Stochastic modelling of solar irradiance on horizontal and vertical planes at a northerly location

Sunshine levels incident in the plane of a photovoltaic panel are the overriding influence on electrical output, and modelling solar irradiance is therefore an essential step in the design and performance prediction of solar energy conversion systems. This study aims to assess the efficacy of SARIMA models and their potential for short-term prediction at a northerly latitude. Data was collected from a monitoring site on the roof of a 5-storey building at a city centre location in Newcastle upon Tyne, UK (latitude 55°N). Hourly and ten minute data relating to 13 and 15 day periods in two winters (1993, 1994) and two summers (1994, 1995) were utilised. Univariate stochastic modelling, using SARIMA models, is carried out for horizontal and south facing vertical solar irradiance. Results showed that these models provided a good fit for the ten minute averaged horizontal and vertical irradiance, with, on average, 82% and 85% of total variation being accounted for respectively. Use of hourly averaged data in these models gave a substantial reduction in the fit. Models for the winter data were a poorer fit than for summer for both orientations. It is concluded that the SARIMA approach can be used to develop prediction methods and to study rapid and large changes in PV output from extensive areas of solar cladding.     

基于光伏组件的太阳能资源观测

鉴于太阳能资源的测量和评价是太阳能开发利用的重要基础,按照光伏电池两种主要安装方式(倾斜固定和太阳跟踪),利用单晶、多晶和非晶三种典型的光伏组件设计进行了太阳能光伏资源观测试验,获得了各季节典型晴天条件下各类型光伏组件辐照度的日变化特征和倾斜面光伏组件一年中月均每日可发电量的极大值、极小值及其月份。通过对比各类型光伏组件在太阳跟踪器上和纬度倾斜面上光伏辐照度变化,得出跟踪光伏组件日均光伏曝辐量与倾斜光伏组件日均光伏曝辐量的相比较优势。根据光伏组件的观测结果推算出各类型光伏组件的光伏反演辐照度,与气象辐射观测用总辐射表的总辐射辐照度趋势非常一致,在太阳能光伏主要利用时段相对误差基本在10%以内。     

PV-GIS: a web-based solar radiation database for the calculation of PV potential in Europe

Solar radiation is a key factor determining electricity produced by photovoltaic (PV) systems. This paper presents a solar radiation database of Europe developed in the geographical information system, and three interactive web applications providing an access to it. The database includes monthly and yearly average values of the global irradiation on horizontal and inclined surfaces, as well as climatic parameters needed for an assessment of the potential PV electricity generation (Linke atmospheric turbidity, the ratio of diffuse to global irradiation, an optimum inclination angle of modules to maximize energy yield). In the first web application, a user may browse radiation maps and query irradiation incident on a PV module for different inclination angles. The second application simulates daily profiles of irradiance for a chosen month and module inclination and orientation. The third web application estimates electricity generation for a chosen PV configuration. It also calculates optimal inclination and orientation of a PV module for a given location. The database and the applications are accessible at http://re.jrc.cec.ev.int/pvgis/pv/imaps/imaps.htm.     

Feasibility analysis of solar photovoltaic array cladding on commercial towers in Doha,Qatar – a case study

Building-integrated photovoltaic (BIPV) technology has become a major area of research due to environ-mental concerns. This article studies the feasibility of cladding high-rise towers in Doha with solar photovoltaic modules. Specifically, the case of the Qatar Financial Centre (QFC) is discussed. The major aim of the work is to evaluate the technical feasibility, economic impact and environmental effects of using photovoltaic panels on commercial towers in Qatar. Experimental data on solar irradiance and the effect of shading on the QFC Tower are presented. Numerical calculations are done using solar pathfinder software. The studies show that, although there is a significant amount of saving in CO₂ emission by using BIPV on towers in Doha, the payback period is still very long due to the cheaper cost of grid electricity in Qatar and poor conversion efficiency of PV panels. The complete system layout is presented and viable solutions are investigated.     

Impact of solar radiation variation on the optimal tilted angle for fixed grid-connected PV array—case study in Beijing

A key design parameter for fixed grid-connected photovoltaic (PV) arrays, the optimal tilt angle, does not only depend on the geographic location but is also directly affected by atmospheric conditions. In this paper, long-term variations of solar radiation (i.e. global solar irradiance, direct horizontal irradiance, diffuse irradiance, and ratios of direct and diffuse irradiance) in Beijing are considered to determine their effect on the optimal tilt angle for a fixed grid-connected PV array. We found that there is a declining trend in global solar irradiance over the past 55 years, mainly caused by the decreased direct horizontal irradiance. In contrast, the decline of diffuse irradiance is not obvious, leading to a considerable decrease in the direct irradiance ratio and consequent increase in the diffuse irradiation ratio. Likewise, the long-term optimal tilt angle shows a downward trend. Compared with the optimum in the 1960s, the optimal tilt angle has decreased by 2° in 2011–2015. These results suggest that the declining trend in the optimal tilt angle is mainly caused by the decrease in direct irradiance ratio, which is highly related to atmospheric conditions. Therefore, the design and construction of PV power stations must consider the variations of atmospheric conditions and solar irradiance to determine the optimal tilt angle.     

Impact of environment factors on solar cell parameters of a-Si∥μc-Si photovoltaic modules

The behavior of amorphous silicon∥micro crystalline silicon (a-Si∥μc-Si) tandem-type photovoltaic (PV) module is complex because the output current is limited by the lower current component cell. Also, the outdoor behaviors are not fully understood. The impact of environment factors on solar cell parameters of a-Si∥μc-Si PV module was quantitatively analyzed and the module was compared with other silicon-based PV modules (single crystalline silicon (sc-Si) and amorphous silicon (a-Si)). The contour maps of solar cell parameters were constructed as a function of irradiance and module temperature. The contour map of a-Si∥μc-Si PV modules is similar to that of a-Si modules. The results imply that output characteristics of a-Si∥μc-Si PV modules are mainly influenced by the a-Si top cell. Furthermore, the efficiency of a-Si∥μc-Si PV modules was compared other solar cell parameters and the contour map of efficiency is similar to that of fill factor.     

Comparative analysis of the infield response of five types of photovoltaic modules

Five types of photovoltaic (PV) modules were comparatively analyzed considering the electrical output, efficiency and relative loss in efficiency, based on infield data collected in a temperate mountain climate, over 14 months. The mono-, poly-crystalline silicon, CdTe, CIS and CIGS modules were mounted on two identical platforms, installed close to a row of buildings. Based on the data collected from individual or groups of modules on the two platforms, analyses focused on the photovoltaic output, considering: the mean monthly values; the influence of the neighboring buildings; the influence of the irradiance, temperature and wind in different seasons (winter, summer); the influence of tracking on each PV module type. The qualitative analysis shows that small PV platforms installed in the built environment require accurate investigations on the air currents with influence on snow and frost retention/melting and water vapor condensation. In the temperate climate, with snowy winters and rather warm summers, the best performing modules are of poly-crystalline silicon; among thin film modules, the best output corresponds to CIGS, while the steadiest efficiency corresponds to CdTe. Tracking has a “leveling” effect on the conversion efficiency, making the PV output more predictable during days with preponderant direct solar irradiance.     

Statistical investigation of the optimal averaging time for solar irradiance on horizontal and vertical surfaces in the UK

As output from photovoltaic (PV) panels is closely related to sunlight levels, monitoring solar irradiance levels is crucial for system design and predictive purposes. With advances in PV technology, urban sites at northerly locations, where both horizontal and vertical solar irradiance make significant contributions, are becoming increasingly important. The aim of this paper is to compare solar irradiance for horizontal and vertical orientations and to assess the relative effectiveness of differing averages, from 10 min to 1 h, for use in short-term prediction of solar irradiance levels for a UK site. Vertical and horizontal solar irradiance observations were collected from a monitoring station on the roof of a five-storey building at an urban site in Newcastle-upon-Tyne, UK (latitude 55°N). 10-min data was collected for 13- or 15-day periods in two summers (1994, 1995) and two winters (1993, 1994). Although mean levels for horizontal and vertical irradiance were different, as expected, general patterns were very similar indicating the possibility of predicting vertical irradiance from horizontal at the same location. 10-min, 20-min, 30-min and 1-h averaging times were compared utilising autocorrelation coefficients and ARIMA models to assess the information lost when using longer averaging intervals. For consideration of short-term changes, 10-min averages were most informative whilst hourly averages were substantially poorer.     

Effect of spectral irradiance distribution on the outdoor performance of amorphous Si//thin-film crystalline Si stacked photovoltaic modules

Effects of spectral irradiance distributions on the outdoor performance of amorphous Si//thin-film crystalline Si stacked photovoltaic (PV) modules installed at Shiga-prefecture in Japan have been investigated. Outdoor solar spectrum measurements revealed that more than 95% of annual total spectra were blue-rich compared to AM1.5 standard solar spectrum. The outdoor performance of the modules had a higher spectral dependence than that of polycrystalline Si modules. Also, the peak of the histogram of annual spectral indexes well corresponded to the peak of the outdoor performance. The results indicate that the actual spectral irradiance distribution is important in designing stacked PV modules.     

The coupling factor: A new metric for determining and controlling the efficiency of solar photovoltaic power utilization

The production of electricity and hydrogen in a renewable fashion, such as using solar energy, can provide a clean and sustainable energy source for electric-powered vehicles, including fuel-cell and battery-electric vehicles. Our research on generating hydrogen and charging batteries using renewable solar photovoltaic (PV) electricity has led to the development of a simple and convenient new metric called the coupling factor that describes the fraction of the maximum PV power transferred to electrical loads. The keystone of the coupling factor concept is a regression model to calculate the maximum PV voltage, current, and power as a function of the instantaneous incident solar irradiance and the photovoltaic module temperature. The coupling factor can range from zero to one, i.e., no transfer of power from the PV system to the load, to complete transfer of the PV power. We describe the derivation of regression models to compute important PV electrical output variables, such as the open circuit voltage, the short circuit current, the maximum power point voltage, the maximum power point current, and the coupling factor as a function of the fundamental measured variables affecting those quantities. The models are derived for PV modules used in our previous research to power an electrolyzer and charge high-voltage batteries. In addition, we develop models for other modules using PV cell technologies different from those used in our PV system. Some of the calculated quantities are compared to measurements for our PV system. The usefulness of these quantities, and especially the coupling factor, in rating the transfer of PV power to electrolyzer and battery loads, is illustrated. Finally, we discuss how the predicted maximum power point voltage can be used for real-time control and efficiency optimization of a dynamic PV-load system.     

Mapping the performance of PV modules, effects of module type and data averaging

A method is presented for estimating the energy yield of photovoltaic (PV) modules at arbitrary locations in a large geographical area. The method applies a mathematical model for the energy performance of PV modules as a function of in-plane irradiance and module temperature and combines this with solar irradiation estimates from satellite data and ambient temperature values from ground station measurements. The method is applied to three different PV technologies: crystalline silicon, CuInSe₂ and CdTe based thin-film technology in order to map their performance in fixed installations across most of Europe and to identify and quantify regional performance factors. It is found that there is a clear technology dependence of the geographical variation in PV performance. It is also shown that using long-term average values of irradiance and temperature leads to a systematic positive bias in the results of up to 3%. It is suggested to use joint probability density functions of temperature and irradiance to overcome this bias.     

A power-rating model for crystalline silicon PV modules

A model for the performance of generic crystalline silicon photovoltaic (PV) modules is proposed. The model represents the output power of the module as a function of module temperature and in-plane irradiance, with a number of coefficients to be determined by fitting to measured performance data from indoor or outdoor measurements. The model has been validated using data from 3 different modules characterized through extensive measurements in outdoor conditions over several seasons. The model was then applied to indoor measurement data for 18 different PV modules to investigate the variability in modeled output from different module types. It was found that for a Central European climate the modeled output of the 18 modules varies with a standard deviation (SD) of 1.22%, but that the between-module variation is higher at low irradiance (SD of 3.8%). The variability between modules of different types is thus smaller than the uncertainty normally found in the total solar irradiation per year for a given site. We conclude that the model can therefore be used for generalized estimates of PV performance with only a relatively small impact on the overall uncertainty of such estimates resulting from different module types.     

Hybrid photovoltaic/thermal solar systems

We present test results on hybrid solar systems, consisting of photovoltaic modules and thermal collectors (hybrid PV/T systems). The solar radiation increases the temperature of PV modules, resulting in a drop of their electrical efficiency. By proper circulation of a fluid with low inlet temperature, heat is extracted from the PV modules keeping the electrical efficiency at satisfactory values. The extracted thermal energy can be used in several ways, increasing the total energy output of the system. Hybrid PV/T systems can be applied mainly in buildings for the production of electricity and heat and are suitable for PV applications under high values of solar radiation and ambient temperature. Hybrid PV/T experimental models based on commercial PV modules of typical size are described and outdoor test results of the systems are presented and discussed. The results showed that PV cooling can increase the electrical efficiency of PV modules, increasing the total efficiency of the systems. Improvement of the system performance can be achieved by the use of an additional glazing to increase thermal output, a booster diffuse reflector to increase electrical and thermal output, or both, giving flexibility in system design.     

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。     

非晶硅太阳能光伏/光热空气集热器性能对比实验研究

文章设计了新型非晶硅太阳能PV/T空气集热器,该空气集热器能够解决传统太阳能PV/T热水器在高温波动情况下,晶硅电池热应力大的问题,同时避免了冬季管道发生霜冻的现象。文章通过实验对比,分析了非晶硅太阳能PV/T空气集热器、单独非晶硅光伏电池和传统太阳能空气集热器的能量效率和[火用]效率的差异。分析结果表明:非晶硅太阳能PV/T空气集热器的平均热效率为45.70%,比传统太阳能空气集热器的平均热效率降低了约25.88%;当空气质量流量增大至0.048 kg/s时,非晶硅太阳能PV/T空气集热器中的非晶硅光伏电池的平均电效率高于单独非晶硅光伏电池,它们的平均电效率分别为4.70%,4.54%;非晶硅太阳能PV/T空气集热器的总[火用]效率高于传统太阳能空气集热器的热[火用]效率和单独非晶硅光伏电池的电[火用]效率,非晶硅太阳能PV/T空气集热器总[火用]效率最大值为7.14%。文章的分析结果为非晶硅太阳能PV/T空气集热器的推广提供了参考。     

Solar radiation resource assessment by means of silicon cells

To provide an accurate solar resource assessment, radiometric stations measuring global, diffuse, and direct irradiance must be widespread. Nevertheless, the high capital costs of thermopile instruments, usually used in pyranometry, represent an important obstacle. Therefore, silicon photovoltaic sensors have emerged as a more accessible alternative than standard thermopile sensors. However, their temperature and spectral responses must be taken into account in order to match silicon cells and thermopile responses. Global and diffuse irradiance have been measured from early 1990 to the end of 1992 in Almería, southeastern Spain, by means of thermopile and photovoltaic sensor. Polar axis shadowbands were employed to measure the diffuse irradiance. These 10-minute coincident data sets, covering a complete range of atmospheric conditions, have been used to develop a correction procedure for the silicon detector measurements. Before the correction procedure was applied severe discrepancies were found, especially for the diffuse irradiance measurements performed under clear skies. Results of the correction method applied to an independent data set show a remarkable improvement. After correction, the comparison of silicon cell measurements with those obtained by means of thermopile pyranometers leads to a root mean square deviation of about 4% and 5% over the mean value of global and diffuse horizontal irradiance, respectively.     

蝶式光伏发电聚光器的研制

通过跟踪聚光的方法,增加太阳光伏电池板的光照强度,使得同样数量的光伏电池板产生更多电能,并大幅度降低光伏发电系统的成本。介绍了一种自动跟踪太阳的蝶式光伏发电聚光器及其聚光参数优化过程,在保证聚光器的机械强度时得到了最佳聚光比。     

Estimation of irradiance and outdoor performance of photovoltaic modules by meteorological data

Three environmental factors of irradiance, solar spectral distribution and module temperature greatly affect the performances of photovoltaic (PV) modules. If the environmental factors can be estimated by basic meteorological data (BMD) announced by an official organization in various areas, the performances of PV modules can be estimated easily. In this study, a relationship between the environmental factors and the BMD was analyzed. The performances of Si-based (crystalline Si and thin-film Si) PV modules were estimated by the relationship. As a result, errors between the estimation and actual performances in the crystalline Si and thin-film PV modules were within 1.88% and 0.58% in Kusatsu city, Japan (34°58′N, 135°57′E). This methodology can be useful for rating the performance of PV modules at various areas.     

Estimation of the energy of a PV generator using artificial neural network

The integration of grid-connected photovoltaic (GCPVS) systems into urban buildings is very popular in industrialized countries. Many countries enhance the international collaboration efforts which accelerate the development and deployment of photovoltaic solar energy as a significant and sustainable renewable energy option. A previous method, based on artificial neural networks (ANNs), has been developed to electrical characterisation of PV modules. This method was able to generate V–I curves of si-crystalline PV modules for any irradiance and module cell temperature. The results showed that the proposed ANN introduced a good accurate prediction for si-crystalline PV modules performance when compared with the measured values. Now, this method, based on ANNs, is going to be applied to obtain a suitable value of the power provided by a photovoltaic installation. Specifically this method is going to be applied to obtain the power provided by a particular installation, the “Univer generator”, since modules used in these works were the same as the ones used in this photovoltaic generator.     

Uniqueness verification of solar spectrum index of average photon energy for evaluating outdoor performance of photovoltaic modules

To analyze the effect of a spectral irradiance distribution of solar spectra on the outdoor performance of photovoltaic (PV) modules, an index for the spectral distribution is needed. Average photon energy (APE) which represents the average energy per photons included in a spectrum is one of these. In this study, the uniqueness of APE to the spectral irradiance distribution was statistically analyzed to assure that an APE value uniquely yields the shape of a solar spectrum. The similar methodology adopted in International Electrotechnical Commission to rate the spectral matching of a solar simulator was used for the analysis. The results showed that an APE value yielded a spectral irradiance distribution with quite small standard deviation. The analysis using APE showed that the outdoor performance of crystalline Si PV modules depended almost only on a module temperature, while that of amorphous Si ones mainly depended on APE. The behaviors were reasonable considering from the operation mechanisms of the PV modules. These results demonstrate that APE is a reasonable and useful index to describe the spectral irradiance distribution for evaluating the outdoor performance of PV modules.