- Email: [email protected]
First solar radiation atlas for the Arab world
Renewable Energy 29 (2004) 1085–1107 www.elsevier.com/locate/renene
Data bank
First solar radiation atlas for the Arab world W.E. Alnaser a,, B. Eliagoubi b, A. Al-Kalak b, H. Trabelsi c, M. Al-Maalej d, H.M. El-Sayed e, M. Alloush f a
d
Physics Department, University of Bahrain, College of Science, P.O. Box 32038, Isa Town, Bahrain b Directorate of Science and Scientific Research Programme, Arab League Educational, Cultural and Scientific Organization, Tunis, Bahrain c Trabtech Consult, Tunis, Bahrain Physics Department, University of Tunis, The National Institute for Science & Technology, Tunis, Bahrain e Information Technology Centre, P.O. Box 7664, Damascus, Syria, Bahrain f The National Meteorological Institute, Tunis, Bahrain Received 1 August 2003; accepted 12 October 2003
Abstract 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 v v nearly 280 stations from 19 Arab states which cover latitudes from 0 (tropic) to 37 N and v v 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 v v world was 6.7 kW h/m2/day in Nouakchott (latitude 20 560 N, longitude 17 020 E), Maurv v 2 0 itania, and 6.6 kW h/m /day in Tamenraset (latitude 36 11 N and longitude 5 310 E), Algeria, while the lowest recorded annual mean global solar radiation was 4.1 kW h/m2/day v v in Mosul (latitude 43 N and longitude 36 E), Iraq. Furthermore, the maximum recorded v annual mean sunshine duration in the Arab world was 10.7 h in Aswan (latitude 23 580 N, v v 0 0 longitude 32 47 E), Egypt, and the lowest was 7.5 h in Tunis (latitude 36 50 N, longitude v 10 140 E), Tunisia. # 2004 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +973-782-303; fax: +973-682-582. E-mail address: [email protected] (W.E. Alnaser).
0960-1481/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2003.10.007
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1. Introduction Using solar energy as an alternative source implies two conflicting issues. Firstly, solar energy is a huge, clean, free of charge source of energy. Secondly, the expense of using solar energy is still high and constitutes only a small proportion of the energy used in the world. This means that more research and development is needed as well as making use of other technological advances to lower the cost of solar energy. The efficient use of solar energy requires an accurate knowledge of the solar energy amount available at any one place for certain period. This in turn requires considerable amount of data about the various elements of solar radiation and their spatial and time variations. Different applications of solar energy require measurements and data of different elements of solar radiation. The following elements of solar radiation are the most commonly used in solar energy applications. . The monthly year. . The monthly year. . The monthly year. . The monthly year.
mean of daily sunshine duration and its variation throughout the mean of daily global radiation and its variation throughout the mean of daily diffuse radiation and its variation throughout the mean of daily direct radiation and its variation throughout the
The relevant data for this project have been collected and analyzed by using advanced technical methods in the form of maps and tables for the Eastern Arab states, Western Arab states and for the whole Arab world represented by 18 of its states.
2. Definitions Sunshine duration (S): It is the interval of time during which the solar radiation is intense enough to cast distinct shadows. This element is measured in hours and tenths of an hour by an instrument called heliograph. Direct solar radiation at normal incidence (I): It is the downward solar radiation coming from the solid angle of the sun’s disk. The value of this element varies considerably from one hour to another during the day and from one month to another during the year depending on the latitude and height of the place. It is measured by an instrument called pyrheliometer which is made up of a tube, directed always towards the sun, in such a way that only direct sun rays are allowed to reach the sensitive detection area. Diffuse solar radiation on horizontal surface (D): It is the downward scattered and reflected solar radiation coming from the whole hemisphere of the sky with the exception of the solid angle subtended by the solar disk. This type of radiation has
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a non-zero value even in clear days. It constitutes a small fraction of the global solar radiation during clear days, and forms a large portion of the solar global radiation during cloudy days. It is measured in kW h/m2/day using an instrument called pyranometer which is installed horizontally in such a way that the sensitive detection area is protected by a shading ring from direct sun’s rays. Global solar radiation on a horizontal surface (G): It is the solar radiation, direct and diffuse received from the solid angle of 2p, on a horizontal surface. It is measured in kW h/m2/day using an instrument called pyranometer, which is installed horizontally or inclined without shading the sensitive area. Turbidity: It is an indication of the extinction of the direct solar radiation, regardless of its spectral distribution, by the act of suspended particles such as smoke or dust, which absorbs the solar radiation and diffuses it. 3. Data sources Climatic solar radiation data have been collected from meteorological centers in all but two Arab states for a period of more than 10 years in most cases. This allowed us to derive meaningful statistics of the solar radiation. The atlas contains tabulated data of the solar radiation measuring stations in all Arab states, the longitude and latitude, elements of the measured solar radiation—including the period for which they were measured—such as: sunshine duration (S), global solar radiation on a horizontal surface (G), diffuse solar radiation on a horizontal surface (D), and direct solar radiation at normal incidence (I). 4. Solar radiation measuring instruments The measuring instruments used in most Arab states are as follows: a. Campbell–Stokes heliographs are used for sunshine duration, b. For global solar radiation on a horizontal surface, and for c. Diffuse solar radiation on a horizontal surface, Eppley pyranometer and Kipp and Zonen pyranometer were used except in Libya, where Robitzch pyranometer was used for measuring global radiation. d. For direct solar radiation at normal incidence, Eppley pyrheliometer was commonly used.
5. Data analysis The data were prepared and stored in a computer using EXCEL according to certain rules that enabled easy retrieval. They were also checked, screened and analyzed meticulously to ensure their chronological validity. Validation procedure of observed data: Due to lack of data in some areas, radiation elements such as diffuse and direct solar radiation were estimated using empirical formulas derived from a number of studies conducted in some East and
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West Arab states. The validity of the data was verified by comparing it with that of the neighboring countries. Sunshine duration: The stations that measured this element were so many in that no further work was needed to supplement the network. There are over 250 stations that can measure this element in the Arab world. Periods of observation were reasonably long, reaching 50 years at times. Global solar radiation: In the Eastern Arab states, the number of stations measuring global radiation was 125 stations. They provided us adequate coverage to perform grid point analysis and draw field maps. In the Western Arab states, the number of stations that measures global radiation was about 75. These stations were spread all over the region. Hence, in order to have adequate coverage of all the Western Arab states and their local climates, global radiation was estimated at some locations from sunshine duration by using a locally derived variation of Angstrom type formula: G ¼ Go ðA S=So þ BÞ;
ð1Þ 2
where G is the estimated global solar radiation, in kW h/m /day; Go is the global solar radiation outside the earth’s atmosphere, in kW h/m2/day; S is the sunshine duration in h/day; So is the maximal theoretical daily duration of sunshine calculated in hours; A, B are the constants empirically determined by local studies performed in Morocco and Algeria [1–5]. Diffuse solar radiation: In the Eastern Arab states, the number of stations that measures diffuse radiation was 25 stations and they were distributed as follows: The Kingdom of Saudi Arabia—four stations (Al Kassim, Al Ahsaa, Wadi El Dawasser, Solar village) for 1995, The United Arab Emirates—one station (airport), Kuwait—one station, (Kuwait), The Syrian Arab Republic—three stations, The Arab Republic of Egypt—eight stations, The Hashemite Kingdom of Jordan—eight stations, Bahrain—one station (University of Bahrain). Due to shortage of data, the following general empirical formula was used to calculate the diffused solar radiation from the global solar radiation using similar-type correlation equation to that proposed by Klein [6] and [2], Liu and Jordan [7] i.e. D=G ¼ A þ BK þ CK 2 þ EK 3 ;
ð2Þ
where the mean clearness index (K) is equal to G=Go ; D is the estimated average of diffused solar radiation in kW h/m2/day; G is the daily average of global solar radiation, in kW h/m2/day; Go is the theoretical daily average of global solar radiation outside the earth’s atmosphere in kW h/m2/day [8]. This can be estimated as follows: 24 Isc ½1 þ 0:033cosð360n=365Þ Go ¼ p
½ðcosLÞðcosdÞðcosxÞ þ ð2x=360ÞðsinLÞðsindÞ ; ð3Þ where Isc is solar constant (1353 W/m2), n is the day number starting from 1st January, x is the hour angle, d is the solar declination angle, L is latitude (in degrees).
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The parameters A, B, C, E are constants and were empirically determined from different values of K by using multiple correlation and least square method (LSM) for obtaining the best fitting curve v For the Sudanese station at latitude 10 N, the diffuse solar radiation was calculated from the above formula after using Aswan measurements to determine the constants A, B, C, E as follows [5]: D ¼ Gð 4:33664K 32:5925K 2 þ 15:8257K 3 Þ:
ð4Þ
v
For those Sudanese stations at latitude 10 S, and also for Addis Ababa station (Ethiopia), the diffuse solar radiation was estimated by the following empirical formula which was derived from Bahrain station [9]: D ¼ Gð0:999 1:28KÞ:
ð5Þ
For the Kingdom of Saudi Arabia, based on the city of Riyadh measurements, the empirical formula used to calculate diffuse solar radiation is [9]: D ¼ Gð 16:3814 þ 87:78127K 147:44623K þ 79:9576K 3 Þ:
ð6Þ
The empirical formula for Iraq and Palestine was based on actual measurements in the Jordanian city of Irbid. It took the form [10]: D ¼ Gð1:0278 1:9039K þ 2:362K 2 1:7527K 3 Þ:
ð7Þ
For the state of Qatar, Bahrain, the Sultanate of Oman and United Arab Emirates, the empirical formula for estimating the diffuse solar radiation, based on Abu Dhabi measurements, had the following form [8,10]: D ¼ Gð 1:897 þ 14:536K 26:828K 2 þ 14:976K 3 Þ:
ð8Þ
In the Western Arab states, the number of stations which measured diffuse solar radiation in this region was 11 only and were distributed as follows: Morocco— two stations (Casablanca and Beni Mellal), Algeria—five stations (Oran, Tamanraset, Bichar, Beni Abbes and Algiers), Tunisia—four stations (Tunis, Kairouan, Gafsa and Gabes). No measurements of this element were reported in Libya and Mauritania. Due to scarcity of observations, diffused solar radiation was estimated from global radiation by using the following empirical formula derived experimentally for the city of Casablanca in Morocco [10]: D ¼ Gð 0:759 þ 5:869K 8:8847K 2 þ 3:590K 3 Þ;
ð9Þ
where K ¼ G=Go and D is the estimated average diffused solar radiation in kW h/ m2/day; G is the daily average of global solar radiation, in kW h/m2/day; Go is the theoretical daily average of global solar radiation outside the earth’s atmosphere, in kW h/m2/day. Direct solar radiation: In the Eastern Arab states, data for this element were available from seven stations only and for relatively short periods of time amounting to one year only in one case. Yet direct solar radiation can be estimated from the mean daily values of the global solar radiation and the daily mean of measured
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(or estimated from the global radiation) diffuse solar radiation, but these estimates are not adequately accurate. In the Western Arab states, data for this element were available from four stations only, three of them in Tunisia (Tunis, Kairouan, Gabes), and one in Algeria (Oran). Values were therefore estimated at some selected locations by using the empirical formula [10]: I ¼ kðG DÞ;
ð10Þ
where I is the estimated daily average of direct solar radiation at normal incidence in kW h/m2/day, G is the daily average of global solar radiation, in kW h/m2/ day, D is the daily average of diffused solar radiation, in kW h/m2/day; K is an empirical constant which varies from one month to another. Turbidity: Data for this element were available for four stations only in the Arab Republic of Egypt. Close screening and checking of the available data revealed discrepancies among neighboring stations. In addition, the ad hoc committees in the World Meteorological Organization have recommended a halt on turbidity data collection until better and more accurate methods and measuring techniques are available. Therefore, turbidity data are not included in this atlas. Objective analysis of the data: In order to enrich the data for computer analysis and for preserving the continuity of isolation across countries bordering the Arab states, additional data for the elements of solar radiation were obtained from those countries bordering both Eastern and Western Arab states. In the case of Arab states in the Meghreb area, for instance, data from neighboring countries such as Mali, Niger, Chad, Spain and Italy were used to complete the analysis at border points, and to preserve continuity of isolation across the borders. For the computer analysis itself, well-known ready-made packages such as WINDSURFER and NCAR graphics were used, choosing the most appropriate parameters to fit the climate of the Arab states. Post-verification of the fields generated by the computer was carried out on a number of measuring stations to ensure the adequacy of the used software options. However, there may be some areas where the computerproduced field may not fit the real climatic pattern of a certain radiation element. This is caused mainly by local effects or topography in those areas. 6. Atlas contents The atlas contains three sets of maps. Each set contains 12 maps (using Mercator projection) for monthly means, each indicating one month and one map for the annual mean for each of the following elements: sunshine duration (Figs. 1–3), global solar radiation (Figs. 4–6), diffuse solar radiation (Figs. 7–9). It also contains maps of the measuring stations network in the Arab states for the sunshine duration (Fig. 10), the global solar radiation (Fig. 11), and the diffuse solar radiation (Fig. 12). The atlas also contains tables of monthly averages for the 12 months of the year (at selected Arab stations) for the following radiation elements: daily sunshine duration (Table 1), daily global solar radiation (Table 2), daily diffuse solar radiation (Table 3), and daily direct solar radiation (Table 4).
Fig. 1. The monthly average of the daily sunshine duration in hours for January in Arab countries.
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Fig. 2. The monthly average of the daily sunshine duration in hours for June in Arab countries.
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Fig. 3. The annual average of the monthly sunshine duration in Arab countries.
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Fig. 4. The monthly average of the daily recorded global solar radiation (in kW h/m2/day) for January in Arab countries.
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Fig. 5. The monthly average of the daily recorded global solar radiation (in kW h/m2/day) for June in Arab countries.
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Fig. 6. The annual average of the recorded monthly global solar radiation (in kW h/m2/day) in Arab countries.
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Fig. 7. The monthly average of the daily recorded diffuse solar radiation (in kW h/m2/day) for January in Arab countries.
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Fig. 8. The monthly average of the daily recorded diffuse solar radiation (in kW h/m2/day) for June in Arab countries.
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Fig. 9. The annual average of the recorded monthly diffuse solar radiation (in kW h/m2/day) in Arab countries.
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Fig. 10. Stations’ network of the sunshine duration measurement in the Arab countries.
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Fig. 11. Stations’ network of the global solar radiation measurement in the Arab countries.
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Fig. 12. Stations’ network of the diffuse solar radiation measurement in the Arab countries.
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Table 1 The monthly and annual recorded mean of the sunshine duration (in hours) in most Arab state capitals
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Table 2 The monthly and annual recorded mean of the global solar radiation (in kW h/m2/day) in most Arab state capitals
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Table 3 The monthly and annual recorded mean of the diffuse solar radiation (in kW h/m2/day) in most Arab state capitals
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Table 4 The monthly and annual recorded means of direct solar radiation in kW/m2/day in some Arab state capitals
7. Discussion According to the accurate sunshine duration measurements, taken from 250 stations and spread all over the Arab states, the monthly average sunshine duration v can be as high as 13 h in June for most countries at a latitude of 23–30 N with v least values (10.2 h) in January for Sudan (latitude 12–16 N and a longitude of 23– v 35 E. This figure is very promising for the utilization of solar energy, either for thermal or photovoltaic application. The maximum monthly average global solar radiation on a horizontal surface reaches about 8.3 kW h/m2/day in Jordan’s desert and Saudi Arabia (empty quarter) in June with minimum of 5.0 kW h/m2/ day in countries near the tropic (such as Djibouti and Somalia). In January, the maximum global solar radiation reaches 6.1 kW h/m2/day in the middle of Sudan and reaches minimum (2.5 kW h/m2/day) in countries at the Mediterranean coast. However, the monthly average of diffused solar radiation reaches as high as 1.75 kW h/m2/day in the desert of Saudi Arabia and as low as 1.00 kW h/m2/day in the north of Aljaria for January, while it reaches as high as 3.35 kW h/m2/day in the west coast of Saudi Arabia and east coast of Egypt (Red Sea) and reaches as low as 1.75 kW h/m2/day in Lebanon for the month of June. These values show that, in general, each square meter Arab land receives nearly 640 W. If we assume that the Arab world requires continuous electric power of 100 GW, this could be met easily by installing photovoltaic system with efficiency of 10% covering an area of 1:56 109 m2 (1560 km2), which represents only 0.011% of total area of the Arab world (147 million km2). This atlas will allow researchers to compare their empirical and theoretical equations by estimating the insolations (global, diffused, and direct), from which one can calculate the normal solar radiation. This will allow proper sizing for the applications of solar energy for electrification, cooling air conditioning, transmission, and heating.
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References [1] Bahraoui-Buret J, Bargach MN, Ben Kaddour ML, Leguere JR. Iere etima´tion du gisement solaire marocain a` partir des measures au sol, 1995. [2] Bahraoui-Buret J. Etude du Rayonnement solarire a Rabot A. Khtira revue internationale d’heliotechnique, 1984, p. 207–21. [3] Bahraoui-Buret J, Bargach MN, Ben Kaddour ML. Le gisement solarire Marocain, Centre de promotion des Energies Renouvelables, 1996. [4] Le rayennemet solarire en Algerie. Office National de la Me´te´orologie Oran, 1986. [5] Lebedieva AN. Climatic Atlas of Africa, Part I Gidrometeoizdat, Leningrad, 1978. [6] Klein ASA. Solar Energy 1977;9:327. [7] Liu BT, Jordon RC. Solar Energy 1960;4:1. [8] Alnaser WE. Energy 1989;14(7):409–14. [9] The Saudi Arabian National Center for Science & Technology, Riyadh, Saudi Arabia, Saudi Arabian Solar Radiation Atlas, 1983. [10] Arab League Educational, Cultural and Scientific Organization, Science Department, Tunis, Tunisia, Solar Radiation Atlas for the Arab World, 1977.
Data bank
First solar radiation atlas for the Arab world W.E. Alnaser a,, B. Eliagoubi b, A. Al-Kalak b, H. Trabelsi c, M. Al-Maalej d, H.M. El-Sayed e, M. Alloush f a
d
Physics Department, University of Bahrain, College of Science, P.O. Box 32038, Isa Town, Bahrain b Directorate of Science and Scientific Research Programme, Arab League Educational, Cultural and Scientific Organization, Tunis, Bahrain c Trabtech Consult, Tunis, Bahrain Physics Department, University of Tunis, The National Institute for Science & Technology, Tunis, Bahrain e Information Technology Centre, P.O. Box 7664, Damascus, Syria, Bahrain f The National Meteorological Institute, Tunis, Bahrain Received 1 August 2003; accepted 12 October 2003
Abstract 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 v v nearly 280 stations from 19 Arab states which cover latitudes from 0 (tropic) to 37 N and v v 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 v v world was 6.7 kW h/m2/day in Nouakchott (latitude 20 560 N, longitude 17 020 E), Maurv v 2 0 itania, and 6.6 kW h/m /day in Tamenraset (latitude 36 11 N and longitude 5 310 E), Algeria, while the lowest recorded annual mean global solar radiation was 4.1 kW h/m2/day v v in Mosul (latitude 43 N and longitude 36 E), Iraq. Furthermore, the maximum recorded v annual mean sunshine duration in the Arab world was 10.7 h in Aswan (latitude 23 580 N, v v 0 0 longitude 32 47 E), Egypt, and the lowest was 7.5 h in Tunis (latitude 36 50 N, longitude v 10 140 E), Tunisia. # 2004 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +973-782-303; fax: +973-682-582. E-mail address: [email protected] (W.E. Alnaser).
0960-1481/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2003.10.007
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1. Introduction Using solar energy as an alternative source implies two conflicting issues. Firstly, solar energy is a huge, clean, free of charge source of energy. Secondly, the expense of using solar energy is still high and constitutes only a small proportion of the energy used in the world. This means that more research and development is needed as well as making use of other technological advances to lower the cost of solar energy. The efficient use of solar energy requires an accurate knowledge of the solar energy amount available at any one place for certain period. This in turn requires considerable amount of data about the various elements of solar radiation and their spatial and time variations. Different applications of solar energy require measurements and data of different elements of solar radiation. The following elements of solar radiation are the most commonly used in solar energy applications. . The monthly year. . The monthly year. . The monthly year. . The monthly year.
mean of daily sunshine duration and its variation throughout the mean of daily global radiation and its variation throughout the mean of daily diffuse radiation and its variation throughout the mean of daily direct radiation and its variation throughout the
The relevant data for this project have been collected and analyzed by using advanced technical methods in the form of maps and tables for the Eastern Arab states, Western Arab states and for the whole Arab world represented by 18 of its states.
2. Definitions Sunshine duration (S): It is the interval of time during which the solar radiation is intense enough to cast distinct shadows. This element is measured in hours and tenths of an hour by an instrument called heliograph. Direct solar radiation at normal incidence (I): It is the downward solar radiation coming from the solid angle of the sun’s disk. The value of this element varies considerably from one hour to another during the day and from one month to another during the year depending on the latitude and height of the place. It is measured by an instrument called pyrheliometer which is made up of a tube, directed always towards the sun, in such a way that only direct sun rays are allowed to reach the sensitive detection area. Diffuse solar radiation on horizontal surface (D): It is the downward scattered and reflected solar radiation coming from the whole hemisphere of the sky with the exception of the solid angle subtended by the solar disk. This type of radiation has
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a non-zero value even in clear days. It constitutes a small fraction of the global solar radiation during clear days, and forms a large portion of the solar global radiation during cloudy days. It is measured in kW h/m2/day using an instrument called pyranometer which is installed horizontally in such a way that the sensitive detection area is protected by a shading ring from direct sun’s rays. Global solar radiation on a horizontal surface (G): It is the solar radiation, direct and diffuse received from the solid angle of 2p, on a horizontal surface. It is measured in kW h/m2/day using an instrument called pyranometer, which is installed horizontally or inclined without shading the sensitive area. Turbidity: It is an indication of the extinction of the direct solar radiation, regardless of its spectral distribution, by the act of suspended particles such as smoke or dust, which absorbs the solar radiation and diffuses it. 3. Data sources Climatic solar radiation data have been collected from meteorological centers in all but two Arab states for a period of more than 10 years in most cases. This allowed us to derive meaningful statistics of the solar radiation. The atlas contains tabulated data of the solar radiation measuring stations in all Arab states, the longitude and latitude, elements of the measured solar radiation—including the period for which they were measured—such as: sunshine duration (S), global solar radiation on a horizontal surface (G), diffuse solar radiation on a horizontal surface (D), and direct solar radiation at normal incidence (I). 4. Solar radiation measuring instruments The measuring instruments used in most Arab states are as follows: a. Campbell–Stokes heliographs are used for sunshine duration, b. For global solar radiation on a horizontal surface, and for c. Diffuse solar radiation on a horizontal surface, Eppley pyranometer and Kipp and Zonen pyranometer were used except in Libya, where Robitzch pyranometer was used for measuring global radiation. d. For direct solar radiation at normal incidence, Eppley pyrheliometer was commonly used.
5. Data analysis The data were prepared and stored in a computer using EXCEL according to certain rules that enabled easy retrieval. They were also checked, screened and analyzed meticulously to ensure their chronological validity. Validation procedure of observed data: Due to lack of data in some areas, radiation elements such as diffuse and direct solar radiation were estimated using empirical formulas derived from a number of studies conducted in some East and
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West Arab states. The validity of the data was verified by comparing it with that of the neighboring countries. Sunshine duration: The stations that measured this element were so many in that no further work was needed to supplement the network. There are over 250 stations that can measure this element in the Arab world. Periods of observation were reasonably long, reaching 50 years at times. Global solar radiation: In the Eastern Arab states, the number of stations measuring global radiation was 125 stations. They provided us adequate coverage to perform grid point analysis and draw field maps. In the Western Arab states, the number of stations that measures global radiation was about 75. These stations were spread all over the region. Hence, in order to have adequate coverage of all the Western Arab states and their local climates, global radiation was estimated at some locations from sunshine duration by using a locally derived variation of Angstrom type formula: G ¼ Go ðA S=So þ BÞ;
ð1Þ 2
where G is the estimated global solar radiation, in kW h/m /day; Go is the global solar radiation outside the earth’s atmosphere, in kW h/m2/day; S is the sunshine duration in h/day; So is the maximal theoretical daily duration of sunshine calculated in hours; A, B are the constants empirically determined by local studies performed in Morocco and Algeria [1–5]. Diffuse solar radiation: In the Eastern Arab states, the number of stations that measures diffuse radiation was 25 stations and they were distributed as follows: The Kingdom of Saudi Arabia—four stations (Al Kassim, Al Ahsaa, Wadi El Dawasser, Solar village) for 1995, The United Arab Emirates—one station (airport), Kuwait—one station, (Kuwait), The Syrian Arab Republic—three stations, The Arab Republic of Egypt—eight stations, The Hashemite Kingdom of Jordan—eight stations, Bahrain—one station (University of Bahrain). Due to shortage of data, the following general empirical formula was used to calculate the diffused solar radiation from the global solar radiation using similar-type correlation equation to that proposed by Klein [6] and [2], Liu and Jordan [7] i.e. D=G ¼ A þ BK þ CK 2 þ EK 3 ;
ð2Þ
where the mean clearness index (K) is equal to G=Go ; D is the estimated average of diffused solar radiation in kW h/m2/day; G is the daily average of global solar radiation, in kW h/m2/day; Go is the theoretical daily average of global solar radiation outside the earth’s atmosphere in kW h/m2/day [8]. This can be estimated as follows: 24 Isc ½1 þ 0:033cosð360n=365Þ Go ¼ p
½ðcosLÞðcosdÞðcosxÞ þ ð2x=360ÞðsinLÞðsindÞ ; ð3Þ where Isc is solar constant (1353 W/m2), n is the day number starting from 1st January, x is the hour angle, d is the solar declination angle, L is latitude (in degrees).
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The parameters A, B, C, E are constants and were empirically determined from different values of K by using multiple correlation and least square method (LSM) for obtaining the best fitting curve v For the Sudanese station at latitude 10 N, the diffuse solar radiation was calculated from the above formula after using Aswan measurements to determine the constants A, B, C, E as follows [5]: D ¼ Gð 4:33664K 32:5925K 2 þ 15:8257K 3 Þ:
ð4Þ
v
For those Sudanese stations at latitude 10 S, and also for Addis Ababa station (Ethiopia), the diffuse solar radiation was estimated by the following empirical formula which was derived from Bahrain station [9]: D ¼ Gð0:999 1:28KÞ:
ð5Þ
For the Kingdom of Saudi Arabia, based on the city of Riyadh measurements, the empirical formula used to calculate diffuse solar radiation is [9]: D ¼ Gð 16:3814 þ 87:78127K 147:44623K þ 79:9576K 3 Þ:
ð6Þ
The empirical formula for Iraq and Palestine was based on actual measurements in the Jordanian city of Irbid. It took the form [10]: D ¼ Gð1:0278 1:9039K þ 2:362K 2 1:7527K 3 Þ:
ð7Þ
For the state of Qatar, Bahrain, the Sultanate of Oman and United Arab Emirates, the empirical formula for estimating the diffuse solar radiation, based on Abu Dhabi measurements, had the following form [8,10]: D ¼ Gð 1:897 þ 14:536K 26:828K 2 þ 14:976K 3 Þ:
ð8Þ
In the Western Arab states, the number of stations which measured diffuse solar radiation in this region was 11 only and were distributed as follows: Morocco— two stations (Casablanca and Beni Mellal), Algeria—five stations (Oran, Tamanraset, Bichar, Beni Abbes and Algiers), Tunisia—four stations (Tunis, Kairouan, Gafsa and Gabes). No measurements of this element were reported in Libya and Mauritania. Due to scarcity of observations, diffused solar radiation was estimated from global radiation by using the following empirical formula derived experimentally for the city of Casablanca in Morocco [10]: D ¼ Gð 0:759 þ 5:869K 8:8847K 2 þ 3:590K 3 Þ;
ð9Þ
where K ¼ G=Go and D is the estimated average diffused solar radiation in kW h/ m2/day; G is the daily average of global solar radiation, in kW h/m2/day; Go is the theoretical daily average of global solar radiation outside the earth’s atmosphere, in kW h/m2/day. Direct solar radiation: In the Eastern Arab states, data for this element were available from seven stations only and for relatively short periods of time amounting to one year only in one case. Yet direct solar radiation can be estimated from the mean daily values of the global solar radiation and the daily mean of measured
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(or estimated from the global radiation) diffuse solar radiation, but these estimates are not adequately accurate. In the Western Arab states, data for this element were available from four stations only, three of them in Tunisia (Tunis, Kairouan, Gabes), and one in Algeria (Oran). Values were therefore estimated at some selected locations by using the empirical formula [10]: I ¼ kðG DÞ;
ð10Þ
where I is the estimated daily average of direct solar radiation at normal incidence in kW h/m2/day, G is the daily average of global solar radiation, in kW h/m2/ day, D is the daily average of diffused solar radiation, in kW h/m2/day; K is an empirical constant which varies from one month to another. Turbidity: Data for this element were available for four stations only in the Arab Republic of Egypt. Close screening and checking of the available data revealed discrepancies among neighboring stations. In addition, the ad hoc committees in the World Meteorological Organization have recommended a halt on turbidity data collection until better and more accurate methods and measuring techniques are available. Therefore, turbidity data are not included in this atlas. Objective analysis of the data: In order to enrich the data for computer analysis and for preserving the continuity of isolation across countries bordering the Arab states, additional data for the elements of solar radiation were obtained from those countries bordering both Eastern and Western Arab states. In the case of Arab states in the Meghreb area, for instance, data from neighboring countries such as Mali, Niger, Chad, Spain and Italy were used to complete the analysis at border points, and to preserve continuity of isolation across the borders. For the computer analysis itself, well-known ready-made packages such as WINDSURFER and NCAR graphics were used, choosing the most appropriate parameters to fit the climate of the Arab states. Post-verification of the fields generated by the computer was carried out on a number of measuring stations to ensure the adequacy of the used software options. However, there may be some areas where the computerproduced field may not fit the real climatic pattern of a certain radiation element. This is caused mainly by local effects or topography in those areas. 6. Atlas contents The atlas contains three sets of maps. Each set contains 12 maps (using Mercator projection) for monthly means, each indicating one month and one map for the annual mean for each of the following elements: sunshine duration (Figs. 1–3), global solar radiation (Figs. 4–6), diffuse solar radiation (Figs. 7–9). It also contains maps of the measuring stations network in the Arab states for the sunshine duration (Fig. 10), the global solar radiation (Fig. 11), and the diffuse solar radiation (Fig. 12). The atlas also contains tables of monthly averages for the 12 months of the year (at selected Arab stations) for the following radiation elements: daily sunshine duration (Table 1), daily global solar radiation (Table 2), daily diffuse solar radiation (Table 3), and daily direct solar radiation (Table 4).
Fig. 1. The monthly average of the daily sunshine duration in hours for January in Arab countries.
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Fig. 2. The monthly average of the daily sunshine duration in hours for June in Arab countries.
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Fig. 3. The annual average of the monthly sunshine duration in Arab countries.
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Fig. 4. The monthly average of the daily recorded global solar radiation (in kW h/m2/day) for January in Arab countries.
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Fig. 5. The monthly average of the daily recorded global solar radiation (in kW h/m2/day) for June in Arab countries.
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Fig. 6. The annual average of the recorded monthly global solar radiation (in kW h/m2/day) in Arab countries.
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Fig. 7. The monthly average of the daily recorded diffuse solar radiation (in kW h/m2/day) for January in Arab countries.
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Fig. 8. The monthly average of the daily recorded diffuse solar radiation (in kW h/m2/day) for June in Arab countries.
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Fig. 9. The annual average of the recorded monthly diffuse solar radiation (in kW h/m2/day) in Arab countries.
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Fig. 10. Stations’ network of the sunshine duration measurement in the Arab countries.
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Fig. 11. Stations’ network of the global solar radiation measurement in the Arab countries.
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Fig. 12. Stations’ network of the diffuse solar radiation measurement in the Arab countries.
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Table 1 The monthly and annual recorded mean of the sunshine duration (in hours) in most Arab state capitals
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Table 2 The monthly and annual recorded mean of the global solar radiation (in kW h/m2/day) in most Arab state capitals
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Table 3 The monthly and annual recorded mean of the diffuse solar radiation (in kW h/m2/day) in most Arab state capitals
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Table 4 The monthly and annual recorded means of direct solar radiation in kW/m2/day in some Arab state capitals
7. Discussion According to the accurate sunshine duration measurements, taken from 250 stations and spread all over the Arab states, the monthly average sunshine duration v can be as high as 13 h in June for most countries at a latitude of 23–30 N with v least values (10.2 h) in January for Sudan (latitude 12–16 N and a longitude of 23– v 35 E. This figure is very promising for the utilization of solar energy, either for thermal or photovoltaic application. The maximum monthly average global solar radiation on a horizontal surface reaches about 8.3 kW h/m2/day in Jordan’s desert and Saudi Arabia (empty quarter) in June with minimum of 5.0 kW h/m2/ day in countries near the tropic (such as Djibouti and Somalia). In January, the maximum global solar radiation reaches 6.1 kW h/m2/day in the middle of Sudan and reaches minimum (2.5 kW h/m2/day) in countries at the Mediterranean coast. However, the monthly average of diffused solar radiation reaches as high as 1.75 kW h/m2/day in the desert of Saudi Arabia and as low as 1.00 kW h/m2/day in the north of Aljaria for January, while it reaches as high as 3.35 kW h/m2/day in the west coast of Saudi Arabia and east coast of Egypt (Red Sea) and reaches as low as 1.75 kW h/m2/day in Lebanon for the month of June. These values show that, in general, each square meter Arab land receives nearly 640 W. If we assume that the Arab world requires continuous electric power of 100 GW, this could be met easily by installing photovoltaic system with efficiency of 10% covering an area of 1:56 109 m2 (1560 km2), which represents only 0.011% of total area of the Arab world (147 million km2). This atlas will allow researchers to compare their empirical and theoretical equations by estimating the insolations (global, diffused, and direct), from which one can calculate the normal solar radiation. This will allow proper sizing for the applications of solar energy for electrification, cooling air conditioning, transmission, and heating.
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