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Dive into the research topics where F.J. Batlles is active.

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Featured researches published by F.J. Batlles.


Solar Energy | 1995

On shadowband correction methods for diffuse irradiance measurements

F.J. Batlles; F.J. Olmo; L. Alados-Arboledas

Abstract Diffuse irradiance, G d , is an important variable in solar resource assessment. The diffuse irradiance can be worked out from global, G , and direct, G b , irradiance measurements, but this method involves the use of relatively expensive tracking mechanisms. Alternatively, a widely accepted technique uses a pyranometer with a shadowband. Because the shadowband screens the sensor from part of the diffuse radiation coming in from the sky, a correction must be made to the measurements. However, because of the anisotropy of diffuse radiation it is difficult to compute an exact theoretical correction. In this study we use two data sets registered in two locations in Spain. The first one consists in coincident hourly values of global, direct, and diffuse irradiance; the latter by means of shadowband. The other data set includes the same variables but as 5-minute values. Our goal is to study the necessary correction factor for diffuse irradiance measurements obtained by means of shadowband. After testing several well-known correction methods, we have developed two different correction models, using two-thirds of the hourly data set, while the remaining one-third and the whole 5-minute data set have been used for validation purposes. The last validation test suggests that our anisotropic models provide reliable corrections for conditions different than the ones where they have been developed. The results obtained by the developed models show a negligible mean bias deviation. Approximately 55% of cases present deviations lower than 5% over the mean value of diffuse irradiance.


Agricultural and Forest Meteorology | 2001

Estimation of hourly global photosynthetically active radiation using artificial neural network models

G. López; Miguel Angel Rubio; M. Martı́nez; F.J. Batlles

Abstract Photosynthetically active radiation (PAR) reaching the earth’s surface is a major parameter controlling many biological and physical processes related with the evolution of plant canopies, agricultural and environmental fields. Unfortunately, PAR is not often measured and therefore it must be estimated. The unavailability of measurements of global solar radiation at the place of interest and different factors affecting the linear relation between PAR and global solar radiation can preclude the estimation of PAR from global solar radiation. In this paper, a novel approach based on a simple multilayered feedforward perceptron has been used to analyse the non-linear relationships between PAR and different meteorological and radiometric variables in order to determine their relative relevance. An artificial neural network based model for the estimation of the hourly PAR involving hourly global irradiance as only measured variable has been successfully developed. The model was tested using data recorded at six radiometric stations covering a wide range of climates. The model performance has been compared with other existing empirical complex models showing important improvements. Next, a second artificial neural network based model involving only sunshine duration measurements has been developed and proved to be an acceptable alternative to calculate hourly PAR when radiometric information is not available.


Energy | 2000

Empirical modeling of hourly direct irradiance by means of hourly global irradiance

F.J. Batlles; M.A. Rubio; J. Tovar; F.J. Olmo; L. Alados-Arboledas

A very important factor in the assessment of solar energy resources is the availability of direct irradiance data of high quality. Nevertheless, this quantity is seldom measured and thus must be estimated from measures of global solar irradiance, a quantity that is registered in most radiometric stations. In this work we analyze the results provided by different models in the estimation of hourly direct irradiance values. We have selected several models proposed by Orgill and Hollands, Erbs et al., Reindl et al., Skarveit and Olseth, Maxwell, and Louche et al. With the exception of the model from Louche et al. that estimates direct irradiance values from direct transmittance values, all of the models estimate direct irradiance from the diffuse fraction. The data set used in this study comprises 25 000 hourly values of global and diffuse irradiance. These values were registered in six Spanish locations with different climatic conditions. The results provided by the model depend on the clearness index, kt, and the solar elevation. The best results are obtained for cloudless skies and higher solar elevation. In those conditions we can estimate the direct irradiance with a root square mean error close to 14% of the average measured value. We have estimated the direct irradiance under cloudless sky conditions using a parametric model proposed by Iqbal. In order to analyze the effect of turbidity on the estimation of direct irradiance we have compared the results obtained by the parametric model when using hourly values of the Angstrom turbidity parameter β with those obtained when using monthly means of hourly values of β.


Energy | 2001

Dependence of one-minute global irradiance probability density distributions on hourly irradiation

J. Tovar; F.J. Olmo; F.J. Batlles; L. Alados-Arboledas

This paper analyzes the behavior of one minute global irradiance distributions as a function of hourly average solar global irradiance. For this purpose, we have used the clearness index kt which describes the atmospheric transmittance. Our interest is in characterizing the intrahourly variability of solar global irradiance and the behavior of the instantaneous values as a function of hourly values of solar global irradiance. The distributions are unimodal and show a marked symmetry around a central value that is close to the corresponding hourly average value. The probability density functions have been modeled using functions based on the Boltzmann statistic used in recent studies of the one minute distributions of kt conditioned to the optical air mass. These functions provide good fit of the distributions and are analytically integrable and can be inverted analytically. The one minute global irradiance data used in this study have been recorded during a three year period in a radiometric station located in south eastern Spain.


Solar Energy | 1995

Solar radiation resource assessment by means of silicon cells

L. Alados-Arboledas; F.J. Batlles; F.J. Olmo

Abstract 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 Almeria, 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.


Solar Energy | 1999

ONE MINUTE kb AND kd PROBABILITY DENSITY DISTRIBUTIONS CONDITIONED TO THE OPTICAL AIR MASS

J. Tovar; F.J. Olmo; F.J. Batlles; L. Alados-Arboledas

In this work we have analysed and modelled one-minute probability distribution function of solar direct and diffuse irradiance conditioned to the optical air mass. For this purpose, we have used one-minute data acquired in a radiometric station located in southeastern Spain (37.13° N, 3.63° W, 687 m a.m.s.l.). The study has been made over the dimensionless indices kb and kd. We have found marked bimodality in the kb distribution function and asymmetry associated with the unimodal function of one-minute kd values. In spite of these differences, we have modelled both distribution functions using a functional form based on Botlzmanns statistics. These functions have been used in a previous study devoted to modelling the clearness index for global radiation, kt. In order to model the asymmetry that is evident in the kd and kb distribution functions, the functional forms have been modified by the inclusion of an additional parameter. The adjustable parameters included in the model equations present a dependence on the optical air mass.


Renewable Energy | 2000

Estimation of hourly direct normal from measured global solar irradiance in Spain

Gabriel López; Miguel Angel Rubio; F.J. Batlles

The availability of a good data set, registered in six Spanish locations, including several radiometric variables, has been used to test different approaches for estimating hourly direct normal irradiance by decomposition models. Models proposed by different authors have been tested. Following this preliminary study, to improve the kb–kt correlations, another geometric variable has been used as a predictor of hourly beam transmittance, kb, by means of piecewise correlations. The new beam transmittance correlations, which include additional geometric information, reduce the root mean square deviation. In addition, they show a better performance in terms of the determination coefficient of the regression analysis of measured vs calculated values, providing an improved capture of the real world effects than models that are function of the clearness index only. A new model that uses only two ranges of clearness index is proposed. The proposed model shows seasonal dependence and thus we have developed a seasonal version of it. However, the performance of the seasonal version has proved to be similar to the corresponding annual model.


Environmental Science & Technology | 2010

Environmental assessment of the CIESOL solar building after two years operation.

F.J. Batlles; S. Rosiek; Ivan Muñoz; Amadeo R. Fernández-Alba

Life cycle assessment is applied to assess the environmental benefits and trade-offs of a solar-assisted heating, ventilating, and air-conditioning (HVAC) system installed in the CIESOL building in Almeria (southeastern Spain). The environmental performance of this system is compared to that of a conventional HVAC system using a heat pump. The study evaluates these systems from cradle to grave, and the impact assessment includes, in addition to the CML2001 method, an impact category dealing with impacts on freshwater resources. The results show that the solar-assisted HVAC involves lower impacts in many impact categories, achieving, as an example, a reduction of 80% in greenhouse-gas emissions. On the other hand, key weak points of this system are the production of capital goods, but specially water use for cooling, due to its high impact on freshwater resources. Minimization of water requirements should be a priority for further development of this promising technology.


Solar Energy | 1996

Performance of global to direct/diffuse decomposition models before and after the eruption of Mt. Pinatubo, June 1991

F.J. Olmo; F.J. Batlles; L. Alados-Arboledas

Different decomposition models have been developed to estimate hourly direct and diffuse solar irradiance from hourly global irradiance measurements. Besides clearness index kt, other geometric and meteorological variables have been tested as predictors of hourly diffuse fraction, k, or hourly beam transmittance index, kb, by means of piecewise correlations. The recent volcanic eruption of Mount Pinatubo (June 1991) was responsible for important modifications in the solar radiation fluxes. In this article we address the effect of the volcanic aerosols on the performance of some well-known empirical models, using a data set including different radiometric and meteorological variables. The study has revealed that the more pronounced performance changes affected the higher kt intervals associated with the lower levels of cloud cover. After the eruption, all the models present a general tendency to overestimate the direct component and underestimate the diffuse component.


Energy | 2004

Selection of input parameters to model direct solar irradiance by using artificial neural networks

Gabriel López; F.J. Batlles; J. Tovar-Pescador

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S. Rosiek

University of Almería

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F.J. Olmo

University of Granada

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J.L. Bosch

University of Almería

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J. Alonso

University of Almería

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J. Polo

United States Department of Energy

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