Values Of Global Solar Radiation Research Articles

Relating geo-meteorological parameters to global solar radiation for Egypt by Iranna-Bapat's estimation models

Estimation of solar radiation is considered as the most important parameter for the design and development of various solar energy systems. But, the availability of the required data is very scarce and often not readily accessible. The foremost objective of the present study was to estimate the monthly average global solar radiation (GSR) at various locations for Egypt, by the generalised Iranna-Bapat’s model. Iranna-Bapat’s model is developed to estimate the value of global solar radiation at any location on earth surface. This model uses the most commonly measurable meteorological parameters such as ambient temperature, humidity, windspeed, moisture for a given location. A total of 11 locations spread across the country are used to validate this model. The computed values from Iranna-Bapat’s model are compared with the measured values. Iranna-Bapat’s model demonstrated acceptable results, and statistically displayed lower RMSE. Therefore this model could be a good estimator for predicting the global solar radiation at other locations for Egypt, where such data is not available.

Estimation of Global Solar Radiation for Four Selected Sites in Nepal Using Sunshine Hours, Temperature and Relative Humidity

Rational and accurate solar energy databases, essential for designing, sizing and performing the solar energy systems in any part of the world, are not easily accessible in different localities of Nepal. In this study, daily global solar radiation, sunshine hours and meteorological data for Biratnagar, Kathmandu, Pokhara and Jumla have been used to derive the regression constants. The linear regression technique has been used to develop a model for Biratnagar, Kathmandu, Pokhara and Jumla. The model has calculated the global solar radiation for these locations. The values of global solar radiation estimated by the model are found to be in close agreement with measured values of respective sites. The estimated values were compared with Angstrom-Prescott model and examined using the root mean square error (RMSE), mean bias error (MBE), mean percentage error (MPE), coefficient of regression (R), coefficient of determinant (R2) and correlation coefficient (CC) statistical techniques. Thus, the resultant correlations and linear regression relations may be then used for the locations of similar meteorological/geographical characteristics and also can be used to estimate the missing data of solar radiation for the respective site.

Latitude Based Model for Tilt Angle Optimization for Solar Collectors in the Mediterranean Region

This paper inspects the different parameters that intervene in the determination of the optimal tilt angle for maximum solar energy collection. It proposes a method for calculating the optimal tilt angle based upon the values of the daily global solar radiation on a horizontal surface. A computer program using the mathematical model to calculate the solar radiation incident on an inclined surface as a function of the tilt angle is implemented. Four years data of daily global solar radiation on a horizontal surface in 35 sites in different countries of the Mediterranean region is used. The program assumes a due south orientation of the collectors and it determines the optimal tilt angle for maximum solar radiation collection for sites in the Mediterranean region. A regression analysis using the results of the computer simulation is conducted to develop a latitude based tilt angle optimization mathematical model for maximum solar radiation collection for the sites. We tested both a linear and a quadratic model (of the form ax2+bx) for representing the relationship between the annual optimal tilt angle and the site's latitude. The quadratic model is better; it provides very high prediction accuracy. 99.87% of the variation in the annual optimal tilt angle is explained by the variability in site's latitude with an average residual angle of only 0.96° for all 35 sites studied. It also gives an average percentage decrease in the annual solar radiation of only 0.016% when compared with actual optimal tilt angles.

Temporal and spatial variations of global solar radiation over the Qinghai–Tibetan Plateau during the past 40 years

Global solar radiation is of great significance to the balance of ground surface radiation, the energy exchange between the Earth’s surface and atmosphere, and the development of weather and climate systems in various regions. In this study, the monthly global radiation recorded at 23 stations over the Qinghai–Tibetan Plateau (QTP) was utilized to estimate global solar radiation (Q) from sunshine duration and to obtain improved fits to the variation coefficients of the monthly Angstrom–Prescott model (APM). The modeling results were evaluated by calculating the statistical errors, including mean bias error, mean absolute error, root mean square error, and mean relative error. We demonstrate that the monthly Q values can be predicted accurately by APM over the QTP. We also assess the variations of Q values at 116 meteorological stations by APM over the QTP during 1961–2000. The analysis shows that the annual mean sunshine duration amounted to more than 3,000 h over the whole plateau, implying promising prospects for economic applications of solar energy. During the past 40 years, the mean global solar radiation has been relatively high in the western QTP, extending northward to the Inner Mongolian Plateau. Although its decadal variations in the QTP and surrounding regions were inconsistent, the anomaly values of global solar radiation were generally positive during the 1960s and 1970s, indicating that the QTP’s global solar radiation has increased during those periods. The anomaly values were negative during the 1980s and 1990s, showing that the plateau’s global solar radiation has decreased during those periods. Global solar radiation over the QTP is negatively proportional to latitude but positively proportional to altitude and relative sunshine duration. Three factors, the sunshine duration, latitude, and altitude, exert great influence on global surface radiation, of which sunshine duration is most significant. A high-variation-coefficient zone of global solar radiation occurred in the western part of the QTP but, on average, the variation coefficient of the plateau’s global solar radiation was only 0.031, suggesting that the variation in global radiation was relatively stable over the whole QTP.

Predicting global solar radiation for South America

Solar energy is one of the most promising renewable energy sources. The availability of the solar energy potential data is very scarce and often not readily accessible. The main objective of this study was to estimate the monthly average global solar radiation at various locations for South America, by the generalized Iranna-Bapat’s model. Iranna-Bapat’s model is developed to estimate the value of global solar radiation at any location on earth surface. This model uses the most commonly measurable meteorological parameters such as ambient temperature, humidity, wind-speed, moisture for a given location. A total of 35 locations spread across the continent are used to validate this model. The computed values from Iranna-Bapat’s model are compared with the measured values. Iranna-Bapat’s model demonstrated acceptable results, and statistically displayed lower values of RMSEs. Therefore this model could be a good estimator for predicting the global solar radiation at other locations for South America, where such data is not available.

A Suitable Model to Estimate Global Solar Radiation in Black Sea Shoreline Countries

The new model for monthly average data is developed to predict monthly average global radiation with acceptable accuracy. The measured monthly average daily global solar radiation and sunshine duration for Istanbul-Samsun-Trabzon (Turkey), Varna (Bulgaria), and Odessa (Ukraine) were used to establish a second order polynomial equation for a suitable correlation model in Black Sea shoreline countries. Estimated data produced by the model were compared with the measured data. A good agreement between the estimated and the measured values of global solar radiation in Black Sea shoreline countries has been found. The new quadratic model seems to be used to estimate monthly average daily global solar radiation for the Black Sea region where the measured data is scarce.

Experimental study of solar flux energy basing on measured sun covering-rate in the gulf of Tunis, Tunisia

Abstract Knowledge of global solar radiation is required in modeling, performance investigation, and planning of solar energy projects. In this work, a new correlation is proposed to estimate the daily cumulated solar flux in the gulf of Tunis. This correlation is an adequate method to predict cumulated solar flux in this region. Furthermore, several models were applied to predict global solar radiation on horizontal planes from sun covering-rate. These models were derived from the original Angstrom linear regression and modified functions. Six kinds of regression have been adopted, namely linear, quadratic, cubic degree, fourth degree, exponential, and logarithmic. The models were tested for the gulf of Tunis (36°43′04″N latitude and 10°25′41″E longitude), using about 29,388 collected data during 2008 basing on 10 min time step. It is found that the sun covering-rate derived estimates basing on the simple linear Angstrom correlation are confined to within 6% of the measured values, giving reliability to the approval of the determined regression coefficients of the long-term desired predictions in the gulf of Tunis. Then, predicted values of global solar radiation on horizontal surfaces by the adopted models were compared to the measured values on the basis of statistical R -squared analysis for yearly and monthly scales. The results show that forecasting global solar radiation by the tested approaches, basing on sun covering-rate, has proved to be sufficiently reliable but the polynomial fourth degree model showed the best estimation of global solar radiation.

Comparison of empirical and artificial neural network models for the correlation of monthly average global solar radiation with sunshine hours in Minna, Niger State, Nigeria

Monthly average daily values of global solar radiation and sunshine hours over a period of five years (1987-1991) using artificial neural network were developed to predict global solar radiation at Minna which lies on latitude 09.37°N, longitude 06.32° and 265.4 m above sea level. The results were used to compare results from other researchers of different models in the same area. The correlation coefficient of our model was found to be 0.997. These values were found to be higher than the correlation coefficient of other models. The values from our model and other models were tested in terms of mean percentage error (MPE), mean bias error (MBE) and root mean square error (RMSE) and our model was found to have low error values when compared with other models. From the results of these studies, it was found out that all the models have predicting capacity, but our model has better results. This is being recommended for the prediction of global solar radiation for Minna and areas that have similar climate with Minna. Key words: Global solar radiation, artificial neural network, prediction, measured values, models.

An experimental investigation of forced convection flat plate solar air heater with storage material

Solar air heater (SAH) is a heating device that uses the heated air in the drying of agriculture products and many engineering applications. The purpose of the present work is to study a forced convection flat plate solar air heater with granite stone storage material bed under the climatic conditions of Egypt-Aswan. Experiments are performed at different air mass flow rates ; varying from 0.016 kg/s to 0.08 kg/s, for five hot summer days of July 2008. Hourly values of global solar radiation and some meteorological data (temperature, pressure, relative humidities, etc.) for measuring days are obtained from the Egyptian Meteorological Authority, Aswan station. Inlet and outlet temperatures of air from a SAH have been recorded. In this work, attempt has been made to present the temperature distribution in non dimensional form that makes it useable for any region and not restricted to local conditions. The variation of solar radiation, air heater efficiency, Nusselt number and temperature distribution along the air heater are discussed. Comparisons between the calculated values of outlet air temperatures, average air temperatures and storage material temperatures and the corresponding measured values showed good agreement. Comparison between current work and those in previous investigations showed fair agreement.

Transpiração e temperatura foliar da cana-de-açúcar sob diferentes valores de potencial matricial

O objetivo deste trabalho foi avaliar a variação diurna da transpiração e da temperatura foliar da cana-de-açúcar, cv. RB867515, sob diferentes potenciais matriciais de água no substrato de cultivo e as condições meteorológicas em ambiente protegido. O efeito do estresse hídrico na transpiração e temperatura foliar foi determinado a partir da suspensão da irrigação, quando foram realizadas três campanhas de medições, iniciadas aos 122; 150 e 185 dias após o plantio (DAP) até que o potencial matricial de água no substrato (Ψ) alcançasse -1.500 kPa, aproximadamente. Sob ausência de estresse hídrico (Ψ>-50 kPa), a transpiração das plantas atingiu o valor máximo entre 10 e 13 h, próximo de 60; 70 e 100 g planta-1 h-1 para 122; 150 e 185 DAP, respectivamente. Sob condições de estresse hídrico severo (Ψ<-1.100 kPa), houve redução na transpiração diária de aproximadamente 73%, comparativamente às medições realizadas sem estresse e sob condições meteorológicas similares. Em condições de ausência de estresse hídrico e de céu nublado, o valor médio da diferença entre a temperatura foliar e a temperatura do ar foi de -2,9 ºC. Em contraste, sob condições de estresse hídrico severo e valores elevados de radiação solar global, a temperatura foliar chegou a ser 6,6 ºC superior à temperatura do ar.

Performance assessment of Hargreaves model in estimating solar radiation in Abuja using minimum climatological data

Lack of incident solar radiation is a significant impediment for most related research applications. Mathematical models have been handy in reducing challenges being posed by inability of having solar radiation instrumental sites at every point on the Earth. Hargreaves-Samani’s model is one of the several empirical methods so far formulated in estimating global solar radiation (GSR) from maximum and minimum temperature data. Most of these models are often been applied in mid-latitudes. The paper attempts to assess the performance of Hargreaves-Samani’s model in the Savanna region using Abuja as the case study. Estimated values of GSR from one month data adapted from Nigeria meteorological Agency (NIMET); using Hargreaves’ model shows 90% index of agreement (IA) with the observed values; which suggests a good model performance that has significant correction of about 29%. Concepts are suggested on improving the model performance in the savannah region. Key words: Global Solar radiation, air temperature, model validation, inversion-layer.

Monthly mean hourly global solar radiation estimation

In this paper, selected empirical models were used to estimate the monthly mean hourly global solar radiation from the daily global radiation at three sites in the east coast of Malaysia. The purpose is to determine the most accurate model to be used for estimating the monthly mean hourly global solar radiation in these sites. The hourly global solar radiation data used for the validation of selected models were obtained from the Malaysian Meteorology Department and University Malaysia Terengganu Renewable Energy Station. In order to indicate the performance of the models, the statistical test methods of the normalized mean bias error, normalized root mean square error, correlation coefficient and t-statistical test were used. The monthly mean hourly global solar radiation values were calculated by using six models and the results were compared with corresponding measured data. All the models fit the data adequately and can be used to estimate the monthly mean hourly global solar radiation. This study finds that the Collares-Pereira and Rabl model performed better than the other models. Therefore the Collares-Pereira and Rabl model is recommended to estimate the monthly mean hourly global radiations for the east coast of Malaysia with humid tropical climate and in elsewhere with similar climatic conditions.

A topographic geostatistical approach for mapping monthly mean values of daily global solar radiation: A case study in southern Spain

Local topography influences total incoming solar radiation at ground surface in mountainous areas, and so it becomes a key factor for the spatial distribution of plants. However, radiometric stations are often clustered only around farmland or populated areas, usually throughout valleys and flat regions. In this work, we use residual kriging methods to account for cloud- and terrain-related effects, especially when availability of measurements in mountains is scarce. Terrain-related effects have been considered through the terrain elevation and a topographic clear-sky solar radiation model that, additionally, also allow us to consider local clouds effects. Mesoscale-level phenomena were considered through the distance to the coast and the geographical longitude, that partially explain the atmospheric circulation in the studied region. The study has been conducted in the region of Andalusia, in southern Spain, using a target grid support of 1km of grid-spacing and based on a 10-year length experimental dataset of 63 stations. Two different residual kriging approaches were evaluated and compared against ordinary kriging estimates. Overall, all kriging methods showed good skills in predicting the spatial regionalization of the monthly averages of daily solar radiation. The use of the distance to the coast and the geographical longitude enhanced the performance of residual kriging methods. Elevation proved to be important during summer months, while clear-sky solar radiation estimates were helpful especially during winter months. Overall, the RMSE value for ordinary kriging at the validation sites was about 3%. The residual kriging methods were able to outperform ordinary kriging around a 5% in winter and up to a 18% in summer, in relative terms.

Daily total global solar radiation modeling from several meteorological data

This paper investigates the modeling of the daily total global solar radiation in Adana city of Turkey using multi-linear regression (MLR), multi-nonlinear regression (MNLR) and feed-forward artificial neural network (ANN) methods. Several daily meteorological data, i.e., measured sunshine duration, air temperature and wind speed and date of the year, i.e., monthly and daily, were used as independent variables to the MLR, MNLR and ANN models. In order to determine the relationship between the total global solar radiation and other meteorological data, and also to obtain the best independent variables, the MLR and MNLR analyses were performed with the “Stepwise” method in the Statistical Packages for the Social Sciences (SPSS) program. Thus, various models consisting of the combination of the independent variables were constructed and the best input structure was investigated. The performances of all models in the training and testing data sets were compared with the measured daily global solar radiation values. The obtained results indicated that the ANN method was better than the other methods in modeling daily total global solar radiation. For the ANN model, mean absolute error (MAE), mean absolute percentage error (MAPE), correlation coefficient (R) and coefficient of determination (R 2) for the training/testing data set were found to be 0.89/1.00 MJ/m2 day, 7.88/9.23%, 0.9824/0.9751, and 0.9651/0.9508, respectively.

Models for obtaining daily global solar radiation with measured air temperature data in Madrid (Spain)

Solar radiation is a primary driver for many physical, chemical and biological processes on the earth’s surface. Complete and accurate solar radiation data at a specific region are quite indispensable to the solar energy related research. For locations where measured values are not available, a number of formulas and models have been developed to estimate solar radiation. This study aimed to calibrate seven existing models and develop one new model for estimating global solar radiation data using temperature measured data for seven stations located in Madrid, Spain. This work concludes that empirical models based on temperature give good results in any location if the parameters are correctly adjusted. A newly developed model that include the difference between maximum and minimum daily air temperature, and the saturation vapour pressures at temperature maximum and minimum, provided estimates with less error than other models. According to the results, the new model showed the best estimation for all stations and therefore is recommended. It is believed that the model developed in this work is applicable for estimating the daily global solar radiation on a horizontal surface at any site in Community of Madrid, Spain. The daily global solar radiation values produced by this approach can be used in the design and estimation of the performance of solar applications.

Optimization of tilt angle for solar panel: Case study for Madinah, Saudi Arabia

This article analyzes the optimal choice of the tilt angle for the solar panel in order to collect the maximum solar irradiation. In this paper, the collector surface is assumed to be facing toward equator. The study is based upon the measured values of daily global and diffuse solar radiation on a horizontal surface. It is shown that the optimal angle of tilt ( β opt ) for each month, allows us to collected the maximum solar energy for Madinah site. Annual optimum tilt angle is found to be approximately equal to latitude of the location. It is found that the loss in the amount of collected energy when using the yearly average fixed angle is around 8% compared with the monthly optimum tilt β opt .

Evapotranspiração de referência com base na radiação solar global estimada pelo método de Bristow-Campbell

A quantidade de água a ser aplicada em sistemas de irrigação é normalmente calculada com base na evapotranspiração de referência (ETo) da região. Vários métodos podem ser empregados para o cálculo de ETo, sendo o de Hargreaves um dos mais adotados. Esse método utiliza valores estimados da radiação solar global (Rs) com base na diferença entre as temperaturas máxima (Tmáx) e mínima (Tmín) do ar. Entretanto, a Rs pode ser calculada por outros métodos, como o de Bristow-Campbell, que também se baseia na diferença entre Tmáx e Tmín. No presente trabalho, foram estimados valores diários da ETo pelo método de Hargreaves, em Jales - SP, com e sem o uso da equação de Bristow-Campbell para cálculo de Rs. Esses valores foram comparados aos obtidos pelo método de Penman-Monteith, que é considerado padrão para a estimativa de ETo. As avaliações consideraram os períodos úmido e seco na região. O uso da equação de Bristow-Campbell melhorou o desempenho do método de Hargreaves, em relação ao de Penman-Monteith, sendo que durante o período seco do ano o desempenho foi superior ao do período úmido.

Monthly ratios of PAR to global solar radiation measured at northern Tibetan Plateau, China

Using narrowband and broadband solar radiation measurements collected at Wudaoliang (WDL) site in northern Tibetan Plateau (NTP) from September 1993 to December 1998, the relationship between monthly photosynthetically active radiation ( Q P ) and global solar radiation ( R S ) values is analyzed. Temporal variability of the ratio ( Q P / R S ) and its further dependence on several meteorological variables are presented. The narrowband ratio exhibited diurnal and seasonal variability with high values during morning and afternoon hours and low values around noon in winter time, whereas during summer period the ratio was decreased from morning to afternoon. The ratio ( Q P / R S ) was correlated positively with several atmospheric parameters such as water vapor pressure and low-level cloud amount; in contrast, the ratio was negatively correlated with clearness index, relative sunshine duration and atmospheric turbidity. It was also found that both the relative sunshine duration and water vapor pressure are the most influential parameters on the estimations of the spectral PAR ratio. Finally, an empirically derived model is proposed for estimating monthly average PAR values over the northern Tibetan Plateau. Verification results further ensured that the proposed model predicts monthly global PAR values accurately.

Fog reduces transpiration in tree species of the Canarian relict heath-laurel cloud forest (Garajonay National Park, Spain)

The ecophysiologic role of fog in the evergreen heath-laurel 'laurisilva' cloud forests of the Canary Islands has not been unequivocally demonstrated, although it is generally assumed that fog water is important for the survival and the distribution of this relict paleoecosystem of the North Atlantic Macaronesian archipelagos. To determine the role of fog in this ecosystem, we combined direct transpiration measurements of heath-laurel tree species, obtained with Granier's heat dissipation probes, with micrometeorological and artificial fog collection measurements carried out in a 43.7-ha watershed located in the Garajonay National Park (La Gomera, Canary Islands, Spain) over a 10-month period. Median ambient temperature spanned from 7 to 15 degrees C under foggy conditions whereas higher values, ranging from 9 to 21 degrees C, were registered during fog-free periods. Additionally, during the periods when fog water was collected, global solar radiation values were linearly related (r2=0.831) to those under fog-free conditions, such that there was a 75+/-1% reduction in median radiation in response to fog. Fog events greatly reduced median diurnal tree transpiration, with rates about 30 times lower than that during fog-free conditions and approximating the nighttime rates in both species studied (the needle-like leaf Erica arborea L. and the broadleaf Myrica faya Ait.). This large decrease in transpiration in response to fog was independent of the time of the day, tree size and species and micrometeorological status, both when expressed on a median basis and in cumulative terms for the entire 10-month measuring period. We conclude that, in contrast to the turbulent deposition of fog water droplets on the heath-laurel species, which may be regarded as a localized hydrological phenomenon that is important for high-altitude wind-exposed E. arborea trees, the cooler, wetter and shaded microenvironment provided by the cloud immersion belt represents a large-scale effect that is crucial for reducing the transpirational water loss of trees that have profligate water use, such as those of the 'laurisilva'.

Preliminary studies on global solar radiation in Mbalmayo, Cameroon

This paper presents preliminary studies on the global solar radiation in a horizontal surface along with the prevailing meteorological conditions measured during the period 1999-2001 in Mbalmayo, Cameroon. Hourly, daily, and mean monthly values of global solar radiation and meteorological data were obtained from the International Institute of Tropical Agriculture automatic weather station of Mbalmayo. The data were processed as daily, hourly, sum of 10-day data for 8.00/12.00/16.00/20.00 hours, decadal hourly, decadal daily, and mean monthly data. The highest measured daily, decadal hourly, decadal daily, and mean monthly data for global solar radiation in Mbalmayo was found to be 29.7, 2.76, 21.8, and 20.1 MJm2, respectively. The highest hourly global solar radiation value up to 182.44 MJm2 was observed between March 21-31, 1999. Apart from the global solar radiation measurements, the main observed meteorological parameters were, soil temperature, temperature, wind speed, precipitation, and relative humidity. The results show that there exist seasonal tendencies in the variation of global solar radiation. The range of variation of these radiations and the distribution puts Mbalmayo has a high potential for solar energy utilization.