A. Ianetz

Analysis of daily clearness index, global and beam radiation for Beer Sheva, Israel: Partition according to day type and statistical analysis

The magnitude of the daily clearness index KT has been utilized to classify a day as either clear, partially cloudy or cloudy. The range of values for defining a day type was based upon a previous analysis of the Beer Sheva radiation database. These criteria were employed to partition the days according to type and the corresponding monthly average daily values for the clearness index, global, normal incidence and horizontal beam radiation were calculated. A statistical analysis was performed on each of the monthly average daily value subsets to help convey the shape of their respective distribution curves. The monthly average frequency of days according to type was also determined. Such an analysis of the solar radiation database for a particular site can be utilized to determine the relative merits of different types of solar energy conversion systems, e.g. concentrating vis-a-vis non-concentrating solar collector systems. The results of this analysis for Beer Sheva indicate that this region is very amenable to the utilization of non-concentrating solar energy conversion systems, since the combined frequency of both clear and partially cloudy days exceeds 80% annually. In addition, the Beer Sheva region is a prime candidate for the use of solar energy conversion systems utilizing concentrating collectors due to its relatively high frequency of clear days and the fact that the monthly average daily values of the clearness index, even for partially cloudy days, are relatively high (KT > 0.50).

Analysis of the solar radiation data for Beer Sheva, Israel, and its environs

Abstract The solar radiation climate of Beer Sheva, Israel, is reported upon in detail. The database utilized in this analysis consisted of global radiation on a horizontal surface, normal incidence beam radiation, and global radiation on a south-facing surface tilted at 40°. Monthly-average hourly and daily values are reported for each of these three types of measured radiations, together with the calculated monthly-average daily values for the components of the global radiation, viz. the horizontal beam and diffuse radiations. The monthly-average hourly and daily clearness index values have also been calculated and analyzed. Monthly-average daily frequency distributions of the clearness index values are reported for each month. The solar radiation climate of Beer Sheva has also been compared to those reported for a number of countries in this region. The annual-average daily global radiation incident on a horizontal surface is 18.91 MJ/m2 and that for normal incidence beam radiation is 21.17 MJ/m2. The annual-average daily fraction of the horizontal global radiation that is beam is 0.72. The annual-average daily value for the clearness index is 0.587 and the average frequency of clear days annually is 58.6%. We conclude, based upon the above analysis, that Beer Sheva and its environs are characterized by relatively high, average-daily irradiation rates, both global and beam, and a relatively high frequency of clear days.

A method for characterization and inter-comparison of sites with regard to solar energy utilization by statistical analysis of their solar radiation data as performed for three sites in the Israel Negev region

A method for the characterization and inter-comparison of sites with regard to their suitability for utilization of solar energy based upon the statistical analysis of their solar radiation intensities is presented. In this method each monthly data set of the daily global, horizontal beam and diffuse radiation intensities was analyzed and the following parameters were determined: monthly average daily radiation intensity, coefficient of variation, skewness and kurtosis. The values of the skewness and kurtosis have been applied, using generally accepted rules, to describe the distribution curves for each of the radiation intensity data sets. In addition, the same type of statistical analysis was applied to the monthly average daily ratios of the horizontal beam to global radiation, diffuse to global and the clearness index for the three sites. In this investigation, this statistical analysis method has been applied to the global and beam radiation measured at three sites located in the southern, Negev region of Israel, viz., Beer Sheva, Sde Boker and Eilat. The southern region of Israel is characterized by relatively high average daily irradiation intensities for both global and normal incidence radiation. They have been characterized with regard to the distribution of their intensity levels and a site inter-comparison has also been performed. An inter-comparison of the results of these analyses for the three sites has been performed on a monthly basis. The results of this analysis are used both to characterize and compare the composition of the solar radiation at the three sites under investigation. The results of this study will be presented in detail.

Correlations between values of daily beam, diffuse and global radiation for Beer Sheva, Israel

Empirical correlations for predicting both beam and diffuse radiation at Beer Sheva, located in the semi-arid southern region of Israel, have been developed. These equations relate either the beam or the diffuse fraction of the global radiation to the clearness index. The available data, composed of normal incidence beam and global radiation measurements, have been analyzed on both a seasonal and a yearly basis. They have been compared to empirical equations previously reported in the literature for six sites in the Middle East region. In the case of Qidron, Israel, and three Greek sites, there was close agreement between the correlations, whereas in the remaining two sites (Gilat, Israel and Fudhaliyah, Iraq) the correlations were quite different. Reasons for the discrepancies in the latter two cases are presented in the text.

An Inter-Comparison of the Radiation Intensities Measured at Three Sites in the Southern Region of Israel by Regression Analysis

Publisher Summary This chapter explores whether the southern region can be described by a singular set of monthly regression equations. A database consisting of global and normal incidence radiation intensities measured at Beer Sheva, a site in the Negev region of Israel, have been utilized to develop a monthly correlations between Kd, the ratio of the daily diffuse on a horizontal surface to the daily extraterrestrial on a horizontal surface as a function of KD, and the ratio of the daily direct beam on a horizontal surface to the daily extraterrestrial on a horizontal surface. An empirical equation in the form of Kd = a[exp(bKD + cKD2)] has been found to give a very good fit to the experimental data.