Open Access
Evaluación comparativa de 19 modelos de estimación de irradiancia difusa sobre planos inclinados dependiendo del tipo de cielo estándar ISO/CIE
(LNEG, 2020) García Ruiz, Ignacio; Torres Escribano, José Luis; Blas Corral, María Ángeles de; Sáenz Gamasa, Carlos; Hernández Salueña, Begoña; Illanes, R.; Ingeniería; Ingeniaritza; Ciencias; Zientziak
En este trabajo se han evaluado 19 modelos de estimación de irradiancia difusa sobre el plano inclinado, que incluyen tanto modelos isotrópicos o pseudoisotrópicos como modelos anisotrópicos. Dicha evaluación se ha llevado a cabo a partir una serie de 5396 observaciones de irradiancia global, difusa y directa realizadas entre julio y diciembre de 2018 en la estación radiométrica de la Universidad Pública de Navarra (UPNA). El estado del cielo correspondiente a cada observación se ha caracterizado de acuerdo con el CIE Standard General Sky propuesto en la norma ISO 15469:2004(E)/CIE S 011/E:2003. Para esta clasificación se han utilizado las medidas de distribución angular de luminancia y radiancia proporcionadas por un escáner de cielo ubicado en la propia estación de la UPNA. De tal manera que, para cada combinación de orientación e inclinación del plano, se ha evaluado la bondad de los distintos modelos de acuerdo con los 15 tipos de cielo estándar propuestos por la norma ISO/CIE. Los resultados revelan que el modelo de Perez et al. 2 presenta los mejores resultados globales, así como en 5 de los 15 tipos de cielo ISO/CIE.
Open Access
Analytical expressions for estimating sky diffuse irradiance and illuminance on tilted planes for the CIE standard general skies
(Elsevier, 2021) Torres Escribano, José Luis; García Ruiz, Ignacio; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
This work proposes a set of analytical expressions for the calculation of the relationship between sky diffuse illuminance on a tilted plane and horizontal plane corresponding to the 15 ISO/CIE standard sky types. Given the parallelism in the angular distribution of sky diffuse radiance and luminance, these expressions can also be used to calculate the diffuse sky irradiance on an inclined plane. The proposed analytical expressions are obtained by adjusting the results of a numerical calculation whose methodology is described in detail in the paper. The use of these analytical expressions significantly reduces the calculation time. It is verified that the relative root-mean-square errors obtained with the analytical expressions are small compared with the use of numerical calculation, ranging from 0.03% to 4.09%, and with a tendency to increase with clear skies and high solar zenith angles.
Open Access
A GIS-based methodology for assigning experimental measurements of angular distribution of sky radiance and luminance to selected sky sectors
(Elsevier, 2019) García Ruiz, Ignacio; García Gorostiaga, M. Almudena; Torres Escribano, José Luis; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
Mathematical models for the estimation of the angular distribution of diffuse radiance/luminance in the sky describe the anisotropic character of diffuse solar radiation and daylight in the sky vault. In most of these models the radiance/luminance of a sky point is determined by the product of the indicatrix function and the gradation function. When developing and/or calibrating these models, it is typical to consider separately the dispersion effects in the direction of the sun's rays and the gradation from the zenith towards the horizon. To do this, the sky is divided into a number of concentric spherical zones around the sun and a number of concentric spherical zones around the zenith. The intersection between both sets of zones delimits a series of sky elements. Unfortunately, these sky elements do not correspond to the 145 patches of sky vault recommended by the International Commission on Illumination (CIE), which are routinely scanned by the existing commercial sky scanners. The identification of the sky elements, geometrically different from those observed by commercial sky scanners, and the assignation of the radiance/luminance values registered by such sky scanners are not analytically trivial tasks. A GISbased methodology is presented in this work to undertake these goals.
Open Access
Estimation of the solar thermal power generation potential in Pamplona (northern Spain)
(Universidad Carlos III, 2022) García Ruiz, Ignacio; Prieto Cobo, Eduardo; Torres Escribano, José Luis; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
In this work, an analysis of the potential of the city of Pamplona to produce solar thermal energy was carried out, according to the solar radiation received. As a result, for each residential, industrial, or service rooftop, information was provided on (1) the area available for thermal installation, (2) the solar thermal installation capacity and (3) the monthly and annual thermal energy generation potential. It was found that, if all suitable areas of the city are used, it would be possible to achieve an annual total solar thermal energy production of 1197.69 GWh. If solar energy supply and thermal demand were perfectly coupled over time, it would be possible to cover 99.1% of Pamplona's thermal energy demand.
Open Access
Luminance calibration of a full sky HDR imaging system using sky scanner measurements
(Solar Energy Society, 2022) García Ruiz, Ignacio; Sáenz Gamasa, Carlos; Hernández Salueña, Begoña; García Santos, Rafael; Torres Escribano, José Luis; Zientziak; Ingeniaritza; Institute of Smart Cities - ISC; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Ingeniería
A full sky High Dynamic Range imaging system, based on a Single-Lens Reflex camera with a fisheye lens, has been constructed and calibrated with a sky scanner luminance meter. The method considers the geometrical, spectral, timing and orientation issues between instruments. The calibration data sets, having nearly simultaneous measurements under stable sky conditions, were obtained from approximately one month of data using selection variables based in the experimental design. For luminance estimation we use the standard 𝐶𝐼𝐸𝑌 RGB combination and a Spectrally Matched Luminance (𝑆𝑀𝐿) predictor, matching the spectral response of the instruments. With 738 calibration points having luminances up to 23.6 kcd∕m2, covering 98.5% of the sky luminance range, 𝐶𝐼𝐸𝑌 is linearly correlated with sky scanner measurements with a coefficient of determination 𝑅2 = 0.9927 and a Root Mean Squared Error (𝑅𝑀𝑆𝐸) of 7.7%. 𝑆𝑀𝐿 gives better results, with 𝑅2 = 0.9973 and 𝑅𝑀𝑆𝐸 = 5.3%. With 253 calibration points with luminances up to 12.9 kcd∕m2, comprising 94.1% of the sky luminance range, both predictors clearly improve, with 𝑅2 = 0.9964 and 𝑅𝑀𝑆𝐸 = 4.1% in case of 𝐶𝐼𝐸𝑌 and 𝑅2 = 0.9982 and 𝑅𝑀𝑆𝐸 = 2.9% in case of 𝑆𝑀𝐿.
Open Access
Proposal and evaluation of typical illuminance year (TIY) generation procedures from illuminance or irradiance data for daylight assessment in the long term
(Elsevier, 2020) García Ruiz, Ignacio; Blas Corral, María Ángeles de; Torres Escribano, José Luis; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
When assessing the long-term daylight availability or the performance of natural lighting systems in a given location, it is necessary to have representative data of local daylight conditions. The use of a daylight test reference year (TRY) becomes a good option in these cases. This paper proposes and evaluates a procedure for the generation of a typical illuminance year (TIY) considering illuminance as the only variable for selecting the typical periods that make up the reference year. Two versions of TIY are presented, one composed of 12 typical months selected from the series of observations and another composed of 365 typical days. Each of these versions is used to obtain a global illuminance TIY (TGIY) and a diffuse illuminance TIY (TDIY) from a 27-year dataset corresponding to the Vaulx-en-Velin station (France). Furthermore, 12 luminous efficacy models have been evaluated in order to obtain a TIY from a TRY generated from irradiance data when no illuminance data are available. Thus, a global luminous efficacy model and a diffuse model are selected after benchmarking different models, considering both their original coefficients and those adjusted to local conditions. The results reveal that the monthly version of the TGIY and the daily version of the TDIY show the best overall fit to the long-term dataset. TIYs obtained from illuminance data are also observed to be statistically indistinguishable from those obtained after applying a luminous efficacy model to an irradiance-based TRY.
Open Access
Calculation of intercepted photosynthetically active radiation (IPAR) for traditional crops in Castilla y León, Spain
(Universidad Carlos III, 2022) Garrachón-Gómez, Elena; García Ruiz, Ignacio; García-Rodríguez, Ana; García-Rodríguez, Sol; Alonso-Tristán, Cristina; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
Agriculture is one of the most important economic activities in the Castilla y León region (Spain), approximately one-third of the land area is destined for this use. The role of agriculture in rural areas is essential from a territorial perspective, where rural depopulation is originating a crisis in the countryside. Moreover, climate change is having a major impact on agricultural productivity as a consequence, among others, of the increase in the frequency and the severity of extreme events, especially in Mediterranean regions [1]. For these reasons, it is essential to highlight the vision of agriculture as a multifunctional activity. Besides good management, productivity depends on many other factors, such as soil properties or climatic factors. A decisive climatic variable, which is often not considered in the planning and management of the crops, is the Photosynthetically Active Radiation (PAR), specifically, the Intercepted Photosynthetically Active Radiation (IPAR). The main purpose of this study is to calculate and represent an estimation of IPAR values for the most characteristic crops of Castilla y León.
Open Access
Generation of the site-adapted clearest-sky year of direct normal irradiance for solar concentrating technologies
(Elsevier, 2018) García Ruiz, Ignacio; Royo Romeo, Alberto; Torres Escribano, José Luis; Proyectos e Ingeniería Rural; Landa Ingeniaritza eta Proiektuak; Gobierno de Navarra / Nafarroako Gobernua
Concentrating photovoltaic and thermoelectric solar facilities base their operation on collecting the direct component of solar radiation. Given that the direct beam that reaches the Earth's surface varies greatly in time and space, it is common to assist the bankability of projects with a solar resource assessment. Sun-tracking collector plants are typically examined via a time series analysis of measured weather data and test reference years. Such analysis, which considers the eventual presence of clouds, may be complemented with the use of the synthetic clear-sky year assuring the maximum theoretical availability of direct normal irradiance at a site. This work introduces for the first time the concept of siteadapted clearest-sky year (CSY) and provides a methodology for its generation. Three methods to build the CSY and one algorithm to detect clear-sky moments are proposed.
Open Access
Photovoltaic prediction software: evaluation with real data from Northern Spain
(MDPI, 2021) González Peña, David; García Ruiz, Ignacio; Díez-Mediavilla, Montserrat; Dieste-Velasco, María Isabel; Alonso-Tristán, Cristina; Ingeniería; Ingeniaritza
Prediction of energy production is crucial for the design and installation of PV plants. In this study, five free and commercial software tools to predict photovoltaic energy production are evaluated: RETScreen, Solar Advisor Model (SAM), PVGIS, PVSyst, and PV*SOL. The evaluation involves a comparison of monthly and annually predicted data on energy supplied to the national grid with real field data collected from three real PV plants. All the systems, located in Castile and Leon (Spain), have three different tilting systems: fixed mounting, horizontal-axis tracking, and dual-axis tracking. The last 12 years of operating data, from 2008 to 2020, are used in the evaluation. Although the commercial software tools were easier to use and their installations could be described in detail, their results were not appreciably superior. In annual global terms, the results hid poor estimations throughout the year, where overestimations were compensated by underestimated results. This fact was reflected in the monthly results: the software yielded overestimates during the colder months, while the models showed better estimates during the warmer months. In most studies, the deviation was below 10% when the annual results were analyzed. The accuracy of the software was also reduced when the complexity of the dual-axis solar tracking systems replaced the fixed installation.
Open Access
The sky characterization according to the CIE Standard General Sky: comparative analysis of three classification methods
(Elsevier, 2020) García Ruiz, Ignacio; Blas Corral, María Ángeles de; Torres Escribano, José Luis; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Since the publication of the standard sky luminance distributions (SSLD) that was consolidated in the ISO 15469:2004(E)/CIE S 011/E:2003, numerous procedures have emerged for the characterization of the sky condition according to that standard. Precisely, the use of different procedures for the classification of the skies of a certain place according to the ISO/CIE standard can lead to obtain different frequencies of sky types. The existing uncertainties in the characterization of the sky condition according to the CIE Standard General Sky as a consequence of the classification procedure used are analyzed in this study. For this, three different classification procedures are used to characterize the sky radiance and luminance distribution measurements made by means of a sky-scanner in Pamplona (Spain) from 2007 to 2013. That is, (1) a method focused on determining the relative gradation and indicatrix functions, (2) a method based on the comparison of measured and standard luminances normalized against the horizontal diffuse illuminance, and (3) a new high-spatial-resolution approach that compares measured and standard luminances relative to zenith. In general terms, it is concluded that there is some uncertainty in the classification depending on the procedure used to characterize the sky.