Energy in the Arab world

The present paper deals with energy in the Arab world. Data on Arab energy reserves are given. The relation between energy consumption and economic growth, as indicated by the gross national and domestic products, and other economic and social indices in the Arab world are discussed. The oil surplus money in some Arab countries and its present and future impacts on the economies are assessed. Conclusions are stated for the Arab countries after oil exhaustion. A forecast of energy consumption is presented for 21 Arab countries.     

Energy planning in the Arab world

Efficient use of energy is of interest to the energy surplus regions as well as the energy deficit regions. Similarly concern about energy conservation is not confined to the industrially developed regions of the world. This article discusses energy planning from the Arab point of view. A framework for Arab energy modelling is first described. Then the application of a computer model—that of Mesarovic and Pestel—to Arab energy planning needs is discussed and some of the results are presented. Finally current priorities in Arab energy modelling studies are outlined. The Appendix surveys some existing models which address regional and international energy problems.     

Experimental and theoretical investigation of global and diffuse solar radiation in the United Arab Emirates

In the present study, the global, direct and diffuse components of solar radiation as well as temperature, relative humidity and wind speed have been continuously monitored and analysed on an hourly, daily and monthly basis. The monthly average daily total solar radiation varies from 2700 W h/m² in December to 8000 W h/m² in June with an average clearness index of 0.65. Experimental data are compared to the predictions of different theoretical models as functions of declination and hour angles. Correlations are obtained describing the variation of hourly, daily and monthly averages of total and diffuse solar radiation using polynomial expressions. Empirical correlations describing the dependence of the daily average diffuse to total radiation ratio on the clearness index are also obtained. Data for the daily diffuse to total radiation ratio are compared to correlations obtained by other investigators. The comparison shows a reasonable agreement with some scatter due to the seasonal dependence of the correlation. Comparison of calculations with experimental measurements under clear sky conditions show excellent agreement with a maximum error of 8%.     

First performance analysis of a silicon-cell microcontroller-based solar radiation monitoring system

This paper demonstrates the operation of a low-cost silicon pyranometer in combination with a self-designed low-power microcontroller-based data acquisition system for monitoring global horizontal solar radiation. The performance and behaviour of this low-cost silicon-cell microcontroller-based data acquisition system (SIMBADAS) are studied on the basis of experimental instantaneous global horizontal solar radiation data obtained between January and October 1997. This measurement system operates unattended, collecting and storing data at 10 min intervals. Data from the SolData silicon-cell pyranometer (SolData, 1989) are collected via an on-chip A/D converter and stored in non-volatile memory. Only unprocessed data are stored in memory. Quality control and data analysis are done off-line to minimize system cost and complexity. At the end of each data collection period, the acquired data are transmitted to a computer through the RS232 serial port for subsequent analysis. Digital correction of the signal by means of an auto-correction procedure is then done as the data are retrieved by the computer. This paper also presents initial calibration results where the SIMBADAS was compared against the first class reference, the Eppley (PSP) precision spectral pyranometer. Data covering an almost complete range of atmospheric conditions in Harare has been used to develop calibration coefficients for this silicon-based system. Field tests and comparisons with the Eppley pyranometer have shown that the accuracy of the SIMBADAS measurement system is fairly good, typically ±13 W/m² except during partly cloudy days in which readings could be vastly different. This error is acceptable for a lot of applications and comparable to other similar methods developed so far.     

A comparison of methods for estimating hourly diffuse solar radiation from global solar radiation

Four methods of estimating hourly diffuse irradiation from hourly global irradiation are compared, using global and diffuse irradiation data from the Australian Bureau of Meteorology for five widely separated Australian locations. A development of one of these methods with constants derived from the data for each place is found to perform best when judged on a criterion of absolute error, and this performance in maintained when constants averaged over the five locations are used. The derived constants are also given for all other Australian locations for which both global and diffuse data are available, and a method is suggested for deriving suitable values of the constants for places situated between 20° and 45° S for which only global radiation data are available. A previously reported dependence of the proportion of diffuse radiation on latitude is demonstrated.     

Quality control for solar radiation data

Solar radiation values are difficult to predict or to estimate, due to the multitude of factors affecting radiative transfer in the atmosphere. Whether considering a network of stations or several radiation sensors at a single station, proper calibration procedures of both sensors and data acquisition systems are mandatory.This paper presents a method whereby the interrelationships of signals received from different radiometers at a single site are systematically checked as a means of data control. The various measurements discussed include direct solar, global, diffuse solar and net radiation, albedo, measurements on inclined surfaces and in various bandpasses. The data control method is accomplished by examining ratios, combinations, and comparisons of various measured parameters in addition to calculating some of these parameters by the use of empirical formulae.     

Diffuse solar radiation statistics for Italy

In this paper diffuse radiation is correlated with usually measured or more easy computable quantities in order to have a larger number of data available for the various applications of solar energy. Here are used two types of correlation: (a) diffuse radiation as a function of global and extraterrestrial radiation; (b) diffuse radiation as a function of ralative sunshine and extraterrestrial radiation. On the basis of the above correlations, empirical equations have been proposed and their coefficients have been calculated by fitting the experimental data of three Italian stations. The degree of accuracy of the fit has been estimated by a coefficient introduced and called by us “relative standard error of estimate.” In order to compare the proposed formulas, which have different degrees of freedom, it has been used the test of Gauss modified by us. The values of diffuse radiation obtained by the proposed relations agree very well with the experimental data.     

Investigations of solar radiation detectors using a laboratory test facility for solar radiation meteorological instruments

A laboratory test facility for solar radiation detectors has been built and is in operation at the Aerological Station of the Swiss Meteorological Institute (SAP/SMI). This installation is conceived as a universal test bed for solar radiation exposed meteorological instruments, and consists of a commercially available solar simulator, a laser alignment system, a translation mechanism with instrument mounts, and an adjustable projection mirror. The solar simulator produces a well characterized radiation beam which can be filtered to match the terrestrial or outer space solar spectrum with an irradiance of up to one solar constant (1367 Wm⁻²). The instrument mounts and a HeNe laser beam provide a precise and easy alignment of the reference and the test instruments in the radiation beam, allowing for incident angles in the range of 15°–75°. The measurement is based on a comparison of the response of an active cavity absolute radiometer PMO6 with the signal of the test instrument.Detailed investigations of the Haenni Solar 111B type heliometer have revealed important irregularities in the sunshine threshold irradiance angular distribution. Measurements performed with and without the protection glass cover prove the exceedingly high threshold values at large declination angles to be a consequence of enhanced reflections due to the incident angle and inhomogeneities in the glass cover.Very satisfactory results have also been obtained on characterization measurements of pyranometers showing the mean values of the responsivity to be within 0.8% of the calibration values measured at the world radiation center (WRC) at Davos.     

Estimation of hourly solar radiation for India

The ASHRAE constants predict high values of the hourly beam radiation and very low values of the hourly diffuse radiation when used to predict radiation at Indian locations. Hence a procedure has been developed for the estimation of direct, diffuse and global hourly solar radiation on a horizontal surface for any location in India. To calculate hourly solar radiation, an exponential curve, similar to the one used by ASHRAE, was fitted to the measured solar radiation data of six cities from different regions of India. The statistical analysis was carried out for the data computed using ASHRAE constants and the set of constants obtained for India using the measured data of four different Indian cities selected randomly. Three statistical indicators were used to compare the accuracy of the developed procedure. The results show that ASHRAE constants are not suitable to estimate hourly solar radiation in India. Hourly solar radiation estimated by constants obtained for India are fairly comparable with measured data. The mean percentage error with Indian constants for these four Indian cities was found as low as 2.27, −6.29 and −6.09% for hourly beam, diffuse and global radiation, respectively.     

Stochastic approach for daily solar radiation modeling

Mathematical modeling of solar radiation continues to be an important issue in renewable energy applications. In general, existing models are mostly empirical and data dependent. In this paper, a novel approach for solar radiation modeling is proposed and illustrated. The proposed application consists of hidden Markov processes, which are widely used in various signal processing topics including speech modeling with successful results. In the experimental work, mean of hourly measured ambient temperature values are considered as observations of the model, whereas mean of hourly solar radiation values are considered as the hidden events, which constitute the outcomes of the proposed mathematical model. Both solar radiations and temperatures are converted to quantized number of states. Finally, after a training stage that forms the transition probability values of the described states, the hidden Markov model parameters are obtained and tested. The tests are repeated for various numbers of states and observations are presented. Plausible modeling results with distinct properties in terms of accuracy are achieved.     

Solar position algorithm for solar radiation applications

There have been many published articles describing solar position algorithms for solar radiation applications. The best uncertainty achieved in most of these articles is greater than ±0.01° in calculating the solar zenith and azimuth angles. For some, the algorithm is valid for a limited number of years varying from 15 years to a hundred years. This report is a step by step procedure for implementing an algorithm to calculate the solar zenith and azimuth angles in the period from the year −2000 to 6000, with uncertainties of ±0.0003°. The algorithm is described in a book written by Jean Meeus in 1998. This report is written in a step by step format to simplify the complicated steps described in the book, with a focus on the sun instead of the planets and stars in general. It also introduces some changes to accommodate for solar radiation applications. The changes include changing the direction of measuring azimuth angles to be measured from north and eastward instead of being measured from south and eastward, and the direction of measuring the observer’s geographical longitude to be measured as positive eastward from Greenwich meridian instead of negative. This report also includes the calculation of incidence angle for a surface that is tilted to any horizontal and vertical angle, as described by Iqbals in 1983.     

Estimation of monthly solar radiation distribution for solar energy system analysis

The concept of probability density frequency, which is successfully used for analyses of wind speed and outdoor temperature distributions, is now modified and proposed for estimating solar radiation distributions for design and analysis of solar energy systems. In this study, global solar radiation distribution is comprehensively analyzed for photovoltaic (PV) panel and thermal collector systems. In this regard, a case study is conducted with actual global solar irradiation data of the last 15 years recorded by the Turkish State Meteorological Service. It is found that intensity of global solar irradiance greatly affects energy and exergy efficiencies and hence the performance of collectors.     

Estimating atmospheric ozone for solar radiation models

Absorption of incoming solar radiation by atmospheric ozone, while only a small part of total depletion of the solar beam, can contribute up to 20 per cent or more to the absorption taking place. Good methods exist to estimate absorption by ozone, but these methods require values for ozone amounts present in the beam path. An empirical, mathematical model has been developed that shows close agreement with observed annual ozone contents over North America. Only latitude, longitude, and day of the year are needed as inputs to obtain ozone-depth estimates from the model. The model can be adjusted to provide similar accuracy for most of the world. Seasonal variations are also built into the model.     

Utilization of solar radiation for water photolysis

The objections of Melvin against the photolysis of water as a future source of technical hydrogen are not valid. Sufficient hydrogen to cover the energy requirements of very large numbers of people can, with reasonable assumptions, be expected from relatively small areas: in a hot arid country 1000 megawatts from 40 km². H₂ need not be more expensive than crude oil at the present price, per unit fuel value, if membranes, plus auxiliary equipment, etc., can be provided at 32 $/m². It is concluded that the photochemical option for the utilization of solar energy shows great promise in the long run. However, most of the fundamental research still needs to be done.     

Solar constant values for estimating solar radiation

There are many solar constant values given and adopted by researchers, leading to confusion in estimating solar radiation. In this study, some solar constant values collected from literature for estimating solar radiation with the Ångström-Prescott correlation are tested in China using the measured data between 1971 and 2000. According to the ranking method based on the t-statistic, a strategy to select the best solar constant value for estimating the monthly average daily global solar radiation with the Ångström-Prescott correlation is proposed.     

2007年世界太阳能大会申办侧记

6月21日上午,国际太阳能学会理事会在哥得堡举行了会议,讨论决定2007年世界太阳能大会的举办国。此前,6月14日至19日在此召开了2003年世界太阳能大会。 中国太阳能学会委托清华大学教授、清华阳光科技委主任殷志强同志与中国科学院电工研究所所长孔力研究员前往作申办报告,争取2007年世界太阳能大会在中国北京召开。每个申办国有     

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.     

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.     

A method for estimating monthly global solar radiation

In this paper a method is followed for estimating monthly totals of global solar radiation from a combination of calculations of monthly cloudless global solar radiation, surface meteorological observations, and empirical formulae relating sunshine duration to global solar radiation. The percent deviation of calculated from observed values is not negligible, but is much less than errors obtained by using extraterrestrial solar radiation totals. In case of values of monthly global solar radiation which are estimated for other regions, the resulted possible errors should be determined again. Some techniques leading to adaptation of the regression equations for other areas are argued.