算法具有更好的跟踪效果与更小的功率振荡损失。     

An investigation on partial shading of PV modules with different connection configurations of PV cells

Partial shading is a commonly encountered issue in a PV (photovoltaic) system. In this paper, five different connection configurations of PV cells are studied to compare their performance under the condition of partial shading. They are SS (simple series), SP (series-parallel), TCT (total-cross-tied), BL (bridge-linked) and HC (honey comb) configurations. The electric network of each connection configuration is analyzed, taking into account the nonlinear nature of PV cells, by writing the Kirchhoff’s voltage and current equations. The analysis is followed by solving the simultaneous nonlinear equations using the Newton-Raphson algorithm, which allows the I-V (current-voltage) characteristic of the module with a specific configuration in response to different types and levels of partial shading to be evaluated. Comparison of the maximum power and fill factors of the five connection configurations is then carried out. Also studied is the reverse voltage across each PV cell. It is found that in most cases, the TCT configuration has a superior performance over the other four configurations in most comparison indices.