Performance comparison of AlGaAs,GaAs and InGaP tunnel junctions for concentrated multijunction solar cells

Four tunnel junction (TJ) designs for multijunction (MJ) solar cells under high concentration are studied to determine the peak tunnelling current and resistance change as a function of the doping concentration. These four TJ designs are: AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs. Time‐dependent and time‐average methods are used to experimentally characterize the entire current–voltage profile of TJ mesa structures. Experimentally calibrated numerical models are used to determine the minimum doping concentration required for each TJ design to operate within a MJ solar cell up to 2000‐suns concentration. The AlGaAs/GaAs TJ design is found to require the least doping concentration to reach a resistance of <10⁻⁴ Ω cm² followed by the GaAs/GaAs TJ and finally the AlGaAs/AlGaAs TJ. The AlGaAs/InGaP TJ is only able to obtain resistances of ≥5 × 10⁻⁴ Ω cm² within the range of doping concentrations studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparison of potential solar electricity output from fixed‐inclined and two‐axis tracking photovoltaic modules in Europe

We present an approach to determine the potential energy gains of flat plate non‐concentrating photovoltaic systems for the case of two‐axis tracking and two inclination angles with fixed orientation (assuming biannual adjustment) compared to the configuration of single fixed optimum angle. The calculation is based on the Photovoltaic Geographic Information System (PVGIS), which integrates modelling tools with the pan‐European solar radiation database. The results indicate that in the case of a PV system with two seasonal inclination angles, the maximum yearly gains, compared to the single fixed optimum angle, do not exceed 60–70 kWh per kW_p in the Mediterranean region, while in the Baltic and North Sea regions this configuration gives less than 20 kWh extra. For the case of two‐axis tracking, the relative energy gain compared to single fixed optimum angle is highest in the Northern latitudes but the absolute gain is much higher in the South. Typical yearly gains in Portugal and the Mediterranean region are in the range of 400–600 kWh per kW_p. The smallest absolute increase is found in the Northwest and Central Europe including the British Isles, where it is lower than 250 kWh per kW_p. For crystalline silicon we also investigate the effects of temperature and shallow‐angle reflectivity on the comparison between fixed and tracking systems. While both effects reduce the overall energy output, the temperature degradation is stronger for tracking systems while the reflectivity reduces output more for fixed systems. The combined effect is almost equal for fixed and two‐axis tracking systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Modeling of concentrating photovoltaic and thermal systems

An energy balance model for concentrating photovoltaic and thermal (CPVT) systems is presented. In the model, the CPVT system and its environment are represented using a set of input parameters. The main outputs of the model are the system's electrical and thermal efficiencies. The model accounts for optical losses. Thermal losses are derived from a thermal network model of the hybrid receiver. The solar cell performance is modeled as a function of the temperature and the irradiance. The robustness of the model is demonstrated by a sensitivity analysis of all input parameters. The influence of the operating temperature on the electrical and thermal performances and the overall efficiency of the CPVT system are discussed. The limiting cases of maximum electrical and thermal power outputs are presented. Further, the influence of the concentration ratio on the electrical and thermal performance and on the partitioning of these two power outputs is analyzed in detail. It is shown that high concentration reduces the thermal losses considerably and increases the electrical efficiency. At concentration ratios above 300, the system operates with an overall efficiency of 75% at temperatures up to 160 °C. Copyright © 2012 John Wiley & Sons, Ltd.     

Economic competitiveness of III–V on silicon tandem one‐sun photovoltaic solar modules in favorable future scenarios

Tandem modules combining a III–V top cell with a Si bottom cell offer the potential to increase the solar energy conversion efficiency of one‐sun photovoltaic modules beyond 25%, while fully utilizing the global investment that has been made in Si photovoltaics manufacturing. At present, the cost of III–V cells is far too high for this approach to be competitive for one‐sun terrestrial power applications. We investigated the system‐level economic benefits of both GaAs/Si and InGaP/Si tandem modules in favorable future scenarios where the cost of III–V cells is substantially reduced, perhaps to less than the cost of Si cells. We found, somewhat unexpectedly, that these tandems can reduce installed system cost only when the area‐related balance‐of‐system cost is high, such as for area‐constrained residential rooftop systems in the USA. When area‐related balance‐of‐system cost is lower, such as for utility‐scale systems, the tandem module offers no benefit. This is because a system using tandem modules is more expensive than one using single‐junction Si modules when III–V cells are expensive, and a system using tandem modules is more expensive than one using single‐junction III–V modules when III–V cells are inexpensive. Copyright © 2016 John Wiley & Sons, Ltd.     

Optimal sizing and life cycle assessment of residential photovoltaic energy systems with battery storage

This paper presents the optimal sizing and life cycle assessment of residential photovoltaic (PV) energy systems. The system consists of PV modules as the main power producer, and lead–acid batteries as the medium of electricity storage, and other essential devices such as an inverter. Five‐parameter analytic PV cell model is used to calculate the energy production from the modules. Electrical needs for a family living under normal conditions of comfort are modelled and used within simulation of the system performance, with an average daily load of approximately 9·0 kWh. The system's performance simulations are carried out with typical yearly solar radiation and ambient temperature data from five different sites in Turkey. The typical years are selected from a total of 6 years data for each site. The life cycle cost of the PV system is analysed for various system configurations for a 20‐year system life. The role of the batteries in PV energy systems are analysed in terms of the cost and power loss. The system performance is analysed as a function of various parameters such as energy production and cost. It is shown that these change substantially for different system configurations and locations. The life cycle assessment of the energy system described was also carried out to determine the environmental impact. It was found that, with the conservative European average electricity mix, energy pay back time (EPBT) is 6·2 years and CO₂ pay back time is 4·6 years for the given system. Copyright © 2007 John Wiley & Sons, Ltd.     

Geographical variation of the conversion efficiency of crystalline silicon photovoltaic modules in Europe

We present a geographical assessment of the performance of crystalline silicon photovoltaic (PV) modules over Europe. We have developed a method that is based on a material specific analytical expression of the PV conversion efficiency, relative to nominal efficiency, as a function of module temperature and irradiance. This method is combined with a climate database that includes average daytime temperature and irradiance profiles. It is found that the geographical variation in ambient temperature and yearly irradiation causes a decrease in overall yearly PV performance from 3 to 13% relative to the performance under Standard Test Conditions, with the highest decrease found in the Mediterranean region. Based on the above results we developed a simplified linear expression of the relative PV module efficiency that is a simple function of yearly total irradiation and yearly average daytime temperature. The coefficients to the linear expression are found by fitting to the map resulting from the above‐mentioned analytical approach. The prediction of total yearly PV output from this linear fit deviates less than 0·5% from the more detailed calculation, thus providing a faster and more simplified alternative to the yield estimate, in the case when only limited climate data are available. Copyright © 2008 John Wiley & Sons, Ltd.     

复杂地形下光伏电站间距、倾角和方位角的研究

本项目研究如何在复杂地形上合理的布置光伏组件。为今后山地、丘陵等复杂地形条件下的光伏发电站的设计提供更加准确的设计依据,更进一步提高了复杂地形条件下的光伏发电站发电量计算的准确度。     

Analysis of one‐axis tracking strategies for PV systems in Europe

We present a method for estimating the energy output from one‐axis tracking non‐concentrating PV systems and compare the yields from different configurations. The method is based on the use of solar radiation and temperature databases and models for the performance of PV modules under given geographic conditions. In the resulting maps of energy yield for Europe it is found that there are two different one‐axis configurations that perform almost as well as a full two‐axis sun‐tracking system: one with a vertical axis and inclined modules, and the other with an inclined axis directed north–south and modules in the plane of the axis. When the inclination angles of the modules are optimized, these two configurations have an energy yield compared to an optimal fixed mounting that is approximately 30% higher in southern Europe, about 20–25% higher in central Europe, and up to 50% higher in northern Scandinavia. Compared to the two‐axis tracking, the yields are only 1–4% lower, making such one‐axis tracking systems very attractive in terms of performance relative to technical complexity and price. Copyright © 2010 John Wiley & Sons, Ltd.     

An analysis of reliability in the early stages of photovoltaic systems in Japan

In order to disseminate Photovoltaic (PV) technologies into the energy network, the cost down is not only important, but also improving the performance of the PV system is significant issues. Long‐term reliability is one of the most important issues in terms of PV system performance. Previous researches were mainly focused on the reliability of PV modules, but the PV system is composed of a power conditioner, wiring, junction box, and so on. To improve the reliability of PV systems, it is important to accumulate trouble cases focused on all components of PV system. In this paper, we aim at evaluation of the reliability for the PV system on the early stages of PV system's lifetime by using large number of Japanese PV systems' data from the field Test in Japan. New Energy and Industrial Technology Development Organization has been running the “Field test project in Japan” from 1992. In this project, PV system users have cooperated with the collection of monitoring data and reported on the information of maintenance and certain failures of PV systems for 4 years after installation of PV system. Using those reports each year of installation, we evaluated reliability of PV systems by means of parameters such as Mean Time Between Failure, Mean Time To Repair, and the suspension time of PV system. As a result, the main trouble of PV systems was related power conditioner, and a few trouble of PV module was caused by typhoon. Moreover, the trend of the failure rate before FY 2000 of installation was demonstrated as the trend of initial failure in “bathtub curve;” however, the trend of its after FY 2001 of installation was indicated as the accidental failure in “bathtub curve.” Further, the operator simply forgot to restart the power conditioner after maintenance or suspensions of PV system in many trouble cases, and the user did not notice that it had been suspended for a while. These trouble cases can be avoidable easily through the effective alarm such as error message of power conditioner systems with monitoring systems. Thereby, monitoring with the evaluation method of PV systems is one of the important technologies due to the long‐term reliability and stable operation. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental system for current–voltage curve measurement of photovoltaic modules under outdoor conditions

This paper describes an experimental system developed in the photovoltaic laboratory at the University of Málaga (Spain) to measure the current–voltage curve of photovoltaic modules under outdoor conditions. The measurement is performed in an automated way by employing commercial instruments controlled by a computer using the GPIB standard. Several modules, selected sequentially through a set of relays, are biased by a four‐quadrant power supply while a function generator synchronizes two multimeters in order to acquire voltage and current values. The measurement uncertainties were also estimated. The proposed method for synchronizing the voltage and current measurements ensures that these measurements are performed simultaneously; this means that the estimated uncertainty is lower than those obtained using other previously proposed methods. The main electrical parameters are estimated. A user‐friendly application allows the user to configure several parameters, such as bias rate, voltage, and current limits and the number of points of the curve. Copyright © 2011 John Wiley & Sons, Ltd.     

Life cycle analysis of organic photovoltaic technologies

Organic solar cells, both in the hybrid dye sensitized technology and in the full organic polymeric technology, are a promising alternative that could supply solar electricity at a cost much lower than other more conventional inorganic photovoltaic technologies. This paper presents a life cycle analysis of the laboratory production of a typical bulk heterojunction organic solar cell and compares this result with those obtained for the industrial production of other photovoltaic technologies. Also a detailed material inventory from raw materials to final photovoltaic module is presented, allowing us to identify potential bottlenecks in a future supply chain for a large industrial output. Even at this initial stage of laboratory production, the energy payback time and CO₂ emission factor for the organic photovoltaic technology is of the same order of other inorganic photovoltaic technologies, demonstrating that there is plenty of room for improvement if the fabrication procedure is optimized and scaled up to an industrial process. Copyright © 2010 John Wiley & Sons, Ltd.     

基于SPOC的混合式学习的学习分析与应用

在自主开发的个性化教学平台基础上,探索了课堂教学与网络MOOC教学相融合的混合学习模式.根据学习分析结果,有针对性地对学生的学习过程进行干预,并发现教学中的问题,进而不断改善混合学习的教学设计与实施.研究表明, 从群体的行为数据均值考虑,学生的在线学习表现和学生成绩是正相关的,网上MOOC学习对学习效果的提升有较大促进作用.     

Characterization of the spatial distribution of irradiance and spectrum in concentrating photovoltaic systems and their effect on multi‐junction solar cells

The irradiance and spectral distribution cast on the cell by a concentrating photovoltaic system, typically made up of a primary Fresnel lens and a secondary stage optical element, is dependent on many factors, and these distributions in turn influence the electrical performance of the cell. In this paper, the effect of spatial and spectral non‐uniform irradiance distribution on multi‐junction solar cell performance was analyzed using an integrated approach. Irradiance and spectral distributions were obtained by means of ray‐tracing simulation and by direct imaging at a range of cell‐to‐lens distances. At the same positions, I–V curves were measured and compared in order to evaluate non‐uniformity effects on cell performance. The procedure was applied to three different optical systems comprised a Fresnel lens with a secondary optical element consisting of either a pyramid, a dome, or a bare cell. Copyright © 2011 John Wiley & Sons, Ltd.     

Machine Learning Assisted Analysis,Prediction, and Fabrication of High-Efficiency CZTSSe Thin Film Solar Cells

The Earth-abundant element-based Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber is considered as a promising material for thin-film solar cells (TFSCs). The current record power conversion efficiency (PCE) of CZTSSe TFSCs is ≈13%, and it's still lower than CdTe and CIGS-based TFSCs. A further breakthrough in its PCE mainly relies on deep insights into the various device fabrication conditions; accordingly, the experimental–oriented machine learning (ML) approach can be an effective way to discover key governing factors in improving PCE. The present work aims to identify the key governing factors throughout the device fabrication processes and apply them to break the saturated PCE for CZTSSe TFSCs. For realization, over 25,000 data points were broadly collected by fabricating more than 1300 CZTSSe TFSC devices and analyzed them using various ML techniques. Through extensive ML analysis, the i-ZnO thickness is found to be the first, while Zn/Sn compositional ratio and sulfo-selenization temperature are other key governing factors under thin or thick i-ZnO thickness to achieve over 11% PCE. Based on these key governing factors, the applied random forest ML prediction model for PCE showed Adj. R² = >0.96. Finally, the best-predicted ML conditions considered for experimental validation showed well-matched experimental outcomes with different ML models.     

Energy,cost and LCA results of PV and hybrid PV/T solar systems

Hybrid photovoltaic/thermal (PV/T) solar systems provide a simultaneous conversion of solar radiation into electricity and heat. In these devices, the PV modules are mounted together with heat recovery units, by which a circulating fluid allows one to cool them down during their operation. An extensive study on water‐cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. In this paper the electrical and thermal efficiencies are given and the annual energy output under the weather conditions of Patras is calculated for horizontal and tilted building roof installation. In addition, the costs of all system parts are included and the cost payback time is estimated. Finally, the methodology of life cycle assessment (LCA) has been applied to perform an energy and environmental assessment of the analysed system. The goal of this study, carried out at the University of Rome ‘La Sapienza’ by means of SimaPro 5·1 software, was to verify the benefits of heat recovery. The concepts and results of this work on energy performance, economic aspects and LCA results of modified PV and water‐cooled PV/T solar systems, give a clear idea of their application advantages. From the results, the most important conclusion is that PV/T systems are cost effective and of better environmental impact compared with standard PV modules. Copyright © 2005 John Wiley & Sons, Ltd.     

基于回归分析的迎峰度夏用电量分析

利用回归分析算法,提出了一种迎峰度夏期间最高气温与日用电量关系分析方法,首先利用皮尔森相关系数对度夏期间的最高气温和日用电量相关程度进行定量分析,然后利用回归分析算法建立最高气温和日用电量的拟合函数,并利用最小二乘法进行求解,得到最高气温和日用电量相关关系的定量分析结果。研究结果表明,提出的度夏期间用电量分析方法能够定量地给出气温变化导致的用电量变化情况,并能根据分析结果对未来几天的日用电量进行准确预测。     

志愿计算系统时延分析

志愿计算(Volunteer Computing)系统是一种分布式计算系统,它利用全球空闲计算资源实现海量科学计算.随着志愿计算的广泛应用,系统时延性能分析变得日益重要.现有文献主要通过仿真和实验观察其时延特性,并不能深入分析系统参数的影响.为此,提出了一种新的数学模型对志愿计算系统时延特性进行分析.志愿计算系统可以建模为一个变速率服务的单服务台排队系统.理论分析表明,系统的平均队长与服务速率方差之间存在单调递增的关系.因此,系统在服务速率方差趋于0和无穷大两个极端情况下的平均队长分别为系统平均队长的下界和上界,而在这两种极端情况下,可以通过对系统模型的简化求得系统的平均队长.仿真结果验证了该方法所求平均队长上下界的正确性和准确性.     

Performance,cost and life‐cycle assessment study of hybrid PVT/AIR solar systems

An alternative and cost‐effective solution to building integrated PV systems is to use hybrid photovoltaic/thermal (PV/T) solar systems. These systems consist of PV modules with an air channel at their rear surface, where ambient air is circulating in the channel for PV cooling and the extracted heat can be used for building thermal needs. To increase the system thermal efficiency, additional glazing is necessary, but this results in the decrease of the PV module electrical output from the additional optical losses of the solar radiation. PV/T solar systems with air heat extraction have been extensively studied at the University of Patras. Prototypes in their standard form and also with low‐cost modifications have been tested, aiming to achieve improved PV/T systems. An energetic and environmental assessment for the PV and PV/T systems tested has been performed by the University of Rome ‘La Sapienza’, implementing the specific software SimaPro 5·1 regarding the life‐cycle assessment (LCA) methodology applied. In this paper electrical and thermal energy output results for PV and PV/T systems are given, focusing on their performance improvements and environmental impact, considering their construction and operation requirements. The new outcome of the study was that the glazed type PV/T systems present optimum performance regarding energy, cost and LCA results. Copyright © 2005 John Wiley & Sons, Ltd.     

无人机直喷发动机谐振进气系统设计及仿真分析

本文针对一无人机用四缸两冲程汽油直喷发动机,应用GT-Power软件建立了仿真模型,并通过对气缸压力和发动机扭矩的仿真结果与实验数据进行对比,验证了所建模型的合理可用性。运用亥姆霍兹理论设计了谐振进气系统,并利用软件自带的优化工具,分析了谐振器及进气系统管道长度对发动机动力性能的影响。仿真结果表明,进行参数优化后,该谐振进气系统使得无人机动力性能得到进一步提升。