灰尘对光伏发电的影响及组件清洗研究

在大型光伏电站运行发电过程中,灰尘对其发电量的影响不容忽视。本文从灰尘的来源、种类及特性出发进行分析,结合国内外光伏电站组件清洗相关实测数据,研究灰尘对光伏发电的影响;并在此基础上,总结、对比目前已有的光伏电站组件清洗方式,分析各种清洗方式的选择方法和清洗周期的判断,旨在探索研究光伏组件清洗的最佳方案。     

阴影遮蔽条件下光伏发电效率的增大方法

受阴影遮蔽影响,光伏阵列输出功率下降,功率曲线呈现多峰值,使传统的最大功率点(MPPT)算法失效陷入局部极值点。基于光伏电池的等效电路模型,在正常和有阴影遮蔽情况下对光伏组件串并联输出特性进行仿真,分析功率曲线上局部极值点的产生原因及变化规律。针对阴影遮蔽对光伏发电效率的影响,提出建立微型光伏发电系统,采用光伏组件间解耦的方法,跟踪每个光伏组件的最大功率点,使光伏发电效率达到最优。试验结果验证了该方法的可行性,为今后光伏电站的建设提供了指导。     

光伏组件表面积灰对其发电性能的影响

利用计算机模拟的方法对有灰尘沉积的光伏组件输出性能进行研究,采用MATLAB／SIMULINK模拟灰尘沉积对光伏组件输出性能的影响,得到不同灰尘沉积情况下的光伏组件的输出特性曲线,由特性曲线可以看出,随着灰尘沉积的增多,最大功率点功率下降明显。在理论研究的基础上,搭建实验平台进行实验研究,结果证明仿真结果是有效可信的。     

山地光伏电站光伏组件阴影遮挡技改方案的经济性分析

针对山地光伏电站光伏组件阴影遮挡问题,提出了重接线、调整光伏支架立柱高度或光伏组件安装倾角、以大换小、拆除重装4种方案,并针对每种方案进行经济性分析,给出不同新增投资下,投资回收期为5年时,需要提升的等效利用小时数。分析结果显示：当上网电价为1.0元/kWh时,在严格控制成本的情况下,老旧山地光伏电站采用重接线、调整光伏支架立柱高度或光伏组件安装倾角这两种方案可能在5年内回收成本;而对于“以大换小”方案,若容配比为1.3:1.0,单瓦静态投资从0.9元/W增至1.3元/W(扣除了光伏组件回收资金)时,年等效利用小时数需提升约235.8～369.2 h,发电量提升16.8%～26.4%,才能实现投资回收期5年的目标;拆除重建方案在经济性上基本不可行。该研究旨在为有技改需求的电站提供数据参考。     

光伏组件对阴影敏感度的测试及分析应用

针对光伏电站组件的布置方式,给出光伏组件防反二极管连接方式的测试方法,并应用于平整度不同的场地及不同布置类型的组件。利用专业测试设备,对组件上不同方位阴影遮挡的敏感度进行了现场试验及分析。分析结果表明,防反二极管连接方式是影响光伏组件对阴影敏感度的决定性因素。当防反二极管为竖向布置的情况下,场地南北高差为主要影响时,建议组件横向放置;当场地东西高差为主要影响时,建议组件竖向放置。     

积灰对光伏发电的影响及除尘效果实验研究

通过对兰州地区的灰尘沉降情况及积灰影响光伏组件发电效率进行实验研究,结果表明,在秋季无降雨情况下,当积灰密度达到2.068 g/m2时,输出电流下降约22.6%,平均每天下降1.51%。同时以某地38 kW分布式光伏电站为背景,分析水射流清洗方式的清灰效益及除尘率,发现清洗后除尘率可达86.3%,平均每天可多发电6.25 kWh。并对课题组自行研制的光伏电站干式清灰设备清灰效果进行验证,发现该设备除尘率最高可达95.3%,可满足中国西北地区大型光伏电站的清灰作业要求。     

积灰对光伏组件发电性能影响的研究

提出了一种评估积灰对光伏组件发电性能影响的有效方法及其数学模型。该方法通过监测光伏发电效率和光伏组件连续积灰的灰尘密度值,建立了输出功率退化数学模型,从理论上说明光伏组件表面积灰对发电效率的影响,为定量研究灰尘影响发电效率提供了理论支撑。搭建了试验平台进行试验研究,验证了输出功率退化数学模型的精度。     

非正常功率衰减光伏组件的发电量分析与研究

光伏组件是光伏电站的关键部件,其功率衰减将造成光伏电站的整体发电量下降,影响电站的效益。通过对连接有正常功率衰减光伏组件和非正常功率衰减光伏组件的2台逆变器的发电量数据进行分析,得出了非正常功率衰减光伏组件的衰减规律及衰减程度,可为以后深入研究提供参考。     

积灰阴影遮挡对光伏发电系统的影响

阐述了太阳能光伏电池积灰的成因、积灰的物理及化学性质和形态分类,解释了积灰的遮挡效应、腐蚀效应和热斑效应,应用MATLAB应用软件搭建光伏电池及光伏发电仿真系统,研究积灰阴影遮挡对光伏发电系统的影响。分析光伏发电系统的原理,利用MATLAB建立光伏发电系统模型,利用搭建好的模型针对光伏组件的积灰与局部阴影来进行仿真,用定性和定量分析积灰与阴影遮挡对光伏组件及其发电系统的影响,指出了对于光伏板组件上积灰清洗的重要性。     

不同纬度下光伏电站阴影的影响与分析

目前光伏阵列支架间距计算均以保证冬至日发电6h为依据,而未考虑各纬度光伏电站不同日照时长情况下因阴影差异导致的发电量损失。故本文首先计算不同纬度、不同日照时长的不可用辐射量及发电量;然后分析因此产生的投资差异;最后计算出各纬度条件下间距计算的参考值。     

Adhesional shear strength and surface analysis of a PV module deployed in harsh coastal climate

Adhesional shear strength and chemical composition at the Si/EVA interface of samples extracted from a PV module manufactured by a major manufacturer using slow-cure EVA and deployed in the hot and humid climate at Cocoa, FL were studied. Precipitation of sodium from glass superstrate and ambient, and phosphorous from dopant glass reduced adhesional strength at Si/EVA interface to 35% of that in new modules. Presence of tin at this interface has also been attributed to solder-bond corrosion by moisture and impurities Na and P. It is interesting to point out that in this case, corrosion has occurred prior to delamination.     

A simple model for PV module reflection losses under field conditions

PV module power ratings are determined at standard test conditions, which require perpendicular incident light. Under field conditions larger incidence angles occur, resulting in higher reflection losses than accounted for in the nominal power rating. In this article we will present a model to take these losses into account, and discuss some results for practical situations. From our model we conclude that the reflection losses relative to STC are determined mainly by the air glass-interface. Limited validation assuming certain spectral losses showed a rough correspondence between calculated reflection losses and experimental values on a yearly averaged basis (1.2% difference between model and experiment). Model calculations show that for modules faced towards the equator, and with a tilt angle equal to the latitude, yearly reflection losses relative to STC are about 3%. For this tilt and orientation, the losses seem to be only slightly dependent on the geographical latitude of the location. Tilt, orientation and seasonal dependence are significant. For vertically mounted PV modules (facades) near the equator the reflection losses can be quite large (up to 8%)     

An analysis of geometrical shapes for PV module glass encapsulation

In this work we simulate structured-surface covers of photovoltaic modules with different patterns in order to compare the optical performance (light trapping) of these patterns at different conditions. To achieve this, we use a new software application with an optical calculus engine. Although the primarily reflected light represents a small percentage of the total incoming energy at normal incidence and some part of that fraction will be lost due to Fresnel and absorption losses, there is a substantial increase of the final energy reaching the photocell, specially for large angles of light incidence. In particular, we analyze two different covers: an abrupt-shaped pattern of triangular form and a smoothed-shaped pattern of sinusoidal form in order to evaluate and compare their light transmission properties. We study both structures by varying their geometrical parameters, and also by considering different angles of the incoming light, and different absorption coefficients of the materials. We conclude that the use of these types of covers can improve the performance of regular photocells molding these structures in their encapsulation.     

Reflection loss analysis by optical modeling of PV module

As an evaluation method of the photovoltaic (PV) system, it is necessary to clarify loss factor which decreases system efficiency. One of the factors mentioned is the reflection loss that depends on an incident angle. It is believed that the factor is simulated by reflections and transmissions in a module. Using the optical performance of a four-layer encapsulation, a simulation was made on the reflection loss according to Fresnel's law. Further, the incident angle modification factor as the coefficient for evaluating energetic reflection loss was described by a computer program simulation. The result was that the modification factor is between 0.96 and 0.98. Consequently, to obtain the optical property of module materials, the module tilt angle and its latitude location, the simulation could give the evaluation of annual reflection losses by such a factor at various regions.     

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.     

Evaluation of electric energy performance by democratic module PV system field test

A systematic investigation has been made on annual accumulated generated PV power from different solar arrays consisting of three kinds of silicon-based solar cells. To clarify seasonal output power variations with temperature in c-Si and a-Si cells might be an important issue for the operations of PV system. It has been shown from the results that electric output power from a-Si array in summer is 20% larger than that from c-Si. On the other hand, in winter, this scene should be reverted. However, output power from c-Si array is only 5% larger than that from a-Si. The analyzed data also shows that annual accumulated electric power generated from a-Si array corresponds to 90% of its nominal efficiency in the year. While in case of c-Si array, this ratio is about 84%.     

智能光伏组件的研究与实践

光伏发电最重要的发电装置是光伏组件,所以光伏组件的质量与可靠性直接决定了整个光伏发电系统的可靠性与稳定性.设计了一种基于MOS晶体管、单片机、红外收发装置的智能光伏组件,其原理是单片机通过定时测试两路太阳电池片的输出电压来判断各路电池片的实际工作情况,根据其工作状态来控制起续流作用的MOS晶体管的工作状态,并且单片机把得到的总电量值保存在内部EEPROM中,需要了解组件自从安装后的发电总量时,用手持抄表器很方便地通过组件上的红外收发模块得到EEPROM中的数据.     

Climate-based empirical model for PV module temperature estimation in tropical environment

The paper proposes new mathematical models to estimating PV module temperature for poly and mono crystalline technologies in tropical climate such as in Malaysia. The developed models are based on measured hourly global solar radiation, ambient temperature, relative humidity, wind speed and module temperature. All data were collected over the year 2009 at GreenTech 92 kWp installed PV system in Selangor, Malaysia. The models were compared using r, MBE, RMSE, and MPE. The results showed that the proposed models give the highest value of correlation coefficient r, and good result when considering statistical indicators i.e. low RMSE, low MBE, and low MPE values. The results show that the proposed regression models have advantages over the conventional approaches for calculating the hourly and day-average PV module temperature, and give the closest results comparing to the actual measurements. The proposed approaches can be used as effective tools for predicting the PV module temperature, whether a simple PV module, open rack system, BIPV installations, or even PV/Thermal collector, in remote and rural locations with no direct measurement equipment. The proposed models can be very useful in studying PV system performance and estimating its energy output.     

Experimental studies of fault location in PV module strings

Two methods for the fault location in PV module string were experimentally studied. One was the earth capacitance measurement (ECM) and the other was the time-domain reflectometry (TDR). By ECM, the disconnection position in the string was estimated by the earth capacitance value without the effects of the irradiance change, and the estimation error was small enough to determine the disconnection position in actual repair/maintenance operation. On the other hand, TDR could detect the degradation (series resistance increase) and the positions in the string by the change of response waveform.