Values Of Global Solar Radiation Research Articles

Prediction of global solar radiation using support vector machines

ABSTRACTThis article utilizes Support Vector Machines (SVM) for predicting global solar radiation (GSR) for Sharurha, a city in the southwest of Saudi Arabia. The SVM model was trained using measured air temperature and relative humidity. Measured data of 1812 values for the period from 1998–2002 were obtained. The measurement data of 1600 were used for training the SVM, and the remaining 212 were used for comparison between the measured and predicted values of GSR. The GSR values were predicted using the following four combinations of data sets: (i) Daily mean air temperature and day of the year as inputs, and global solar radiation as output; (ii) daily maximum air temperature and day of the year as inputs, and GSR as output; (iii) daily mean air temperature and relative humidity and day of the year as inputs, and GSR as output; and (iv) daily mean air temperature, day of the year, relative humidity, and previous day’s GSR as inputs, and GSR as output. The mean square error was found to be 0.0027, 0.0023, 0.0021, and 7.65 × 10−4 for case (i), (ii,), (iii), and (iv) respectively, while the corresponding absolute mean percentage errors were 5.64, 5.08, 4.48, and 2.8%. Obtained results show that the SVM method is capable of predicting GSR from measured values of temperature and relative humidity.

Performance assessment of different day-of-the-year-based models for estimating global solar radiation - Case study: Egypt

Different models are introduced to predict the daily global solar radiation in different locations but there is no specific model based on the day of the year is proposed for many locations around the world. In this study, more than 20 years of measured data for daily global solar radiation on a horizontal surface are used to develop and validate seven models to estimate the daily global solar radiation by day of the year for ten cities around Egypt as a case study. Moreover, the generalization capability for the best models is examined all over the country. The regression analysis is employed to calculate the coefficients of different suggested models. The statistical indicators namely, RMSE, MABE, MAPE, r and R2 are calculated to evaluate the performance of the developed models. Based on the validation with the available data, the results show that the hybrid sine and cosine wave model and 4th order polynomial model have the best performance among other suggested models. Consequently, these two models coupled with suitable coefficients can be used for estimating the daily global solar radiation on a horizontal surface for each city, and also for all the locations around the studied region. It is believed that the established models in this work are applicable and significant for quick estimation for the average daily global solar radiation on a horizontal surface with higher accuracy. The values of global solar radiation generated by this approach can be utilized in the design and estimation of the performance of different solar applications.

Global, diffuse and direct solar radiation at the surface in the city of Rio de Janeiro: Observational characterization and empirical modeling

The city of Rio de Janeiro and others 18 cities compose the Metropolitan Area of Rio de Janeiro. The main objective of this work is to characterize observationally the diurnal and seasonal evolution of the solar radiation components in the city of Rio de Janeiro. The measurements of global and diffuse solar radiation and standard meteorological variables at the surface have been carried out regularly at the Geoscience Institute of Federal University of Rio de Janeiro since October of 2011. The microclimatic conditions show that the period 2011–2014 was warmer during most of the year and drier in summer and spring in comparison with climate normal. All solar radiation components present a well defined diurnal cycle with maximum at noon. The estimates of global and direct solar radiation indicate a great potential available for solar energy at the surface, particularly in summer. The behavior of the clearness index and diffuse solar radiation fraction is similar in summer and winter. The Angstrom formula represents properly the estimate of the monthly average daily value of global solar radiation. The sigmoid logistic function is statistically more significant in comparison with others correlation models to represent the diffuse fraction as a function clearness index.

Performance Investigation of the Solar Chimney Power Plants Heater Case Study in Aswan, Egypt

Solar collector is a thermal device that uses the heated air in the power generation and many engineering applications. The purpose of the present work is to study the performance and temperature distribution for the solar collector which uses heated air in solar chimney power generation that it consist of three parts, a turbine-generator unit which is used in the generation of electric energy, and cylindrical chimney is fixed vertically and finally a solar collector under the climatic conditions of Egypt-Aswan is studied. This site is specified as the hottest site because the nearest of this location from the Tropic of cancer. Experiments are performed in ten summer days of May and June 2015 with different solar radiations and clarity of the sky. Hourly values of global solar radiation and some meteorological data (temperature, pressure, velocity, etc.) for measuring days are obtained by measuring devices. Inlet and outlet temperatures of air from a solar collector and velocity at junction region. In this work, attempt has been made to present the effect of environmental factors such as ambient temperature, the clarity of the sky and solar radiation on the performance of solar collector. The temperature of the base and the cover of the solar collector, the variation of solar radiation, solar collector efficiency, heat transfer coefficient, the velocity at the junction region between the chimney base, the outlet of the solar collector and temperature distribution along the air heater are discussed. A prediction for the results of the solar collector were performed by using developed theoretical model was made by this study which is based on the previous works. The numerical study has used a commercial code CFX, ANSYS 16.1 to simulate the flow through the collector. The study show that the outlet air temperatures from the solar collector and the velocity at the junction are depending on the climate condition such as ambient temperature and solar radiation, the differences in air temperature at the solar collector ranging between 8° - 24°. It is concluded that the theoretical model is basically valid for the system under study, and theCFD simulation can be used conveniently to predict the performance of the system, the comparison between them and experimental result shows a good agreement.

Estimation of monthly global solar radiation in the eastern Mediterranean region in Turkey by using artificial neural networks

In this study, an artificial neural network (ANN) model was used to estimate monthly average global solar radiation on a horizontal surface for selected 5 locations in Mediterranean region for period of 18 years (1993-2010). Meteorological and geographical data were taken from Turkish State Meteorological Service. The ANN architecture designed is a feed-forward back-propagation model with one-hidden layer containing 21 neurons with hyperbolic tangent sigmoid as the transfer function and one output layer utilized a linear transfer function (purelin). The training algorithm used in ANN model was the Levenberg Marquand back propagation algorith (trainlm). Results obtained from ANN model were compared with measured meteorological values by using statistical methods. A correlation coefficient of 97.97 (~98%) was obtained with root mean square error (RMSE) of 0.852 MJ/m2 , mean square error (MSE) of 0.725 MJ/m2 , mean absolute bias error (MABE) 10.659MJ/m2 , and mean absolute percentage error (MAPE) of 4.8%. Results show good agreement between the estimated and measured values of global solar radiation. We suggest that the developed ANN model can be used to predict solar radiation another location and conditions.

Global solar radiation estimation using artificial neural network by the addition of nearby meteorological stations' solar radiation data and exergy of solar radiation: a case study

The artificial neural networks (ANNs) can be used to accurately predict the global solar radiation (GSR). There are many geographical, meteorological and terrestrial parameters affecting GSR. In this study, the most relevant of six input parameters are selected to predict the GSR of Goksun Station in Turkey using Waikato environment for knowledge analysis (Weka) Software. The effect of using nearby meteorological stations' GSR data as input on GSR prediction is investigated. Different ANN models are developed to demonstrate the difference between the exclusion and inclusion of these parameters on the model. The results show that the exclusion of less influential parameters and the inclusion of three nearby stations' GSR data has improved performance criteria. Petela, Spanner and Jeter's approaches are used for exergy analysis of measured and estimated GSR values. The mean exergy-to-energy ratio for both Petela and Spanner's approaches is 0.934, while Jeter's approach showed 0.950.

Estimation of GSR to ascertain solar electricity cost in context of deregulated electricity markets

Solar energy is the most preferred among the other renewable energies throughout the world. The cost of Solar Electricity plays key role in deregulated Electricity Markets which gets affected by Global Solar Radiation (GSR). In this research, an integrated technique is used to estimate the mean monthly GSR for the four summer months over 14 Indian cities. The goal of this research work is to extract a significant training data set of the several environmental parameters, used for estimating the GSR through the application of Principal Component Analysis (PCA). Further an estimation of the mean monthly GSR will be completed using the significant training data set through the application of Artificial Neural Networks (ANNs). A multi layered, feed forward, standard ANN is considered in estimating the GSR. The performance of ANN was evaluated while it was combined with the statistical technique by calculating the error between estimated and measured values of GSR. Results show that the proposed model estimates GSR with less error and more appropriate than the other empirical models. This study gives a judgment for engineers and researchers on the installation of solar plants at the best suitable places and helps in minimizing the energy crisis in India.

Uso de tela termorrefletora em ambientes protegidos para cultivo do tomateiro

O emprego de telas termorrefletoras, como forma de limitar o aumento da temperatura do ar em ambientes protegidos, deve ser manejado, a fim de evitar a redução excessiva da radiação solar, dada sua importância sobre o desenvolvimento e a produção de hortaliças como o tomateiro. Nesse contexto, os objetivos do trabalho foram comparar os microclimas entre ambientes protegidos cultivados com tomateiro, sendo um coberto somente com polietileno de baixa densidade (PEBD) reforçado e outro coberto com PEBD reforçado associado a uma tela termorrefletora aluminizada retrátil, sob condições de manejo, e avaliar sua adequação às condições climáticas recomendadas à cultura do tomateiro pela bibliografia consultada. O experimento foi conduzido no município de Rio das Pedras-SP, entre 1º-08-11 e 21-01-12. A tela termorrefletora foi empregada somente em dias de céu límpido, entre as 11h e as 16h. Foram coletados dados de temperatura e umidade relativa do ar, radiação solar global (Qs) e radiação fotossinteticamente ativa (RFA) no interior de ambos os ambientes protegidos, e dados de temperatura do ar no ambiente externo. O emprego da tela termorrefletora aluminizada reduziu significativamente os valores médios de Qs, RFA e a temperatura do ar, ao passo que elevou os valores de umidade relativa do ar. O microclima do ambiente com tela adaptou-se melhor às condições climáticas consideradas adequadas pela bibliografia para o cultivo do tomateiro.

An improved method for estimating the Ångström turbidity coefficient β in Central China during 1961–2010

The accurate determination of the atmospheric turbidity is of great importance for atmospheric environment, solar energy applications and climate change studies. Daily values of horizontal direct, diffuse and global solar radiation at Wuhan, Central China during 1961–2010 are used for estimating the monthly mean Ångström turbidity coefficient β. The YHM and YHM2 (Yang hybrid models) are first used to estimate the direct and diffuse components considering the transmittances of ozone, water vapor, gas mixture, aerosol and Rayleigh effect in the radiative transfer processes. An IMW (improved model for Wuhan) is also proposed by combining the format of YHM model with the corrected spectral terms of YHM2 model. Then, the β value can be estimated by varying the estimated direct irradiation until it matches the observation. The model performance is analyzed and compared and further validated by measured values using Sun photometer CE318. It is shown that the IMW model presents more accurate estimates than YHM and YHM2 ones; it is therefore a useful tool for studying the variability and evolution of atmospheric turbidity in other places around the world.

Effects of air pollution for estimating global solar radiation in India

Solar energy is the primary resource for all biological, chemical and physical processes. The amount of global solar radiation is an important parameter for solar energy applications. It is common to estimate a monthly average of daily global solar radiation using different regression models. These models in turn exploit the correlation between solar radiation and various atmospheric factors. These factors are commonly derived from meteorological, geographical and climatological data that are readily available for majority of weather stations across the world. In this paper, a novel regression model that can predict location-independent daily global solar radiation is presented. The proposed exponential quadratic model captures the correlation between measured global solar radiation values, sunshine hour and Air Pollution Index for Indian cities. In addition to this, an extended study of several other regression models (e.g. linear, quadratic, exp.-linear and exp.-quadratic) is also presented. This analysis with real data from Indian cities suggests that air pollution is a more significant factor than location when predicting solar radiation. Finally, the model parameters (regression coefficients) for each model are listed out. Additionally, the generalised model equation for the best performing model is also presented.

Influence of complex topography on global solar radiation in the Yangtze River Basin

Global solar radiation (GSR) is the most direct source and form of global energy, and calculation of its quantity is highly complex due to influences of local topography and terrain inter-shielding. Digital elevation model (DEM) data as a representation of the complex terrain and multiplicity condition produces a series of topographic factors (e.g. slope, aspect, etc.). Based on 1 km resolution DEM data, meteorological observations and NOAA-AVHRR remote sensing data, a distributed model for the calculation of GSR over rugged terrain within the Yangtze River Basin has been developed. The overarching model permits calculation of astronomical solar radiation for rugged topography and comprises a distributed direct solar radiation model, a distributed diffuse radiation model and a distributed terrain reflectance radiation model. Using the developed model, a quantitative simulation of the GSR space distribution and visualization has been undertaken, with results subsequently analyzed with respect to locality and terrain. Analyses suggest that GSR magnitude is seasonally affected, while the degree of influence was found to increase in concurrence with increasing altitude. Moreover, GSR magnitude exhibited clear spatial variation with respect to the dominant local aspect; GSR values associated with the sunny southern slopes were significantly greater than those associated with shaded slopes. Error analysis indicates a mean absolute error of 12.983 MJm−2 and a mean relative error of 3.608%, while the results based on a site authentication procedure display an absolute error of 22.621 MJm−2 and a relative error of 4.626%.

Validation study of an overall radiation balance estimation method under Ponta Grossa (PR) Brazil weather conditions

Radiation balance is the fraction of incident solar radiation upon earth surface which is available to be used in several natural processes, such as biological metabolism, water loss by vegetated surfaces, variation of temperature in farming systems and organic decomposition. The present study aimed to assess and validate the performance of two estimation models for Rn in Ponta Grossa city, Paraná State, Brazil. To this end, during the period of 04/01/2008 to 04/30/2011, from radiometric data collected by an automatic weather station set at the Experimental Station, of the State University of Ponta Grossa. We performed a linear regression study by confrontation between measurements made through radiometric balance and Rn estimates obtained from Brunt classical method, and the proposed method. Both models showed excellent performance and were confirmed by the statistical parameters applied. However, the alternative method has the advantage of requiring only global solar radiation values, temperature, and relative humidity.

Evaluation of the Hourly Global Solar Radiation on a Horizontal Plane for Two Sites in Algeria

We present three models for the estimation of hourly global solar radiation for two sites in Algeria, namely: Djelfa (Latitude 34.68°N, Longitude 3.25°E, Altitude 1126 (m)) and Ain Bessem (Latitude 36.31°N, Longitude 3.67°E, Altitude 629 (m)). The models are: the Gaussian distribution model, the model by Collares-Pereira-RabI and the H.A. model (Hourly absolute modelling approach). The experimental assessment was done using recorded values of the hourly global solar radiation on a horizontal plane during the period 2000-2004. The obtained results show a close similarity between the solar radiation values calculated by the three models and the measured values, especially for the first model. The experimental validation shows promising results for the estimation and precise prediction of the hourly global solar radiation.

Heat transfer coefficient and thermal losses of solar collector and Nusselt number correlation for rectangular solar air heater duct with longitudinal fins hold under the absorber plate

An experimental investigation has been carried out for a series of system and operating parameters in order to analyze the effect of mass flow rate on heat transfer and Nusselt number characteristics in solar air heater. Experiments are performed at different air mass flow rates; varying from 0.012 to 0.016 kg/s, about hot summer days of Mai 2012. Hourly values of global solar radiation and some meteorological data (temperature, wind speed, relative humidities, etc.) for measuring days are obtained from the Biskra city of Algeria. The experiments encompassed the flow Reynolds number in the range 965.48–1301.4. Longitudinal fins were used inferior the absorber plate for an increase the heat exchange and render the flow fluid in the channel uniform. The effects of mass flow rate of air on the outlet temperature, Nusselt Number, Reynolds Number, Prandtl Number, the heat transfer in the thickness and length of the solar air collector were studied. For this effect was have created a new correlation correspondent of solar air collector with using fins it was written Nu = κ0Re1.36Pr−0.68exp(0.342m)h[−0.018Pr].

Global Solar Radiation of Some Regions of Cameroon Using the Linear Angstrom and Non-Linear Polynomial Relations (Part I) Model Development

The aim of this paper is to evaluate the global solar radiation of some representative cities of Cameroon using the linear Angstrom and non-linear polynomial relations. The choice of these cities which include: Bamenda in the North West region, Douala in the littoral region, Yaounde in the centre region, Ngaoundere in the Adamawa region, and Bertoua in the eastern region; is determined mostly by the availability of data. The Angstrom correlation coefficients for the linear, quadratic and cubic polynomial models would be calculated using the least square method for the different regions. The input data for the analyses are the measured global solar radiation and mean number of monthly sun shine hours. The data for the analyses is obtained partly from the archives of National Aeronautics and Space Administration (NASA) and partly from the archives of the Cameroon Department of Meteorology, Douala. The data used covers a period of 23 years from 1983 to 2005. We demonstrate the validity of the developed models by comparing the evaluated values of global solar radiation with the measured ones. Hence the regression equations can be used to confidently predict the global solar radiation of the representative regions in the absence of experimental data.

Evaluation of clear-sky conditions in high altitude sites

The correct assessment of cloud conditions in any site is important for determining the characteristics of solar resource availability. The criterion proposed by Iqbal has been widely used for this purpose, through the classification of the daily clearness index Kt. However, evidence was found to suggest that this criterion may not be applicable to data measured in high altitude sites, because partially cloudy days are incorrectly classified as clear-sky days. This paper analyzes the cloudiness state of the sky by observing the values of the clearness index Kt and the clear-sky index Kc. These indices were obtained from reliable global solar irradiance data measured over a year in three places of Argentina located at different altitudes (25, 1200 and 3700 m.a.s.l). ESRA and ARG-P models were used to estimate daily clear-sky global solar irradiation values Hc. They also reveal that the most probable value of Kc which corresponds to an actual clear-sky day of a particular location and time depends on the model used to estimate the clear-sky global solar radiation values. Thus, it was confirmed that, unlike the index Kc, the Iqbal's criterion does not correctly classify the cloud cover status from data measured in high altitude sites (>1000 m.a.s.l.).

Statistical analysis of solar UVB and global radiation in Kuwait

An outdoor test facility is installed at the College of Technological Studies, Kuwait for continuous measurements of solar UVB radiation, solar global radiation, relative humidity in Kuwait for two years in the period from 1st June 2010 till 31st May 2012. It is found that the variation of diurnal UVB and global radiation with time of the day almost follows the same trend for all measured clear days. Regression analysis is adapted to establish a mathematical formula relating UVB radiation to both the global solar radiation and relative humidity. The statistical analysis of the present results revealed that there is strong relationship between UVB radiation and both global solar radiation and relative humidity, particularly in the region of moderate to low global solar radiation values. The value of UV (ultraviolet) index which is a measure of the UV radiation level at the Earth's surface is determined at different months through the day hours. The highest UV index values are achieved through the months May–August during the midday hours. However, the values of UV index never exceed the extreme value (i.e. ≥9) at any hour of the day throughout the whole period of study.

Estimation of daily global solar radiation from measured temperatures at Cañada de Luque, Córdoba, Argentina

Solar radiation is the most important source of renewable energy in the planet; it's important to solar engineers, designers and architects, and it's also fundamental for efficiently determining irrigation water needs and potential yield of crops, among others. Complete and accurate solar radiation data at a specific region are indispensable. For locations where measured values are not available, several models have been developed to estimate solar radiation. The objective of this paper was to calibrate, validate and compare five representative models to predict global solar radiation, adjusting the empirical coefficients to increase the local applicability and to develop a linear model. All models were based on easily available meteorological variables, without sunshine hours as input, and were used to estimate the daily solar radiation at Cañada de Luque (Córdoba, Argentina).As validation, measured and estimated solar radiation data were analyzed using several statistic coefficients. The results showed that all the analyzed models were robust and accurate (R2 and RMSE values between 0.87 to 0.89 and 2.05 to 2.14, respectively), so global radiation can be estimated properly with easily available meteorological variables when only temperature data are available.Hargreaves-Samani, Allen and Bristow-Campbell models could be used with typical values to estimate solar radiation while Samani and Almorox models should be applied with calibrated coefficients. Although a new linear model presented the smallest R2 value (R2 = 0.87), it could be considered useful for its easy application. The daily global solar radiation values produced for these models can be used to estimate missing daily values, when only temperature data are available, and in hydrologic or agricultural applications.

Seasonality of vitamin D status in older people in Southern Germany: implications for assessment

from a clinical and public health perspective, it is important to understand the influence of seasonality on the serum vitamin D level to adequately assess and interpret an individual measurement. Therefore, the aim of this study was to analyse the effects of seasonal conditions on 25-hydroxyvitamin D (25(OH)D) serum levels in a population-based cohort of older people. between March 2009 and April 2010 the 25(OH)D serum level was assessed in 1,418 community-dwelling individuals living in Germany aged ≥65 years (56.7% men) with no subscribed vitamin D supplementation. Least-square means of monthly 25(OH)D serum levels with 95% confidence intervals (CI) were estimated, adjusted for gender, age and body mass index. Additionally, the proportion of vitamin deficiency (<20 ng/ml), insufficiency (20-<30 ng/ml) and sufficiency (30 ng/ml or higher) were estimated for each month. Finally, mean values of daily total global solar radiation and daylight were calculated for each month. the minimum 25(OH)D serum level was observed in March with 15.4 ng/ml (SD = 6.56 ng/ml) and the maximum in August with 25.6 ng/ml (SD = 6.59 ng/ml). Compared with daylight and global solar radiation the progression over the year was similar but delayed by ∼2 months. The proportion of vitamin D deficiency, insufficiency and sufficiency were 78.8, 19.2 and 1.9% in March and 16.1, 63.4 and 20.5% in August, respectively. vitamin D insufficiency was very common in this cohort and showed a strong seasonal effect with lowest values in March.

Estimation of the daily global solar radiation; Nepal experience

This work focuses on estimation of global solar radiation and, in particular, it explores the effect of precipitation and temperature on solar radiation profile of Kathmandu (Nepal). An accurate knowledge of solar radiation distribution in each particular geographical location is crucial for the promotion of solar energy technology. The best way of knowing the amount of global solar radiation is to install quality instruments at many locations in the given region. This requires their day to day maintenance, recording and calibration, which is very costly in developing countries like Nepal. Thus, the alternative approach is to correlate meteorological measurements with appropriate models and investigate the key parameters. For the research activities the RadEst program has been used. It includes, for evaluating the daily global solar radiation values at a given latitudes, four models which estimate the atmospheric transmissivity by measurements of daily temperature range and precipitations. The model parameters are fitted in 2years data by iterative procedures. The values obtained by these models are, then, compared with measured radiation data. The paper reports graphical and statistical evaluations suggesting that among the four models, the Modular DCBB is the best model for Kathmandu area. This result is useful for designing solar panels able to maximize the harvesting of solar energy and to reduce the chronic shortage of hydrocarbon fuel that Nepal imports in a significant amount each year.