Measuring diffuse, direct, and global irradiance using a sky imager

Kurtz, Ben; Kleissl, Jan

doi:10.1016/j.solener.2016.11.032

Cited by 31 publications

(16 citation statements)

References 16 publications

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“…There are several methods to do this. Some of the best known are the Angström Turbidity Coefficient and the Linke Factor [28,59,60].…”

Section: Attenuation Processes Of Solar Radiationmentioning

confidence: 99%

“…1.06 (27) The diffuse radiation due to the presence of aerosols is obtained from Eq. (28). The calculation of diffuse irradiance by multiple reflections (I dm ) requires the reflection coefficients of each different surface (ρ g ).…”

Section: Bird and Hulstrom Model And Improvementsmentioning

confidence: 99%

“…The forecasted irradiance showed a slight positive mean bias error in the intra-day forecasting compared with the observation. Kurtz et al [28] have measured diffuse, direct, and global irradiance using a sky imager. This technique is used for aerosol characterization, cloud detection, and solar forecasting.…”

Section: Introductionmentioning

confidence: 99%

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Attenuation processes of solar radiation. Application to the quantification of direct and diffuse solar irradiances on horizontal surfaces in Mexico by means of an overall atmospheric transmittance

Gutiérrez-Trashorras

Villicaña-Ortíz

Álvarez-Álvarez

et al. 2018

Renewable and Sustainable Energy Reviews

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A B S T R A C TQuantifying incident solar radiation on a surface is a complex task that requires the knowledge of geometric, geographical, astronomical, physical and meteorological characteristics of the location.The aim of this paper is to analyze the attenuation processes of the solar radiation and to review the scientific works in this field, specifically the analytical models for solar irradiance calculation, as well as to establish an alternative method to compute the magnitude of the overall atmospheric transmittance.Analytical models have been developed since 1940 and they have been improving in precision and complexity. Up until now, the Bird & Hulstrom model is the most complete and accurate of them all. The main disadvantage of this model is that a great number of equations and parameters such as temperature, sunshine hours, humidity, etc. are required.In this paper, a very fast and accurate new method is developed to quantify solar irradiances at any site. The analysis shows that the parameters required are only the type of climate, altitude and state of the atmosphere. This method also allows to quantify the influence of the turbidity degree in both direct and diffuse irradiances. That information is essential to select which solar technologies are suitable in each place.As an application, the new method has been implemented and characterized in Mexico. Solar energy is an abundant resource in Mexico, and there are some studies about the solar energy potential in that country, but the influence of physical and meteorological factors on the solar radiation have not been related. In this study, the meteorological information of 74 weather stations located in different climates of the country were used to determine the parameters required. The results have been validated with experimental data available for different locations.

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“…There are several methods to do this. Some of the best known are the Angström Turbidity Coefficient and the Linke Factor [28,59,60].…”

Section: Attenuation Processes Of Solar Radiationmentioning

confidence: 99%

Section: Bird and Hulstrom Model And Improvementsmentioning

confidence: 99%

See 1 more Smart Citation

Attenuation processes of solar radiation. Application to the quantification of direct and diffuse solar irradiances on horizontal surfaces in Mexico by means of an overall atmospheric transmittance

Gutiérrez-Trashorras

Villicaña-Ortíz

Álvarez-Álvarez

et al. 2018

Renewable and Sustainable Energy Reviews

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show abstract

“…• the analysis of power spectra and non-linear characteristics of PV power and solar irradiance time series [16,17,32,35,42,43,48,[64][65][66][67][68], • the comparison of power fluctuations from specific PV plants with corresponding irradiance measurements [25,43,57,69], • the characterization of power variability as a function of PV plant size [13,25,36,44], • the assessment of the effects of partial shadowing on performance reduction from single modules to entire PV systems [51,[70][71][72], • the development of methods to infer irradiance and PV power estimates from whole sky images [47,[73][74][75][76][77][78][79][80][81], • the proposition of classification schemes and measures to quantify variability [25,38,39,[82][83][84][85][86][87], • the estimation of spatial smoothing, including correlation structures and decorrelation length scales of irradiance and PV power, as well as their increments…”

Section: Introductionmentioning

confidence: 99%

Irradiance Variability Quantification and Small-Scale Averaging in Space and Time: A Short Review

Lohmann¹

2018

Preprint

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With the continual global increase of PV power systems and the inherent weather-induced volatility of their power output, understanding the underlying variability of solar radiation in both space and time is important for the planning and reliable operation of future power grids. This paper concisely reviews recent advances in the characterization of irradiance variability with an emphasis on small spatial and temporal scales (respectively less than about 10 km and 1 min), for which comprehensive data sets are time consuming and expensive to collect, and although needed have not been available until recently. Special attention is given to studies dealing with the quantification of variability using such unique data, the analysis and modeling of spatial smoothing, and the evaluation of temporal averaging.

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“…Ghonima et al (2012) and Shields et al (2013) give rich and interesting reviews of sky imager systems and their applications. Several algorithms have now been proposed that enable us to retrieve an estimation of cloud cover (e.g., Long and DeLuisi, 1998;Li et al, 2011;Ghonima et al, 2012;Martinis et al, 2013;Silva and Echer, 2013;Cazorla et al, 2015;Kim et al, 2016;Krinitskiy and Sinitsyn, 2016) or solar irradiance (Pfister et al, 2003;Chu et al, 2014;Chauvin et al, 2015;Kurtz and Kleissl, 2017), to classify the type of observed clouds (e.g., Heinle et al, 2010;Kazantzidis et al, 2012;Xia et al, 2015;Gan et al, 2017), or to track them (Peng et al, 2015;Cheng, 2017;Richardson et al, 2017). Sky imagers have also been specifically used for the detection of cirrus or thin clouds (Li et al, 2012) and contrail studies (Schumann et al, 2013).…”

mentioning

confidence: 99%

ELIFAN, an algorithm for the estimation of cloud cover from sky imagers

et al. 2019

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Abstract. In the context of a network of sky cameras installed on atmospheric multi-instrumented sites, we present an algorithm named ELIFAN, which aims to estimate the cloud cover amount from full-sky visible daytime images with a common principle and procedure. ELIFAN was initially developed for a self-made full-sky image system presented in this article and adapted to a set of other systems in the network. It is based on red-to-blue ratio thresholding for the distinction of cloudy and cloud-free pixels of the image and on the use of a cloud-free sky library, without taking account of aerosol loading. Both an absolute (without the use of a cloud-free reference image) and a differential (based on a cloud-free reference image) red-to-blue ratio thresholding are used. An evaluation of the algorithm based on a 1-year-long series of images shows that the proposed algorithm is very convincing for most of the images, with about 97 % of relevance in the process, outside the sunrise and sunset transitions. During those latter periods, however, ELIFAN has large difficulties in appropriately processing the image due to a large difference in color composition and potential confusion between cloud-free and cloudy sky at that time. This issue also impacts the library of cloud-free images. Beside this, the library also reveals some limitations during daytime, with the possible presence of very small and/or thin clouds. However, the latter have only a small impact on the cloud cover estimate. The two thresholding methodologies, the absolute and the differential red-to-blue ratio thresholding processes, agree very well, with departure usually below 8 % except in sunrise–sunset periods and in some specific conditions. The use of the cloud-free image library gives generally better results than the absolute process. It particularly better detects thin cirrus clouds. But the absolute thresholding process turns out to be better sometimes, for example in some cases in which the sun is hidden by a cloud.

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Measuring diffuse, direct, and global irradiance using a sky imager

Cited by 31 publications

References 16 publications

Attenuation processes of solar radiation. Application to the quantification of direct and diffuse solar irradiances on horizontal surfaces in Mexico by means of an overall atmospheric transmittance

Attenuation processes of solar radiation. Application to the quantification of direct and diffuse solar irradiances on horizontal surfaces in Mexico by means of an overall atmospheric transmittance

Irradiance Variability Quantification and Small-Scale Averaging in Space and Time: A Short Review

ELIFAN, an algorithm for the estimation of cloud cover from sky imagers

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