Soiling and other optical losses in solar‐tracking PV plants in navarra

Field data of soiling energy losses on PV plants are scarce. Furthermore, since dirt type and accumulation vary with the location characteristics (climate, surroundings, etc.), the available data on optical losses are, necessarily, site dependent. This paper presents field measurements of dirt energy losses (dust) and irradiance incidence angle losses along 2005 on a solar‐tracking PV plant located south of Navarre (Spain). The paper proposes a method to calculate these losses based on the difference between irradiance measured by calibrated cells on several trackers of the PV plant and irradiance calculated from measurements by two pyranometers (one of them incorporating a shadow ring) regularly cleaned. The equivalent optical energy losses of an installation incorporating fixed horizontal modules at the same location have been calculated as well. The effect of dirt on both types of installations will accordingly be compared. Copyright © 2010 John Wiley & Sons, Ltd.     

Global overview on grid‐parity

Grid‐parity is a very important milestone for further photovoltaic (PV) diffusion. A grid‐parity model is presented, which is based on levelized cost of electricity (LCOE) coupled with the experience curve approach. Relevant assumptions for the model are given, and its key driving forces are discussed in detail. Results of the analysis are shown for more than 150 countries and a total of 305 market segments all over the world, representing 98.0% of world population and 99.7% of global gross domestic product. High PV industry growth rates enable a fast reduction of LCOE. Depletion of fossil fuel resources and climate change mitigation forces societies to internalize these effects and pave the way for sustainable energy technologies. First grid‐parity events occur right now. The 2010s are characterized by ongoing grid‐parity events throughout the most regions in the world, reaching an addressable market of about 75–90% of total global electricity market. In consequence, new political frameworks for maximizing social benefits will be required. In parallel, PV industry tackle its next milestone, fuel‐parity. In conclusion, PV is on the pathway to become a highly competitive energy technology. Copyright © 2012 John Wiley & Sons, Ltd.     

Solar spectral influence on the performance of photovoltaic (PV) modules under fine weather and cloudy weather conditions

The performance of photovoltaic modules is influenced by solar spectrum even under the same solar irradiance conditions. Spectral factor (SF) is a useful index indicating the ratio of available solar irradiance between actual solar spectrums and the standard AM1·5‐G spectrum. In this study, the influence of solar spectrum on photovoltaic performance in cloudy weather as well as in fine weather is quantitatively evaluated as the reciprocal of SF (SF⁻¹). In the cases of fine weather, the SF⁻¹ suggests that solar spectrum has little influence (within a few %) on the performance of pc‐Si, a‐Si:H/sc‐Si, and copper indium gallium (di)selenide modules, because of the “offset effect”. The performance of a‐Si:H modules and the top layers of a‐Si:H/µc‐Si:H modules can vary by more than ± 10% under the extreme conditions in Japan. The seasonal and locational variations in the SF⁻¹ of the bottom layers are about ± several %. A negative correlation is shown between the top and bottom layers, indicating that the performance of a‐Si:H/µc‐Si:H modules does not exceed the performance, at which the currents of the top and bottom layers are balanced, by the influence of solar spectrum. In the cases of cloudy weather, the SF⁻¹ of the pc‐Si, a‐Si:H/sc‐Si, and copper indium gallium (di)selenide modules is generally higher, suggesting favorable for performance than that in fine weather. Much higher SF⁻¹ than that in fine weather is shown by the a‐Si:H module and the top layer of the a‐Si:H/µc‐Si:H module. The SF⁻¹ of the bottom layer neither simply depend on season nor on location. Copyright © 2011 John Wiley & Sons, Ltd.     

Microcontroller‐based simple maximum power point tracking controller for single‐stage solar stand‐alone water pumping system

A simple microcontroller‐based maximum power point tracking controller is proposed for a single‐stage solar stand‐alone water pumping system for remote, isolated, and nonelectrified population, where less maintenance, low cost, and an efficient system is of prime interest. It consists of a photovoltaic (PV) module, a DC–AC converter utilizing space‐vector pulse‐width modulation, an induction motor coupled with a water pump, a voltage sensor, and a current sensor. A space‐vector pulse‐width modulation‐controlled DC–AC converter aided by a fast‐acting on–off supervisory controller with a modified perturb‐and‐observe algorithm performs both the functions of converting PV output voltage to a variable voltage, variable frequency output, as well as extracting the maximum power. A limited variable step size is preferred during transient state, and a steady frequency, which is calculated on the basis of steady‐state oscillation, is set during steady state. A fast‐acting on–off supervisory controller regulates DC link voltage during steady state and enables maximum power point tracking algorithm only during transient state to draw a new voltage reference. In the event of low voltage, the controller switches off the motor but continuously scans for an available PV voltage. The system is not protected against an overcurrent because the maximum current is equal to its short circuit current. The 16‐bit microcontroller dsPIC6010A (Microchip Technology, Inc., Chandler, AZ, USA) is used to implement the control functions. The proposed controller is verified through simulation as well as tested in the laboratory prototype model. The simulation and experimental results show good correlation. Copyright © 2011 John Wiley & Sons, Ltd.     

Polycrystalline silicon PV modules performance and degradation over 20 years

The presented paper reports the results of the experimental work performed at the European Solar Test Installation, using an array of 70 polycrystalline silicon photovoltaic (PV) modules by the same manufacturer. After almost 20 years of continuous outdoor exposure, the modules were subjected to a comprehensive indoor test plan; in particular, electrical performance measurements were performed, together with a detailed visual analysis. It was also possible to perform a comparison between final and initial data (in particular IV characteristics): module average performance decay is 4.42% for the whole period. Degradation mechanisms, together with their effect on module lifetime, were also analyzed. Results of such a measurement exercise clearly show how PV device reliability over decades can guarantee safe investments, for the benefit of all PV users and stakeholders. The authors are currently installing the modules for further 20 years of outdoor exposure. Copyright © 2012 John Wiley & Sons, Ltd.     

一种并网型风光互补发电系统的建模与仿真

分析了风光互补发电系统的技术优势,设计了基于固态变压器结构的并网型风光互补发电系统。分别建立了光伏系统,风力发电系统,超级电容和蓄电池的模型,并分析各环节的控制策略,提出了基于平均功率的储能设备容量配置方法。仿真结果表明,该系统能模拟风光互补系统在不同模式下的运行特性,可以有效降低功率波动和维持电压稳定,并能在低光照强度、低风速等情况下为系统提供短时能量支撑。     

并网风光发电中混合储能系统容量优化配置

提高并网风光发电系统的调度灵活性需要引入储能技术,而储能技术研究的首要关键技术问题就是储能系统的容量配置。利用蓄电池和超级电容器的互补特性,提出了一种以优化蓄电池工作状态为原则,以提高储能系统整体经济性为目标的能量管理策略。基于该能量管理策略分析了并网风光发电系统能量损失率和能量缺失率的计算流程,根据全生命周期费用理论,建立了储能装置的年均费用函数表达式,并建立了以该函数值最小为目标,以系统能量损失率及能量缺失率等运行指标为约束的储能容量优化配置模型。运用改进混沌优化算法对实例进行了计算,验证了该优化模型与算法的正确性和有效性。     

单相无变压器光伏并网系统漏电流的研究

漏电流是研究非隔离型光伏并网系统的一个重要问题.漏电流谐振电路等效模型的建立对研究抑制漏电流至关重要.本文首先推导单相全桥并网逆变器漏电流谐振回路等效电路模型;然后详细分析了不同开关调制方式和滤波电感不对称分布对漏电流的影响,并指出电网电压对漏电流的影响不可忽略;最后介绍了一种新型无变压器拓扑结构,这种结构具有单极性调制和双极性调制优点,能够抑制共模漏电流的产生,同时提高系统的效率和并网电流质量.通过仿真和实验验证了分析结果的正确性.     

基于STM32F103芯片的光伏充电控制器设计

为了改善独立光伏发电系统中蓄电池的荷电水平,延长蓄电池的使用寿命.提出利用最大功率跟踪(MPPT)与蓄电池三段式充电相结合的充电控制策略,并基于数字控制方式,设计完成了光伏充电控制器的硬件电路和控制软件,完成了相关实验,验证了设计的有效性和正确性.     

双极型光伏并网系统逆变器故障分析

建立了双极型的光伏并网仿真模型,采用基于电导增量法的最大功率跟踪控制,并网控制通过采集电网电压参数和逆变输出电流电压参数在逆变控制电路中通过PI调节实现.实现了逆变器输出的电压和电网侧电压的同频同相.对单、双重逆变器典型故障的波形进行了分析,双重逆变器改善了输出波形,更利于电网.