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This article was downloaded by: [Universitaets und Landesbibliothek]On: 19 January 2014, At: 15:52Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK
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Solar Radiation over Doha (Qatar)YOUSEF A. G. ABDALLA aa Mechanical and Chemical Engineering Department , Gulf Polytechnic , P.O. Box 32038, IsaTown, State of BahrainPublished online: 19 Oct 2007.
To cite this article: YOUSEF A. G. ABDALLA (1987) Solar Radiation over Doha (Qatar), International Journal of Solar Energy,5:1, 1-9, DOI: 10.1080/01425918708914406
To link to this article: http://dx.doi.org/10.1080/01425918708914406
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Int. J. Solar Energy, 1987, Vol. 5, pp. 1-9Photocopying permitted by license only© 1987 harwood academic publishers GmbHPrinted in the United Kingdom
Solar Radiation over Doha (Qatar)
YOUSEF A. G. ABDALLA
Mechanical and Chemical Engineering Department, Gulf Polytechnic, P.O. Box32038, Isa Town, State of Bahrain
(Received June 6, 1986)
Measurements of global solar radiation on a horizontal surface and duration ofsunshine are presented. The abundance of solar energy in Doha (Latitude 25°18'N,Longitude 51°33'E) is evident from these data. A correlation between GIGo and thefraction of maximum possible number of bright sunshine hours are determined forDoha and compared with the correlation for Yemen show a good agreement.
The diffuse solar radiation is predicted by two methods which show almost similarresults. Correlation between the diffuse solar radiation as a fraction of the globalDIG and the fraction of maximum possible number of hours of bright sunshine SISois established using the two methods for comparison since direct measurements ofdiffuse solar radiation are not available. The comparison shows a good agreementbetween the two correlations.
KEY WORDS: Solar, radiation, Doha, global.
INTRODUCTION
Knowledge of global solar radiation at any area is important fordesigning solar energy conversion systems. The vital need formeasurement of solar radiation and its analysis for domestic andindustrial applications led to an increased need for detailed information on the distribution of solar energy, specially the global solarradiation.
The paper is a continuation of author's work [1]. The aim of thepresent study is to correlate between global and diffuse solarradiation with number of bright sunshine hours in Doha.
Numerous attempts have been made to supplement such information for various countries. Iqbal [2] has proposed that theaverage horizontal diffuse radiation may be expressed in terms of
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2 Y. A. G. ABDALLA
the fraction of maximum possible sunshine hours. One year later,Iqbal [3] developed empirical equations which correlate the monthlyaverage horizontal diffuse and beam radiation with the fraction ofmaximum possible number of bright sunshine hours. These correlations are based on measured data from the widely spread CanadianStations. Abd El-Salarn [4] investigated the relationships betweenthe diffuse and the total radiation and other more generallyavailable climatological measurements; in order that they may beused for the computation of the diffuse solar radiation componentfor different cities in Egypt where only, any of, the total solarradiation; or the bright sunshine duration; or the amount of cloudcover is known. Gordon and Hochman [5] presented the correlationof beam and global radiation on an hourly, monthly and yearly basisfor Bet Dayan. In a very recent paper, the author and his co-workerBaghdady [6], investigated the relationship between global solarradiation and the number of bright sunshine hours in Bahrain. Thetemporal and spatial fluctuation of the solar radiation incident overthe surface of the earth has necessitated the detailed study of theavailability of solar energy at any specific location and motivatedthe present work.
METHODS OF PREDICTIONS
Solar radiation at normal incidence received at the surface of theearth is subject to variations due to changes in the extraterrestrialradiation. The radiation emitted by the sun looses its intensity inspace only due to the distance traversed. However as the sun's raysenter the earth's atmosphere it continues to suffer additionaldepletions due to absorption and scattering. Hence detailed studiesof solar radiation under local climatic conditions have been carriedout at various places [7-10]. Many attempts have been made topredict the amount of solar radiation at a given location from fewknown parameters [11].
One of the models which is used for prediction of global solarradiation is the Angstrom correlation [12]. The global solar radiation was calculated from the empirical relation given by:
G/Go = A + B(S/So) (1)
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SOLAR RADIATION OVER DOHA (QATAR) 3
(2)
(3)
where G is the monthly average of the daily global radiation on ahorizontal surface, Go is the extraterrestrial solar radiation on themean date of the month, S is the monthly average of daily hours ofbright sunshine, So is the maximum daily hours of sunshine, A andB are regression constants. The study of the latitudinal variation ofthe coefficients in the linear regression equation gave the estimatedvalues of G from known values of S. The values of A and B wereobtained in terms of latitude 1jJ. This is shown in Table I where Aand B have the forms:
A=fIjJ+g
B =pljJ + q
where IjJ is the local latitude. Values of So and Go are computedfrom the following relations [13]:
2So = 15arc cos( -tan IjJ tan fJ)
24 ( 360Ds ) (Go = --;; lo 1 + 0·033 cos 365 cos IjJ cos fJ sin w
2.1t'. ")+360 w sm IjJ sin u
TABLE IValues of f. g. p and q in terms of latitude and month used in the
calculation of the regression coefficientsA and B
Month f g p q
January I -0.00301 0.34507 0.00495 0.34572February I -0.00255 0.33459 0.00457 0.35533March I -0.00303 0.36690 0.00466 0.36377April I -0.00334 0.38557 0.00456 0.35802May I -0.00245 0.35057 0.00485 0.33550June I -0.00327 0.39890 0.00578 0.27292July I -0.00369 0.41234 0.00568 0.27004August I -0.00269 0.36243 0.00412 0.33162September I -0.00338 0.39467 0.00564 0.27125October I -0.00317 0.36213 0.00504 0.31790November I -0.00350 0.36680 0.00623 0.31467December I -0.00350 0.36262 0.00559 0.30676
Year -0.00290 0.36239 0.00491 0.31876Means -0.00313 0.37022 0.00606 0.32029
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4 Y. A. G. ABDALLA
where the solar constant 10 = 1367W1m2, D. is the day number
starting from 1st January, () is the solar declination, w is the hourangle.
The diffuse solar radiation D can be estimated by an empiricalformula which correlates the diffuse component D to the daily totalG. The correlation equation which is widely used is developed byPage [14]:
DIG = 1.00 -1.13 GIGo,
where D is the monthly average of the daily diffuse solar radiationand Go can be obtained from Eq. (3).
Another commonly used correlation is that due to Liu and Jordan[15] and developed by Klein [16] is of the form:
DIG = 1.390 - 4.027G/Go+ 5.53(G/Go)2- 3.108(G/Go)3 (8)
RESULTS AND DISCUSSION
The values of mean monthly hours of sunshine S and the total solarradiation G are given in Table II.
The monthly variation of GIGo, the fraction of possible durationof sunshine hours SISo, and the fraction of diffuse solar radiationDIG are shown in Figure 1. It is seen that these variations are
TABLE IIValues of mean monthly hours of sunshineS and the total solar radiation G (1976
1982).
Month
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
S (hours) G (MJ/m2)
7.7 13.758.0 16.307.8 18.009.0 21.60
10.5 23.4711.4 24.3710.4 22.8110.5 22.5610.1 20.749.7 17.589.0 14.927.5 12.85
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SOLAR RADIATION OVER DOHA (QATAR) 5
0.35
DIG f e q n , (7))
~,/ ~- .._.,; "I "\.,/
o. " LJL-l-l-l-L.-L--.L-L-L--L....:'J FHA H J J A SON D
MONTHS
FIGURE 1 The monthly variations of SISc, GIGo and DIG for Doha.
consistent since the maxima of DIG correspond to the minima ofGIGo and SISo. The highest value of the ratio GIGo is equal to 0.61and it is in June. The maximum value of GIGo stay almost constantfrom the month of May until the month of November except formonth of July. This plateau indicates that Doha possesses sixmonths of good clear days. It is interesting to observe that thecurves of GIGo and SISo drop in the month of July whereas theDIG curve peaks in the same month. This is attributed mainly tothe sand storms that prevail during this month. The GIGo curvedrops to minimum from December through March when clouds and
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6 Y. A. G. ABDALLA
rains are expected. The humidity in these months is high. The peakvalue of SISo occurs in October. Another smaller peak appears inJune. it is, also, shown that the maximum value of SISo is 0.85. Thismaximum value, in addition to the general trend of SISo, is verysimilar to what is found for Bahrain [6]. Figure 1, also, shows theagreement between the values of DIG calculated by eqs. (7) and(8). Both show similar trend. The maximum value of DIG appearsin December.
Regression analysis is carried out between the computed GIGo(using the technique as in [1]) and the 7 years average of SISo. Theresults are shown in Figure 2. The measured GIGo, in addition tothe computed values for Sana'a (Yemen), are also plotted againstthe corresponding values of SISo in the same figure for comparison.The deviation between the computed G and the measured values ofG is always less than 5%. It is found that the measured GIGo satisfies
O.70,-,,----r--,-----r--,-----r----,
• He •• ured (Doha)
COlllputed (Doha)
Computed (S.~.'a)
o. ]0 L-.l-_---'-__...l-_----'__--'--_----'~_...l
0.25 O.lO 0.40 0.50 0.60 0.10 0.80 0.90
5/5 0
FIGURE 2 Values of GIGo vs Corresponding SISo.
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the relation:
SOLAR RADIATION OVER DOHA (QATAR) 7
GIGo =0.383 + 0.267SISo (9)with a correlation coefficient r = 0.904. The sum of the regressionconstants A + B obtained from (9) is 0.650. This sum represents theatmospheric transparency index averaged over the period of 7years. This atmospheric transparency index value shows a goodagreement with that in Figure 1. The deviation between the twovalues is only 6%.
The regression constant A is almost identical to values of A ofShaqra and Al-Hofuf (Saudi Arabia) of similar Latitudes where thevalue B is slightly smaller as shown in reference [17].
Comparing the correlation between GIGo and SISo for Sana'a andDoha, the agreement is good and the slight difference in the valuescan very reasonably be attributed to the difference of environmentalconditions in addition to difference in latitudes.
o."r----~---_._----rr----...,
Die
~ Pale method
.... - .... Liu ,od Jordanmethod
o. 50 0.60 0.10 0.80 0.90
S/So
FIGURE 3 Relationship between DIG and SIs" for Doha.
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8 Y. A. G. ABDALLA
Figure 3 shows the fraction of diffuse solar radiation DIGcomputed by using eqs (7) and (8) vs SISo. The deviation betweenboth correlations is small. The following linear relationship isobtained using equation (7):
DIG = 0.564 - 0.297SISo (10)
with r = -0.905. The second relation is obtained using equation (8):
DIG = 0.492 - 0.242SISo (11)
with r = -0.852.Page correlation depicted higher values than Liu and Jordan
which is in agreement with Fig. 1 and satisfies the results of [1].
CONCLUSIONS
Global solar radiation in Doha has been correlated with duration ofsunshine. This will be helpful for the design of various systemsutilizing solar energy.
The correlation between the fraction of diffuse solar radiation,computed by the two methods, and the fraction of duration ofsunshine is obtained. The agreement between the two methods isvery good. The pattern of fluctuation of DIG is shown to beconsistent with the fluctuation of G IGo and S ISo.
In general, this information contributes to the existing solardistribution data in Qatar and it will be very useful for domestic andindustrial applications in the Gulf area.
References
1. M. K. Baghdady and Yousef, A. G. Abdalla, "Global and Diffuse SolarRadiation in Doba (Qatar}", Internal Report, NO.2, 1984, Gulf Polytechnic,Bahrain.
2. M. Iqbal, "Estimation of the Monthly Average of tbe Diffuse Component ofTotal Insolation of a Horizontal Surface", Solar Energy, Vol. ZO, 1978, P. 101.
3. M. Iqbal, "Correlation of average Diffuse and Beam Radiation with Hours ofBright Sunshine", Solar Energy, Vol. 23, 1979, P. 169.
4. E. M. Abd EI-Salam, "Computation of the Diffuse Solar Radiation for Egypt",International Symposium-workshop on Solar Energy, 16-22 June, 1978.Cairo, Egypt.
5. J. M. Gordon and M. Hochman, "On Correlations Between Beam and GlobalRadiation", Solar Energy, Vol. 32, 1984, P. 329.
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SOLAR RADIATION OVER DOHA (QATAR) 9
6. Yousef, A. G. Abdalla and M. K. Baghdady, "Correlation Between GlobalSolar Radiation with Number of Bright Sunshine Hours in Bahrain", ASME,84-WA/Sol-35,1984.
7. R. K. Swortman, and O. Ogunalade, "Solar Radiation Estimates fromCommon Parameters", Solar Energy, Vol. 12, 1967. P. 170.
8. M. Iqbal, "A study of Canadian diffuse and Total Solar Radiation Data", SolarEnergy, Vol. 12, 1979, P. 81.
9. T. Kusuda and K. Ishii, "Hourly Solar Radiation Data for Vertical andHorizontal Surfaces and Average Days in the United States and Canada", U.S.Department of Commerce National Bureau of Standards. Building ScienceSeries 96, 1976.
10. G. W. Paltridge and D. Proctor, "Monthly Mean Solar Radiation Statisticsfor Australia", Solar Energy, Vol. 18, 1976, P. 235.
II. B. Goldberg, W. H. Klein and R. K. McCartney "A Comparison of SomeSimple Models Used to Predict Solar Irradiance on a Horizontal Surface",Solar Energy, Vol. 23, 1979, P. 81.
12. A. Angstrom, "On the Computation of Global Radiation from Records ofSunshine", Arkiu. Geophsik, Vol. 3,1956, P. 551.
13. J. A. Duffie, and W. A. Beckman, "Solar Energy Thermal Processes", WileyInter Science, New York, 1974.
14. J. K. Page, "Estimation of Monthly Mean Values of Daily Total Short-WaveRadiation on Vertical and Inclined Surfaces from Sunshine Records forLatitudes 4ON-40S", Proc. UN New Sources of Energy, Paper No. 35/5/98,1961, P. S378.
15. B. Y. Liu, and R. D. Jordan, "The Inter-Relationship and CharacteristicDistribution of Direct Diffuse and Total Solar Radiation", Solar Energy, Vol.4, 1960, P. 1.
16. S. A. Klein, "Calculation of Monthly Average Insolation on Tilted Surfaces",Solar Energy, Vol. 9, 1977, P. 325.
17. "Saudi Arabian Solar Radiation Atlas", The Saudi Arabian National Centerfor Science and Technology, Riyadh, 1983.
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