Diffuse solar radiation in Cairo,Egypt

In the present paper, the correlations of Page, Liu and Jordan, and Iqbal were employed to predict the monthly mean daily diffuse solar radiation in Cairo. However, it was found that the coefficients used in these correlations were not applicable in the case of Cairo. New coefficients were obtained and used in the above correlations in order to predict values of the monthly average daily diffuse radiation. The present coefficients were found to be very different from those obtained for conditions in other locations. The estimated diffuse radiations were compared with the measured values. It is concluded that all correlations (i.e. equations which use either the cloudiness index or the relative sunshine) with the present coefficients, may be used to predict the monthly mean daily diffuse radiation in Cairo.     

A study of ultraviolet solar radiation at Cairo urban area, Egypt

The monthly mean values of global, G, and ultraviolet, UV, solar radiation incident on a horizontal surface at Cairo urban area during the two different periods (1969–1973) and (1993–1997) are presented, analyzed and compared. The effect of urbanization processes on the solar radiation components is investigated and discussed. It was found that the total radiation of the two components, G and UV received at the urban area of Cairo during the period (1969–1973) highly exceeds the radiation received during the period (1993–1997) for all months of the year. The mean relative reduction of G and UV reached 17.4% and 27.4% respectively. A significant correlation between G and UV radiation has been established and the recommended correlation equation has been stated to estimate the values of UV radiation that are difficult to measure at any site in the zone of Lower Egypt. Also, a comparative study of the two radiation components, G and UV, at urban (Cairo) and rural (Bahtim) areas during the period (1993–1997) revealed that the urban area always has values of G and UV radiation distinctly lower than that found in rural area for all months of the year. Urban–rural mean reduction of G and UV reached 7.0% and 17.9% respectively. The ratio of the ultraviolet to global radiation (UV/G) are calculated and compared with other sites in the Arabian Peninsula. The effect of atmospheric dust on the measured solar radiation components is also investigated and discussed.     

Estimation and prediction of global solar radiation over Greece

A regression analysis of the relative monthly values of global solar radiation ( ) the corresponding values of sunshine (n/N), for the period 1961-75, was performed to determine the constants a and b of the Ångström formula, for Athens. The constants a and b were also determined by a graphical relationship between the average annual relative sunshine (n/N) and these constants, for the same station. The latter method was then used to determine the constants a and b for 33 other stations widely distributed throughout Greece, after making a relative correction to these constants. In this way, monthly and annual values of global solar radiation were estimated for 34 stations over Greece from sunshine measurements. The geographical distribution of the annual totals of global solar radiation over Greece was mapped and some types and sub-types were identified.Further, a stepwise multiple regression analysis of the annual total amounts of global solar radiation and the three factors (latitude, longitude and altitude) was carried out; the validity of the assumption of the linear relationship between the annual totals of global solar radiation and the three factors was examined.     

Atmospheric turbidity over India from solar radiation measurements

Atmospheric turbidity and pollution have been studied in India for many years. This has been done by means of spectral measurements of direct solar radiation using Ångström pyrheliometers and Volz sun photometers. Radiation attenuation due to dust and haze is a phenomenon of great importance in India during the premonsoon months. Most of the dust content is removed by precipitation during the monsoon, but the haze region is established again as winter sets in over north India.An examination of atmospheric turbidity data over India during the last ten years shows that turbidity has doubled at almost all stations since 1961. This would appear to be associated with increasing pollution caused by rapid industrialization in the various areas under study.     

Mapping global, diffuse and beam solar radiation over Zimbabwe

A database for long-term monthly radiation over Zimbabwe is developed. The meteorological raw data inputs are long-term monthly average records of pyranometer-measured hemispherical radiation, monthly average sunshine records, and satellite-measured hemispherical records over a 2-year period. The sunshine records are incorporated into the database by use of Angstrom-type correlations developed for Zimbabwe, and the short-term satellite data are ‘cultured to long-term ground-measurement basis by means of an empirically derived correlation’ and a ‘time series factor’. Diffuse radiation values are generated from the resulting hemispherical radiation database by a locally developed correlation of the monthly average diffuse fraction of hemispherical radiation with monthly average clearness index. Normal beam radiation is computed from the hemispherical and diffuse radiation using two different methods. The two methods are found to agree generally to within 7%. The results are presented as country-border-contained isolines of radiation. The sensitivity of beam radiation to the accuracy of estimating diffuse radiation is inspected. The sensitivity is quite high, about 1:1 for months and locations with very low clearness. This translates to an almost equal sensitivity of insolation available to tracking tilted apertures, underscoring the importance of developing a local diffuse fraction-clearness index correlation rather than relying on a correlation developed elsewhere.     

Quantifying spatio-temporal dynamics of solar radiation exergy over Turkey

The insensitivity to energy quality is one of the disadvantages of an energy analysis when compared to an exergy analysis. It is only the exergy analysis that clearly reveals the degradation of energy quality in the processes of absorption and emission of solar radiation. The national spatial distribution of mean monthly exergy values of solar radiation over Turkey was mapped at 500-m resolution using universal kriging based on solar radiation data from 152 geo-referenced locations. Mean exergy value of solar radiation in Turkey was estimated at 13.5 ± 1.74MJm^?2day^?1, with a mean annual exergy-to-energy ratio of 0.93.     

Estimation of solar radiation over Jordan—predicted tables

As measured solar radiation data for all parts of Jordan are not available, they have to be estimated using correlation relations and models. This paper presents, for the first time, values of solar radiation over Jordan as estimated from these relations. Measurements of global solar irradiance on a horizontal surface and sunshine duration at nine meteorological stations in Jordan are correlated and used for prediction of the regression coefficients of an Angstrom type correlation relation at these stations and others which only have records of sunshine duration. Regional regression coefficients are obtained and used for prediction of global solar irradiance. The agreement with measurements is better than 5% and 1% on monthly and yearly basis respectively. Estimation of diffuse solar irradiance by Page's and also Liu and Jordan's correlations, as well as the direct beam component are also performed and the results are examined and presented. The abundance of solar energy in Jordan is evident from the daily average global solar irradiance which ranges between 5 and 7 kWh/m². A correlation of Angstrom type of the form: H/Ho = 0.448+0.203 S/So is found suitable for Jordan with correlation coefficient r = 0.93.     

Estimation of solar radiation over Cambodia from long-term satellite data

In this work, monthly average daily global solar irradiation over Cambodia was estimated from a long-term satellite data. A 14-year period (1995–2008) of visible channel data from GMS5, GOES9 and MTSAT-1R satellites were used to provide earth-atmospheric reflectivity. A satellite-based solar radiation model developed for a tropical environment was used to estimate surface solar radiation. The model relates the satellite-derived earth-atmospheric reflectivity to absorption and scattering coefficients of various atmospheric constituents. The absorption of solar radiation due to water vapour was calculated from precipitable water derived from ambient relative humidity and temperature. Ozone data from the TOMS and OMI satellite data were employed to compute the solar radiation absorption by ozone. The depletion of radiation due to aerosols was estimated from the visibility data. Five new solar radiation measuring stations were established at Cambodian cities, namely Siem Reap (13.87°N, 103.85°E), Kompong Thom (12.68°N, 104.88°E), Phnom Penh (11.55°N, 104.83°E), Sihanouke Ville (10.67°N, 103.63°E) and Kampot (10.70°N, 104.28°E). Global solar radiation measured at these stations was used to validate the model. The validation was also carried out by using solar radiation measured at four Thai meteorological stations. These stations are situated near the Cambodian border. Monthly average daily global irradiation from these stations was compared with that calculated from the model. The measured and calculated irradiation is in good agreement, with the root mean square difference of 6.3%, with respect to the mean values. After the validation, the model was used to calculate monthly average daily global solar irradiation over Cambodia. Based on this satellite-derived irradiation, solar radiation maps for Cambodia were generated. These maps show that solar radiation climate of this country is strongly influenced by the monsoons. A solar radiation database was also generated for solar energy applications in Cambodia.     

Correlation of global solar radiation with meteorological parameters over Egypt

Global solar radiation measurements on a horizontal surface (G_m), mean daily maximum temperature (T), mean daily relative humidity (RH), mean daily sea level pressure (MSL), mean daily vapor pressure (V) and hours of bright sunshine (S) are presented, analyzed, arranged in tables and graphs and discussed for five selected locations over Egypt. The locations chosen represent the different weather conditions of Egypt. Matrough and Al Arish are in the north, Cairo in the middle and Kharga and Aswan in the south of Egypt. A correlation between the measurements of global solar radiation and the meteorological parameters were given for the considered locations. The common relationship for all Egypt was also estimated. The correlation and the regression coefficients and the standard errors of estimate are listed in Table 1. The values of correlation coefficients vary from 89% to 99% and the errors of estimation are between 0.01 and 0.04.

Table 1. Geographic location of the selected stations and correlation, regression coefficients and standard errors of estimate for the model ((5), (6), (7), (8) and (9))

Full-size table (<1K)

     

Global solar radiation over Turkey: comparison of predicted and measured data

In this study, various regression analyses were applied to estimate monthly mean solar radiation in Turkey, by using and parameters. Also, equations which represent two periods of the year, winter and summer, were developed by using these parameters. The equations developed by using ratio showed good results for the whole country, but, those which included ratio at different cities showed better results. Even better results were obtained when the equations were applied to the summer and winter. In addition to RMSE and MBE statistics, the t-test method and the harmonic analysis were employed to prove that the results are reliable.     

A comparative study to estimate daily diffuse solar radiation over India

A detailed study of monthly average daily diffuse solar radiation for selected Indian locations have been performed using five years (2001–2005) measured data. The data of four prominent locations (Jodhpur, Calcutta, Bombay and Pune), representing varying weather conditions of the entire country, have been taken for the present study. The correlations between the diffuse fraction (H_d/H) and the sunshine fraction (S/S₀) have been developed using regression analysis method for each selected location as well as for all Indian locations, we call it All India Correlation (AIC). The results obtained from present AIC are well compared with the measured data along with the estimates of Liu and Jordan, Gopinathan and Iqbal for different locations. The comparisons between various data conclude that AIC can be used to estimate diffuse fraction for any location in India. For further validation and to show the accuracy of present correlations, statistical tests of root mean square error (RMSE), mean bias error (MBE) and mean percentage error (MPE) are also performed.     

Some comments on time variation in solar radiation over Baghdad, Iraq

In the present work an attempt was made to study and examine some aspects of radiation climatology which are important in solar energy utilization. The yearly cumulative global radiation for Baghdad is 216 MJ/m² per year, while the annual total of daily diffuse radiation at Baghdad is about 70.82 MJ/m². The mean monthly values of clearness index K_T present a maximum of 65.9% in August and a minimum value of 48.4% in January. The annual mean of daily global radiation and its spectral OG1, RG2 and RG8 at Baghdad is about, 18.03, 13.53, 10.86 and 9.36 MJ/m², respectively. Over the year, the highest UV radiation were received during June and July (243 Wh/m²) and the lowest in December (79 Wh/m²). Furthermore, UV radiation constituted on average 3.25% of global radiation.     

Technical note a multiple linear correlation for diffuse radiation from global solar radiation and sunshine data over Egypt

Measurements of global solar radiation, diffuse radiation and sunshine duration data during the period from 1982 to 1988 at different locations over Egypt were used to establish empirical relationships that would connect the daily monthly average diffuse irradiation with both relative sunshine duration and clearness index separately and in combination. The selected locations were chosen to represent the different weather conditions of North, Middle and South Egypt. Our correlation equations were tested using measured data for the year 1992 at the same locations. The correlation connecting diffuse radiation with both clearness index and percentage possible sunshine is found to be applicable over Egypt.     

Investigation of the impact of atmospheric particles on solar radiation at Nsukka, Nigeria

Using a well-calibrated integrating nephelometer of sensitivity 10⁻⁷/m, we have successfully measured the scattering extinction coefficient of atmospheric fine particles, b_sp at Nsukka, Nigeria, at latitude 6.8°N and longitude 7.35°E and an elevation of 488 m above sea level.

The values of b_sp recorded are 10.0 × 10⁻⁴/m (maximum) and 0.17 × 10⁻⁴/m (minimum). We have also investigated the impact of the scattering extinction coefficient on solar radiation. Results of our investigation reveal that, for high b_sp, mean insolation is generally low, and the reverse is the case for low b_sp. It appears that there is no correlation between instantaneous (hourly) extinction coefficient and insolation for the period covered.     

The distribution of global solar radiation over the land surfaces of the earth

The history, present world distribution and accuracy of measurements of global solar radiation are briefly reviewed. 221 annual total values measured during 1975 with thermopile pyranometers, were used to map the world distribution of solar irradiation and statistically analyze its variation with latitude, altitude and longitude in the northern and southern hemispheres. The pole-to-pole distribution of irradiation was fitted by cubic splines with seven knots giving a standard deviation that was 12 per cent of the average irradiation over the Earth's land surface. The distribution based on the 1975 data is compared with previously published analyses and current uncertainties and gaps in the world measurement network are discussed.     

Global solar radiation estimation

This paper presents the comparison between the observed and estimated values of global solar radiation on horizontal surfaces obtained from the linear Angstrom type of correlation of Rehman and Halawani [1] for 52 cities spread in 11 countries; viz. India, Egypt, Sri Lanka, Spain, Zimbabwe, Yemen, Sudan, Italy, Zambia, Hong Kong, and Malaysia. The comparisons are also made with the local linear models wherever available. The estimated values are compared with the measured values in terms of percent error, mean bias error (MBE), mean absolute bias error (MABE), root mean square error (RMSE), and mean percent error (MPE). This study finds that the model of Rehman and Halawani [1] is capable of giving estimates within an acceptable mean percent error of 5% and less for 33% of cities and between 5–10% for 50% of cities.     

The solar radiation resource

We discuss the characteristics of solar radiation which are most useful for the assessment of solar technologies. Graphs are presented which show the total annual insolation incident on the principal tracking and non-tracking collectors. Additional graphs are developed for the latitudinal and seasonal variations of solar radiation in the absence of an atmosphere. These are then compared with measurements averaged over the U.S. SOLMET sites to provide an understanding of the role of atmospheric effects on the seasonal variations of solar radiation.     

Transient and analytical solution of suspended flat-plate solar air heater

Based on a simple transient analysis, an explicit expression for the temperature of air, flowing through the channel of a suspended flat-plate solar air heater, has been developed as a function of time and space co-ordinates. Investigations regarding the effect of various parameters, such as air velocity, air channel depth and inlet air temperature, on the performance of the system have been carried out under two modes of operation; (1) the time is kept constant while the space co-ordinate along the flow direction is varied, and (2), the latter is kept constant while the former is varied.     

Analysis of solar radiation measurements at Athens Observatory and estimates of solar radiation in Greece

In this paper measurements of Global (G) Solar Radiation on a horizontal surface at Athens during the 16 yr period 1960-75 are analysed. Mean annual, monthly and daily totals, the diurnal variation, frequency distribution of daily totals, frequency of occurrence of daily totals of Global Radiation less than 8.5, 17, and 34 MJ/m² for 2, 3, 4 and 5 successive days are computed and discussed.Direct Solar Radiation at normal incidence (I) is computed and analysed in a similar manner to that of Global Radiation, for the same period. Components of direct radiation of normal incidence have been computed from spot value observations at times when sky conditions permitted.Annual values of global radiation were estimated from sunshine measurements (1960-73) widely distributed throughout Greece. It is considered that this analysis of measurements should closely represent the radiation climatology of Greece.