Estimation of global solar radiation on horizontal surfaces in Jeddah, Saudi Arabia

The measured data of global solar radiation on a horizontal surface, as well as the number of sunshine hours, mean daily ambient temperature, maximum and minimum ambient temperatures, relative humidity and amount of cloud cover, for Jeddah (latitude 21° 42′37″N, longitude 39° 11′12″E), Saudi Arabia for the period 1996–2006 are analyzed. The data are divided into two sets. The sub-data set 1 (1996–2004) are employed to develop empirical correlations between the monthly average of daily global solar radiation fraction (H/H₀) and various meteorological parameters. The nonlinear Angström type model developed by Sen and the trigonometric function model proposed by Bulut and Büyükalaca are also evaluated. New empirical constants for these two models have been obtained for Jeddah. The sub-data set 2 (2005, 2006) are then used to evaluate the derived correlations. Comparisons between measured and calculated values of H have been performed. It is indicated that, the Sen and Bulut and Büyükalaca models satisfactorily describe the horizontal global solar radiation for Jeddah. All the proposed correlations are found to be able to predict the annual average of daily global solar radiation with excellent accuracy. Therefore, the long term performance of solar energy devices can be estimated.     

Measurements and predictions of solar radiation incident on horizontal surfaces at Santa Fe, Argentina (31° 39′S, 60° 43′W)

Measurements and predictions of solar radiation during a period of 10 years on horizontal surfaces at Santa Fe (31° 39′ S, 60° 43′ W), Argentina, reported as average daily global radiation for each month, are presented. Data are compared to those obtained with a previously published and verified model for computing solar radiation on horizontal planes at the earth's surface for cloudless sky days. Measurements show an important reduction of global radiation with respect to the cloudless sky model predictions for all months of the year. Conversely, averaged daily diffuse solar radiation calculated with Page's formula shows a small increment with respect to the predicted diffuse solar radiation for cloudless sky conditions. When direct solar radiation data, calculated from global and diffuse solar radiation values, are compared to theoretical prediction, a significant decrease is observed. This trend is similar to that obtained for global solar radiation.     

Analysis of solar radiation measurements at Al-Arish area, North Sinai, Egypt

This paper presents basic data for a five year period from 1986 to 1990 for global and diffuse solar radiation data at Al-Arish (31°04′N, 33°49′E). These data have been processed, analysed, presented, arranged in tables and graphs and discussed. Mean annual monthly and daily total, the diurnal variation and the frequency of daily totals of global solar radiation are computed and discussed. A correlation between the hourly values of the clearness and diffuse index were obtained and the recommended correlation equations were also given. The isopleths of hourly global radiation were also designed and discussed. The frequency distribution and the frequency of extended periods of low radiation income have been studied which are of particular interest in the field performance of solar energy systems.     

Diffuse fraction of daily global radiation at Dhahran, Saudi Arabia

Relationship between the diffuse fraction of daily global solar radiation and clearness index (the ratio of global to extraterrestrial radiation) is obtained from the radiation data measured at Dhahran (26°32′N, 50°13′E), Saudi Arabia. Two years of daily radiation data calculated from measured one-minute values are used to develop the relationship. Another year of data is used to validate the relationship. Comparison between the present correlation and previous correlations is presented. The present data confirm the seasonal dependence and the location independence of the correlation reported in literature. The diffuse and global solar radiation are presented for dusty and clear days. The results show that the dust significantly increases the diffuse fraction of the global radiation. The diffuse fraction on a typical clear day in March is 0.11, while on a dusty day, in the same month, may be as high as 0.91.     

Estimation of monthly Angström–Prescott equation coefficients from measured daily data in Toledo, Spain

In this study, daily global radiation for Toledo (39°53′05″N, 4°02′58″W, Spain) were utilized to determine monthly-specific equations for estimating global solar radiation from sunshine hours and to obtain improved fits to monthly Angström–Prescott's coefficients.Models were compared using the root mean square error (RMSE), the mean bias error (MBE) and the t-statistic. According to our results, all the models fitted the data adequately and can be used to estimate the specific monthly global solar radiation.Average RMSE and MBE for comparison between observed and estimated global radiation were 1.260 and −0.002 MJ m⁻² day⁻¹, respectively. The t-statistic was used as the best indicator, this indicator depends on both, and is more effective for determining the model performance. The agreement between the estimated and the measured data were remarkable and the method was recommended for use in Toledo (Spain).     

First solar radiation atlas for the Arab world

In the year 1998, the Arab League Educational, Cultural and Scientific Organization (ALESCO), Directorate of Science and Scientific Research, Tunis, had launched the “Solar Radiation Atlas for the Arab World”. This atlas contains three sets of maps (using Mercator projection) for monthly means, where each stands for one month. These are sunshine duration, global solar radiation and diffuse solar radiation. The atlas contains data for nearly 280 stations from 19 Arab states which cover latitudes from 0° (tropic) to 37°N and longitudes 19°E to nearly 60°E with different elevations from the sea level. It also contains useful tables of the monthly recorded means of the direct, diffuse and global solar radiation as well as the sunshine duration for 16 Arab states including 207 cities.The maximum recorded annual mean (10 years) of the global solar radiation in the Arab world was 6.7 kW h/m²/day in Nouakchott (latitude 20°56′N, longitude 17°02′E), Mauritania, and 6.6 kW h/m²/day in Tamenraset (latitude 36°11′N and longitude 5°31′E), Algeria, while the lowest recorded annual mean global solar radiation was 4.1 kW h/m²/day in Mosul (latitude 43°N and longitude 36°E), Iraq. Furthermore, the maximum recorded annual mean sunshine duration in the Arab world was 10.7 h in Aswan (latitude 23°58′N, longitude 32°47′E), Egypt, and the lowest was 7.5 h in Tunis (latitude 36°50′N, longitude 10°14′E), Tunisia.     

Equations for estimating global solar radiation in data sparse regions

The knowledge of the amount of solar radiation in an area/region is very essential in the field of Solar Energy Physics. In this work two equations are put forward for estimating global solar radiation from common climate variables in data sparse regions. The first is the Hargreaves equation, R_s=0.16R_aT_d^0.5 where R_a is the extraterrestrial solar radiation and T_d is the temperature difference (maximum minus minimum), while the second is the Angstrom equation, R_s=R_a(0.28+0.39n/N) where n and N are the measured sunshine hours and the maximum daylight duration respectively. The global solar radiation estimated by the two equations for three sites, Owerri (5°28′N, 7°2′E), Umudike (5°29′N, 7°33′E) and Ilorin (8°32′N, 4°46′E), located in different climate zones of in Nigeria, West Africa, are in agreement with those of earlier workers and that from Photovoltaic Geographic Information System (PVGIS) project. The implication of this in solar photovoltaic applications has been stressed.     

Correlation of global solar radiation values estimated and measured on an inclined surface for clear days in Bogotá

An empirical expression developed to estimate global solar radiation in clear days, on inclined surfaces located at any geographical position, is presented. This expression allows determining the global solar radiation in a specific day of the year, considering the attenuation of radiation in the atmosphere, the air mass factor, astronomic geometric and geographic parameters, and in particular, the altitude.Data calculated with this expression were correlated with those obtained experimentally in Bogotá, Colombia (74°4′W, 4°35′N and 2580 m altitude). The correlation of the calculated with the experimental data yielded a coefficient of 0.9980, which indicates the reliability of the former and that the developed expression facilitates the construction of data bases with information on solar radiation potential in ample regions characterized by their locations at different altitudes above sea level. These data bases will supply preliminary information on sites adequate for the installation of photovoltaic systems.     

Diurnal pattern of global solar radiation in the tropics: a case study in Malaysia

Global solar radiation patterns in Bangi (2°56′7.3″N, 105°47′0.2″E), Malaysia are discussed. The frequency of occurrence of the various solar radiation patterns observed over a 5-year period is derived. These observations will provide useful information for the design of solar energy systems and equipment for installation in tropical countries having a similar global solar radiation pattern.     

An application of the multilayer perceptron: Solar radiation maps in Spain

In this work an application of a methodology to obtain solar radiation maps is presented. This methodology is based on a neural network system [Lippmann, R.P., 1987. An introduction to computing with neural nets. IEEE ASSP Magazine, 4–22] called Multi-Layer Perceptron (MLP) [Haykin, S., 1994. Neural Networks. A Comprehensive Foundation. Macmillan Publishing Company; Hornik, K., Stinchcombe, M., White, H., 1989. Multilayer feedforward networks are universal approximators. Neural Networks, 2(5), 359–366]. To obtain a solar radiation map it is necessary to know the solar radiation of many points spread wide across the zone of the map where it is going to be drawn. For most of the locations all over the world the records of these data (solar radiation in whatever scale, daily or hourly values) are non-existent. Only very few locations have the privilege of having good meteorological stations where records of solar radiation have being registered. But even in those locations with historical records of solar data, the quality of these solar series is not as good as it should be for most purposes. In addition, to draw solar radiation maps the number of points on the maps (real sites) that it is necessary to work with makes this problem difficult to solve. Nevertheless, with the application of the methodology proposed in this paper, this problem has been solved and solar radiation maps have been obtained for a small region of Spain: Jaén province, a southern province of Spain between parallels 38°25′ N and 37°25′ N, and meridians 4°10′ W and 2°10′ W, and for a larger region: Andalucía, the most southern region of Spain situated between parallels 38°40′ N and 36°00′ N, and meridians 7°30′ W and 1°40′ W.     

Global, direct and diffuse solar irradiance in Riyadh, Saudi Arabia

The regression coefficient of the well-known Angstrom correlation are determined for Riyadh city (the capital of Saudi Arabia) longitude 46° 14′E 24°55′N The relationship of the daily and monthly variation of the fraction of the diffuse solar irradiation to extrateresstrial and the clearness index are obtained. The variation of the values of the average daily global solar radiation against the month of the year is reported. The value of K_n defined as the ratio of direct normal Insolation, H_bn measured in Riyadh to direct normal solar extraterrestrial radiation with the K_T and K_d were obtained. The daily diffused ratio and the daily clearness index are shown as a function of the month of the year.     

Parameterization of a simple model to estimate monthly global solar radiation based on meteorological variables, and evaluation of existing solar radiation models for Tabouk, Saudi Arabia

Using 9 years of solar radiation data, we established a simple model to calculate the monthly mean global solar radiation on a horizontal surface in Tabouk (28.38° N, 36.6° E, Saudi Arabia). The model correlates the global solar radiation with five meteorological parameters. These parameters are the perceptible water vapor, air temperature, relative humidity, atmospheric pressure, and the mean monthly daily fraction of possible sunshine hours. The estimated global radiation from the model was compared with the measured values using the mean bias error (MBE), coefficient of correlation (R), root mean square error (RMSE), and mean percentage error (MPE). The t statistics were also applied as another indication of suitability. The model has a high coefficient of correlation (R = 0.99), MBE = −14 × 10⁻⁴ kW h/m², RMSE = 0.10 kW h/m², and MPE = −0.03%. It is believed that the model developed in this work is applicable for estimating, with great accuracy. The monthly mean daily global radiation at any site having similar conditions to those found in Tabouk.Furthermore, 29 regression models available in the literature were used to estimate the global solar radiation data for Tabouk. The selected models were different in terms of the variables they use and in the number of the variables they contained. The models were compared on the basis of the statistical errors considered above. Apart from Abdall’s model, which showed a reasonable estimate (MPE = −2.04%, MBE = −0.22 kW h/m², and RMSE = 0.59 kW h/m²), all the models under or overestimate the measured solar radiation values. Comparisons between these models and the produced model, from this study, were also considered. According to the statistical results, the model of Abdall showed the prediction closest to those estimated using the developed model.     

Comparison of calculated and measured values of total radiation on tilted surfaces in Dhahran, Saudi Arabia

The total radiation data measured at Dhahran (lat. 26°18′N, long. 50°08′E), Saudi Arabia, on a surface inclined at 26° from the horizontal for the period March 1984 to April 1985 was used to test three models for calculation of total radiation on inclined surfaces. These models are one isotropic model and two anisotropic models. The total and diffuse radiation measured on a horizontal surface were used when calculating with these models. The above models were compared on the basis of the statistical error tests using the root mean square error (RMSE) and the mean bias error (MBE). The RMSE varied between 0.399% and 5.578%. Our results were compared with similar calculation for Woodbridge, Ontario, Canada (lat. 43.8°N). The comparison showed that the choice of one or another model is location, inclination of the surface and time dependent. For Woodbridge the anisotropic models Klucher and Hay were found to be more accurate than the isotropic model. The present study shows that, for hot-arid areas, the isotropic model is more accurate for tilt angle values around the latitude of the location.     

Performance evaluation of hybrid (wind/solar/diesel) power systems

Depleting oil and gas reserves, combined with the growing concerns of global warming, have made it inevitable to seek alternative/renewable energy sources. The integration of renewables such as solar and wind energy is becoming increasingly attractive and is being used widely, for substitution of oil-produced energy, and eventually to minimize atmospheric degradation. The literature shows that commercial/residential buildings in Saudi Arabia consume an estimated 10–40% of the total electric energy generated. In the present investigation, hourly wind-speed and solar radiation measurements made at the solar radiation and meteorological monitoring station, Dhahran (26°32′ N, 50°13′ E), Saudi Arabia, have been analyzed to investigate the feasibility of using hybrid (wind+solar+diesel) energy conversion systems at Dhahran to meet the energy needs of twenty 2-bedroom houses. The monthly average wind speeds for Dhahran range from 4.1 to 6.4 m/s. The monthly average daily values of solar radiation for Dhahran range from 3.6 kWh/m² to 7.96 kWh/m². The performance of hybrid systems consisting of different rated power wind farms, photovoltaic (PV) areas, and storage capacities together with a diesel back-up are presented. The monthly average daily energy generated from the above hybrid system configuration has been presented. The deficit energy generated from the back-up diesel generator and the number of operational hours of the diesel system to meet a specific annual electrical energy demand of 702,358 kWh have also been presented.     

Testing of two models for computing global solar radiation on tilted surfaces

Solar radiation data computerly measured at Amman, Jordan was used to verify the performance accuracy of two models for estimation of global radiation on tilted surfaces. The measurements used in this study were the daily totals of global radiation on a horizontal surface, diffuse radiation on a horizontal surface and global radiation on a 45° tilted surface. The measured radiation using microprocessor based weather station was compared with the computerized results obtained from two widely used models for estimating total radiation on tilted surfaces. These are the isotropic model and Hay’s anisotropic model. The study showed that the models are in good agreement with the isotropic model producing slightly better results during the summer months. Hay’s model resulted in better results for the rest of the year.     

Prediction of daily global solar irradiance on horizontal surfaces based on neural-network techniques

In this study, a prediction model of global solar irradiance distribution on horizontal surfaces has been developed. The methodology is based on neural-network techniques and has been applied to the meteorological database of NTUA, Zografou Campus, Athens (37°58′26″N, 23°47′16″E). The investigation of the correlation between weather conditions, duration of daylight and the representative peak value of a Gaussian-type function plays an essential role in the development of the model. The weather conditions are categorized into six different states, whereas the daylight duration is obtained by familiar equations. Thereafter, a correction methodology for the Gaussian-type function—which stands for all six different states—is applied. Finally, the reliability of the developed model is investigated through a suitable validation procedure.     

Relationship between “clearness index” and “cloudiness index” at a tropical station (Ilorin, Nigeria)

Total (global) solar radiation, H, and diffuse solar radiation, H_d were measured at Ilorin (8° 30′N 4° 42′E) Nigeria. From these, the daily values of H/H₀ and H_d/H were computed, where H₀ is the extraterrestrial radiation. The relationship between the two ratios and their variation with the prevailing atmospheric conditions were examined.The ratios were found to be opposite in characteristics. H/H₀ has high values in clear atmospheres and low values in cloudy or turbid atmospheres; and vice-versa for H_d/H. The two ratios are negatively linearly related and with this fact, two simple mathematical models were obtained for estimating H_d/H in terms of H/H₀.     

Prediction of global daily solar radiation using higher order statistics

The main concern of the present paper is to present and to analyse two procedures for modelling daily global solar radiation. The first one uses the clearness index techniques and the second one uses a totally different type of approach for taking in consideration important properties of such data, including non-Gaussian shape and non-stationarity. This procedure uses the difference between the extraterrestrial and the observed daily global radiation denoted “lost solar component”. Both procedures are based on higher order statistics for generating the global solar radiation using mainly a random process. The prediction results show that the sequences of values generated have the same statistical characteristics as those of sequences observed. The comparison between the two methods used indicates that the developed model based on the “lost solar component” is better than the model obtained using the conventional procedure based on the clearness index.     

The contribution of solar gain to space heating

St. George's School, Wallasey, latitude 53°25′N, is heated by solar radiation and heat from the lighting and the occupants; no conventional heating is used. General reasoning suggests that it should be advantageous to use solar heat in this locality in winter. Constructional features associated with the solar design are discussed. The results of an observational study suggest that temperatures of 16°C and above can be achieved in winter; daily mean air temperatures of up to 24.5°C are found in summer, with higher peak values. Serious overheating has occurred but is rare. The heating costs appear to be low compared with some other secondary schools. User study findings are reported. While shortcomings in the Wallasey realisation are noted, it is concluded that the principle of using solar gain to heat buildings is practicable and economic.     

Parametric study of hybrid (wind + solar + diesel) power generating systems

The combined utilization of renewables such as solar and wind energy is becoming increasingly attractive and is being widely used for substitution of oil-produced energy, and eventually to reduce air pollution. In the present investigation, hourly wind-speed and solar radiation measurements made at the solar radiation and meteorological monitoring station, Dhahran (26°32′N, 50°13′E), Saudi Arabia, have been analyzed to study the impact of key parameters such as photovoltaic (PV) array area, number of wind machines, and battery storage capacity on the operation of hybrid (wind + solar + diesel) energy conversion systems, while satisfying a specific annual load of 41,500 kWh. The monthly average wind speeds for Dhahran range from 4.1 to 6.4 m/s. The monthly average daily values of solar radiation for Dhahran range from 3.6 to 7.96 kWh/m². Parametric analysis indicates that with two 10 kW wind machines together with three days of battery storage and photovoltaic deployment of 30 m², the diesel back-up system has to provide about 23% of the load demand. However, with elimination of battery storage, about 48% of the load needs to be provided by diesel system.