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.     

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.     

Effects of mismatch losses in photovoltaic arrays

Experimental and modeling results on the effects of mismatch losses in photovoltaic arrays are presented. Field tests conducted on each of the 192 modules are used to describe the variation in the properties of production run photovoltaic modules. Module specific estimates of a five-parameter module model are obtained by nonlinear regression. Mathematical models of four-module parallel string and series block photovoltaic array performance based on the five-parameter module model are developed and used to evaluate the variation in maximum output power and mismatch loss of arrays with random module orderings. Module maximum output power averaged 14% below the nameplate rating and exhibited a coefficient of variation of 2.1%. Mismatch losses were very small, never exceeding 0.53%. No differences between parallel string and series block arrays in array maximum output power were observed.     

Energy yield simulations of interconnected solar PV arrays

In this paper, the electrical characteristics of array interconnection schemes are investigated using simulation models to find a configuration that is comparatively less susceptible to shadow problem and power degradation resulting from the aging of solar cells. Three configurations have been selected for comparison: (i) simple series-parallel (SP) array which has zero interconnection redundancy; (ii) total-cross-tied (TCT) array which is obtained from the simple SP array by connecting ties across each row of junctions; it may be characterized as the scheme with the highest possible redundancy; and (iii) 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.     

大型地面光伏电站中光伏方阵容量的优化设计

随着光伏组件光电转换效率的提高,以及逆变器单机功率的增大,大型地面光伏电站中光伏方阵容量也从1 MW、1.6 MW、2.5 MW逐渐增大到3.125 MW.以新疆维吾尔自治区吐鲁番地区的气候条件为例,对在该地区建设的大型地面光伏电站中光伏方阵容量分别选择3.125 MW和6.25 MW时的经济性及可行性进行了分析.结果...     

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...     

串并联太阳能电池弧形光伏组件的发电性能研究

将弧形光伏组件安装在建筑和汽车上获取电能,已受到人们越来越多的关注。为获得更高的输出功率,有必要研究由互连太阳能电池组成的、电流不匹配的弧形光伏组件的特性。研究重点关注由串并联太阳能电池组成的弧形光伏组件的发电性能,设计了不同曲率的非平面微型光伏模块,并通过测量获取光伏模块的参数。与平面光伏模块相比,弧形光伏模块的发电量较小。此外,利用二极管模型分析了光伏模块的特性,说明并联比串联功率高的原因。最后研究了实际应用中太阳能电池的互连问题。结果表明,在理想模型下并联能获取更多电能,但大尺寸的光伏模块会产生更大电流,可能会在实际运行中产生额外损耗。因此,在实际应用中设计弧形光伏组件时也应考虑太阳能电池的互连。     

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.     

光伏组件在非标准测试条件下的能量分布

该研究基于非标准测试条件,结合五参数电学模型、热阻模型和损失模型,提出一种评估光伏组件能量分布的耦合模型.通过模拟数据和实验数据的对比,验证该模型在模拟光伏组件发电量和太阳电池温度方面的准确性,并研究非标准测试条件下光伏组件的运行状态和能量分布情况.结果表明,在某个晴天下,对于一个实际运行的光伏组件,21.9％的入射太...     

灰尘导致的光伏电站发电损失的对比实验

对地面光伏电站的2个采取不同清洁策略方阵的运行数据和辐照数据分成上午数据和下午数据,分别进行处理和分析.介绍去除数据集中的异常数据和不可信数据的预处理的方法.之后,对比组串的发电数据,发现了2个方阵中发电异常的2个组串.为了研究清洁增益的效果,计算不同太阳辐照度下2个方阵的功率比值.发现对于不同的辐照度,清洁增益的效果...     

Modeling the photovoltaic potential of a site

Measurements of the power produced by a photovoltaic (PV) system are important for technical as well as financial reasons, especially in large installations. The energy produced by a PV system is modeled through its nominal power, the incoming irradiance and the major energy loss mechanisms. These mechanisms involve the temperature of the cells, the response of a cell to low intensity light, the spectrum and polarization of the light, the deviation from maximum power point tracking, module mismatch and ohmic losses. The experimental quantities needed by the model are the solar irradiance at the plane of the array, the cell temperature and the nominal power of the system. In this work, we present part of the results of the theoretical calculations and their comparison with actual experimental measurements.     

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.     

The risk of power loss in crystalline silicon based photovoltaic modules due to micro-cracks

Micro-cracks in wafer based silicon solar cell modules are nowadays identified by a human observer with the electroluminescence (EL) method. However, the essential question of how the micro-cracks affect the PV module performance has yet to be answered. We experimentally analyze the direct impact of micro-cracks on the module power and the consequences after artificial aging. We show that the immediate effect of micro-cracks on the module power is small, whereas the presence of micro-cracks is potentially crucial for the performance of the module after artificial ageing. This confirms the necessity to develop the means of quantifying the risk of power loss in PV modules with cracked solar cells in their lifetime, in order to enable manufacturers to discard defective modules with high risk of failure while keeping modules with uncritical micro-cracks. As a first step towards risk estimation we develop an upper bound for the potential power loss of PV modules due to micro-cracks in the solar cells. This is done by simulating the impact of inactive solar cell fragments on the power of a common PV module type and PV array. We show that the largest inactive cell area of a double string protected by a bypass diode is most relevant for the power loss of the PV module. A solar cell with micro-cracks, which separate a part of less than 8% of the cell area, results in no power loss in a PV module or a PV module array for all practical cases. In between approximately 12 and 50% of inactive area of a single cell in the PV module the power loss increases nearly linearly from zero to the power of one double string.     

光伏发电功率预测预报系统V2.5在东洞滩光伏电站的安装及运行

对光伏并网电站的产能加以预测和科学化管理,能够提高电网消纳光伏发电出力的能力及电站的运营水平。以甘肃省酒泉市东洞滩光伏电站为例,介绍了光伏发电功率预测预报系统V2.5在该光伏电站的安装、调试及运行情况,阐明了系统的安装环境、实况功率采集、预报结果上报等,并针对实况功率采集,分析了104传输规约的报文结构及通讯过程,最后给出了系统的调试和维护方案。运行结果表明,该系统运行稳定,预报效果良好,对电网调度和光伏电站的经济运行具有较好的指导意义。     

Reliability evaluation of solar photovoltaic arrays

The operational lifetime of large solar PV arrays is investigated using the probability theory for the assessment of reliability. Arrays based on the following three solar cell interconnection schemes have been considered: (i) simple series-parallel (SP) array, (ii) the total-crossed-tied (TCT) array which is obtained from the SP array by connecting ties across each row of junctions and (iii) the bridge-linked (BL) array in which all cells are interconnected in bridge rectifier fashion. To evaluate the reliability of the bridge-linked configuration, the cut-set technique is used. Computational results based on arrays consisting of (720×20) solar cells indicate that the operational life of an array is almost doubled by the introduction of cross ties (TCT or BL schemes) in the array. The operational lifetime can be further increased by 30% by modularized networks based on TCT and BL configurations. These results are based on a theoretical analysis, however, and not on measured efficiency and life expectancy of solar cells.     

Monte Carlo techniques to analyse the electrical mismatch losses in large-scale photovoltaic generators

In large-scale photovoltaic generators, the arrangement of modules with different electrical characteristics could involve a considerable mismatch between the single components resulting in a power loss. This means the actual power is less than the sum of the maximum output powers of the individual PV modules, operating at same irradiance-temperature conditions. To reduce the mismatch losses and to calculate it under operating conditions, a statistical approach based on Monte Carlo simulation techniques, has been developed and validated. The simulation model shows that it is possible to meet the required mismatch level, with a random arrangement, starting from a modules population characterized in terms of short circuit current, I_sc and open circuit voltage V_oc, by a probability density function with a imposed variance. The method has been successfully applied for a 100 kWp standard unit photovoltaic generator, the computational results have shown good agreement with the experimental data.     

A SIMPLIFIED METHOD FOR DETERMINING THE AVAILABLE POWER AND ENERGY OF A PHOTOVOLTAIC ARRAY

A practical method of calculating the power and energy capabilities of a PV array source is presented in this paper. The method is based on power flow relationships with average values for constants and actural measurements of key variables, solar irradiance and module temperature on an hourly basis or other discrete time intervals. Included in this paper is an example for a PV plant and a simple procedure for constructing and validating the math model

The method is applicable to any PV array configuration which is operating normally, i.e., when no PV modules are bypassed by the shunt diodes. The array can comprise one or more PV modules. The accuracy of this method is dependent upon proper selection of the values of various constants in the math model as well as how well the model has been validated. The calculation and display of maximum power capability in real-time have been implemented in several PV plants. Some of them have found it to be very useful for operation, maintenance, performance analysis, and energy utilization improvement purposes.     

Fuzzy logic-based MPPT controllers for three-phase grid-connected inverters

In photovoltaic (PV) applications, a maximum power point tracking (MPPT) module is necessary to extract the whole energy that the PV module can generate depending on the instantaneous conditions of the PV system. A PV module is obtained by connecting a number of solar cells in series and parallel, which causes voltage and current to increase at module terminations. The present work is based on a three-phase grid-connected inverter designed for a 100 kW PV power plant that uses an MPPT scheme based on fuzzy logic controllers. The whole system presented is simulated in MATLAB. The fuzzy logic-based MPPT controllers show accurate and fast responses and are integrated into the inverter, so that the there is no requirement for a dc–dc converter. The inverter allows full control of reactive power.     

Techno-economic analysis and modelling of a remote photovoltaic water pumping system in the desert of Tunisia

For estimating the performance of a photovoltaic (PV) water pumping system without battery storage, a simple algorithm has been developed. This simulation program uses the hourly global solar radiation, the hourly ambient temperature and the hourly wind speed as the input, moreover the characteristics of region (latitude, longitude, ground albedo) and characteristics of PV water pumping system (orientation, inclination, nominal PV module efficiency, NOCT, PV array area, PV temperature coefficient, miscellaneous power conditioning losses, miscellaneous PV array losses, temperature of reference, moto-pump efficiency and inverter efficiency). This work allows evaluating the economic interest of a remote PV water pumping systems in the desert of Southern Tunisia, which will have to satisfy an average daily volume of 45 m³ throughout the year compared to another very widespread energy system in the area, the diesel genset (DG), by using the method of the life-cycle cost (LCC). The cost per m³ of water was calculated for this system. It is found that the LCC for PV system is 0.500 TND/m³ and the LCC DG is 0.837 TND/m³. The present study indicates economic viability of PV water pumping systems in the desert of Tunisia.     

Performance of Silicon Heterojunction Photovoltaic modules in Qatar climatic conditions

We report on the performance of two cell technologies: Silicon Heterojunction (SHJ) and conventional diffused junction n-type mono-crystalline silicon Photovoltaic (PV) arrays, under a harsh environment condition with high temperature and dust accumulation, typical to Qatar. A comparison of the energy yield and Performance Ratio (PR) at plane of array global irradiance as well as module temperature (T_mod) of the two technologies is presented. The SHJ arrays showed a higher energy yield as compared with the conventional arrays thanks to the higher efficiency of the SHJ. The results showed also that dust accumulated on PV modules may cause a drop in the PR of up to approximately 15% if the module is not cleaned for one month. Scheduled module cleaning or raining will return the PR close to its initial value.