Journal of Basic and Applied Sciences Vol. 5, No. 2, 73-77, 2009 ISSN: 1814-8085

ESTIMATION OF GLOBAL AND DIFFUSE SOLAR RADIATION

FOR HYDERABAD, SINDH, PAKISTAN

M. Akhlaque Ahmed, Firoz Ahmad

1 and M. Wasim Akhtar

2

Basic and Applied Science, Sir Syed University of Engineering and Technology, Karachi, Pakistan 1Energy and Environment Research Group, Department of Physics, University of Karachi, Karachi, Pakistan

2Usman Institute of Technology, Karachi, Pakistan

ABSTRACT

Solar radiation studies have been carried out to asses the feasibility of solar Energy utilization at Hyderabad, Sindh,

Pakistan(Latitude25° 35′ N). The result obtained shows the variation of Direct and Diffuse component of solar radiation

in summer and winter months. The contribution of diffuse solar radiation is high during the monsoon months (July and

August) whereas sky condition are clear during winter months. From the estimated values it is found that with the

exception of monsoon month, solar energy can be utilized very efficiently throughout the year.

Keywords: Direct and Diffuse radiation, Sky Condition, Clearness Index, Hyderabad Sindh Pakistan.

INTRODUCTION

With the rapid depletion of fossil fuel reserves, it is feared

that the world will soon run out of its energy resources.

This is a matter of concern for the developing countries

whose economy heavily leans on its use of energy. Under

the circumanstances it is highly desirable that alternate

energy resources should be utilized with maximum

conversion efficiency to cope with the ever increasing

energy demand. Among the non-conventional energy

resources, solar energy, wind energy and Biomas has

emerged as most prospective option for the future.

Detailed information about the availability of solar

radiation on horizontal surface is essential for the

optimum design and study of solar energy conversion

system. For a country like Pakistan, the economical and

efficient application of solar energy seems inevitable

because of abundant sunshine available throughout the

year. Solar radiation data are available for most part of the

world, but is not available for many countries which can

not afford the measurement equipment and techniques

involved. Global solar radiation in Pakistan are measured

at five stations namely Karachi, Lahore, Multan, Quetta

and Islamabad, while diffuse solar radiation are not

observed experimentally in any Meteorological station of

the country. Therefore, it is rather important to develop

method to estimate the global and diffuse solar radiation

using climatological parameters. Several empirical

formula have been developed to calculate the global solar

radiation using various parameters. These parameters

includes i) The sunshine hours (Angstrom, A 1924,

Black, T.N et al., 1954,Glove et al., 1958) ii) The relative

humidity and sunshine hours (Gopi Nathan 1988), the

declination angle and the latitude(Liu, H et al., 1960), The

no of rainy days , sunshine hours latitude and

locations(Ready, 1977), sunshine duration, Relative

humidity max. temperature, latitude, altitude and

location(Sabbagh et al. 1977) and the total ppt, water,

turbidity and surface albedo(Hoyt 1978).

Besides this many other workers have reported the

estimation of Global and Diffuse solar radiation

employing various climatological parameters (Abdullah et

al., 1988, Chandal et al., 2005,Ahmad et al., 2004, Udo

2002, Togrul 2002).

In the present work, solar radiation estimation have been

done for the first time for Hyderabad Sindh, to utilize

solar energy for useful purpose. Prior to this work,

estimation of wind energy potential has also been reported

(Ahmad et al., 2004).

The Hyderabad city has an area of 5519 sq.Km. It is

located at latitude (Φ=25.35° N) and longitude 68o16

/.

east. It is the second largest city of Sindh province having

a population of 2.9 million people. About 50 percent of

this population lives in villages.

The city is famous for its “Wind Catch Chimmnies” over

the houses for intercepting wind, since old days. This

work will help the energy strategist and planners to utilize

the wind and solar energy potential to solve the energy

deficit in this city of abundant sunshine and strong wind,

throughout the year.

METHODS OF PREDICTION

Among the above mentioned empirical models, the most

popular is the regression equation of the Angstrom type

[1].

H/H0 = a + b ( n/N) (1)

Where H is the monthly average daily global solar

radiation falling on a horizontal surface at a particular

J. basic appl. sci.

74

location. Ho is the monthly mean daily radiation on a

horizontal surface in the absence of atmosphere. n is the

monthly mean daily number of hour of observed sunshine

hours , N is the monthly mean value of day length at a

particular location. a and b are climatologically

determined regression constant. n/N is often called the

percentage of possible sunshine hour.

Regression coefficient ”a” and “b” have been obtained

from the relationship given as(Tiwari & Sangeeta 1977)

and also confirmed by Frere et al. method[Frere et

al.1980].

a=-0.110+0.235 cos Φ+0.323(n/N)

b=1.449-0.553 cos Φ-0.694 (n/N) (2)

whereas there are many methods to evaluate these

constants (Ulfat et al., 2005).

For equation (1) the value of H0 is determined using

equation (1.8.3) of Duffi and Beckman (Duffie &

Backman 1991).

Ho = 24/ π Isc ( [1+0.033cos (360n/365)][ cosΦ cosδ sinws

+2Π ws /360sinΦ sinδ] (3)

Where Isc is the solar constant, Φ is the latitude, δ is the

solar declination, ws is the sunset hour angles where

δ =23.45 sin{360*248+n/365} (4)

and { cosws= -tanΦ tanδ } (5)

Prediction of Diffuse Solar Rdiation.Hd

The diffuse solar radiation Hd can be estimated by an

empirical formula which correlates the diffuse solar

radiation component Hd to the daily total radiation H. The

correlation equation which is widely used is developed by

Page (Page, Jk 1964).

Hd /H= 1.00-1.13KT (6)

Where Hd is the monthly mean of the daily Diffuse solar

radiation and KT =H/H0 is the clearness index. Another

commonly used correlation is due to Liu and Jordan

(1960) and developed by Klein (Klein SA, 1977) and is of

the form

Hd /H = 1.390-4.027 KT +5.53 ( KT )2 -3.108 ( KT )

3 (7)

RESULTS AND DISCUSSION

The input parameter for the estimation of monthly

average daily global solar radiation at Hyderabad, Sindh,

Pakistan are shown in Table 1. From this it is observed

that sunshine duration is above 70 percent throughout the

year; with the exception of July-August. Employing these

parameters the regression constant “a” and “b” are

evaluated as a=0.323 and b=0.470. Inserting these values

in equation (1) the monthly average daily Global solar

radiation H is estimated (Fig. 1). The value of H, KT, and

Hd for Hyderabad obtained through various correlation are

shown in Table 2. Also shown in this table is the ratio

D/H0 which shows that for Hyderabad the fraction of

diffuse radiation to Extraterrestrial radiation is not more

than 15 percent, with the exception of July-August.

Diffuse Solar Radiation

The diffuse solar radiation for Hyderabad is estimated by

Page and Liu and Jorden method, as no station in Pakistan

measures Diffuse solar radiation. From the estimated

results it is seen that contribution of diffuse solar radiation

is very low throughout the year with the exception of

monsoon months. The Liu and Jordan method predicts

lower values than the Page correlation. In the absence of

measured values of diffuse radiation it is difficult to

establish the superiority of one over the other. The

contribution of diffuse radiation is below 25 percent.

The availability of direct radiation is therefore very

encouraging from utilization point of view. The

transmission of Hd in Extrateresterial radiation is only 16

percent which rises to 20 percent in July-August. From

the observation of clearness index and ratio of diffuse to

global we conclude that presence of clouds is very rare

even in the monsoon months. This is the most favourable

condition for solar energy utilization.

Fig. 1 presents the plot of global solar radiation at

Hyderabad along with the sunshine Hour and the diffuse

solar radiation estimated by Liu and Jorden and Page

method. A dip is seen for the months of August for

n(Sunshine hour) and hence in the value of H, the global

solar radiation.

Fig: 1 Monthly variation of H,n.Hd (Page and LJ method) for

Hyderabad Sindh.

0

5

10

15

20

25

30

Jan

Feb

Mar

chApr

il

May

June

July

Aug

u.

Sep

t.Oct

Nov.

Dec.

Months

H m

jmd

H

n

Hd Page

Hd LJ

Fig. 1. Monthly variation of H,n,Hd (Page and Liu and

Jorden method) for Hyderabad, Sindh, Pakistan.

Ahmed et al.

75

The transmission through the atmosphere KT alongwith

the percent of diffuse radiation in global radiation is

shown in Fig. 2. The dip in the value of KT is in

accordance with the high value of Hd /H for the same

month. The sky is fairly clear during winter months when

solar radiation is in demand for utilization purpose.

Fig:2 Plot of Monthly variation of clearness index KT Hd/H

Page,Hd/H for LJ and Hd/H0 for Hyderabad, Sindh.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Jan

Feb

Marc

h

April

May

Jun

July

Aug.

Sept.

Oct

Nov.

Dec.

Months

Ratios

Kt

Hd/Hpage

Hd/H LJ

D/H

Fig. 2. Plot of Monthly variation of clearness index KT ,

Hd /H, (Page and LJ) and Hd /H0 for Hyderabad Sindh,

Pakistan.

Sky Condition: Hyderabad

The transparency of the atmosphere is indicated by

fraction of Extraterrestrial radiation that reaches the earth

surface as global solar radiation. It is a measure of the

degree of clearness of the sky. Clearness index is given as

KT =H/ H0

Where KT is clearness index, H is the global solar

radiation and H0 is the Extraterrestrial insolation.

From the estimated value of H for Hyderabad, KT is

calculated and it is very encouraging to note that the sky

over Hyderabad is very clear almost throughout the year

with exception of Jul-Aug. where KT <0.50 (i.e 50

percent).

Statistical Distribution Shown below is the statistical distribution of global solar

radiation which indicates that the availability of global

solar radiation at Hyderabad is well above 70 percent

during summer and winter months while it is only 50

percent in months of July-August which is the monsoon

period in this region.

Statistical Data of Global Solar Radiation

Jan-April Above 67 percent

May-Jun Above 60 percent

Jul-Aug (Monsoon) Above 50 percent

Sept-December Above 65 percent

Variation of Direct and Diffuse Solar Radiation:

Monthly Variation

A large variation in the intensities of Direct and Diffuse

radiation due to cloudiness have been indicated as stated

earlier. The result of the variation is plotted in Fig. 3 to

exhibit the trend of percentage variation of direct and

diffuse solar radiation. The maxima of direct radiation for

the month of April and Nov. are quite appreciable. The

percentage of diffuse radiation contributing to global

radiation is low during winter months (bright clear sky)

and does not exceed 40 percent even in the worst sky

condition. This is confirmed with the low values of KT

and high values of Hd /H (Fig. 2). The result obtained for

Hyderabad Sindh is in accordance with the results of the

earlier work done for Karachi, Pakistan (Ahmad

et.al.1981). The presence of direct radiation in April and

Nov. will be very useful for utilizing it for solar

concentrators, solar cookers and solar furnaces etc. The

Angstrom model for determination of Global solar

radiation and Liu and Jorden model for the estimation of

Diffuse solar radiation exhibits the validity of estimation

for the location under study.

Fig:3 Percentage variation of Direct and Diffuse radiation at

Hyderabad, Sindh,Pakistan.

0

10

20

30

40

50

60

70

80

90

Ja

n

Fe

b

Ma

rch

Ap

ril

Ma

y

Ju

ne

Ju

ly

Au

gu

.

Se

pt.

Oct

No

v.

De

c.

Months

Pe

rce

nta

ge

of

rad

iatio

n.

Direct

Diffuse

Fig. 3. Percentage variation of Direct and Diffuse

radiation at Hyderabad, Sindh, Pakistan.

CONCLUSION

The work reported in this paper indicates that the solar

energy utilization has bright prospects in Hyderabad.

Sindh, Pakistan. The estimated values of global and

J. basic appl. sci.

76

diffuse radiation reveals that solar radiation can be very

efficiently used to compensate for the energy deficit. For

the estimation of diffuse radiation Page and Liu and

Jordan methods are in very good agreement whereas

Angstrom equation calculates the monthly average daily

global solar radiation. Since no research regarding the

potential of solar energy has been done prior to this work,

this work will be very helpful to use these resources at

Hyderabad Sindh. Since the experimental data of Global

and diffuse solar radiation is not available for Hyderabad,

Sindh, the estimation has to be done employing sunshine

hours of the location. Linear and quadratics regression

could be developed, if the measured data for the location

under study is available. However the present work

employing Angstrom-model and Page and Liue and

Jorden model for Global and diffuse solar radiation for

Hyderabad Sindh, serves the purpose very effectively.

The wind energy potential is also encouraging as stated

earlier. Therefore a combination of solar and wind energy

availability will be very helpful in future to use this

tremendous amount of sunshine and high wind energy

potential.

REFERENCES

Abdullah, YAG. and Farugh, GM. 1988. Contribution to

the study of solar radiation in Abu Dhabi. Energy Conv.

and Management. 28(1): 63-67.

Ahmad, Firoz, Hussain, SA., Naqvi, SMMR. and Akhtar,

M. Wasim. 1981.Characteristic Distribution of Total,

Direct and Diffuse solar radiation at Karachi, Pak. Jour.

Sci & Res. 24(5-6): 171.

Ahmad, Firoz and Ulfat Intikhab. 2004. Emperical model

for the correlation of Monthly Average Daily Global

Solar Radiation with hours of sunshine on a horizontal

surface at Karachi, Pakistan. Turkish J. Physics. 28: 301-

307.

Ahmed, Akhlaque M. and Ahmad, Firoz. 2004. Wind

Energy potential and its characteristics distribution for

Table 1. Input Parameters for Estimation of Monthly Average Global Solar Radiation at Hyderabad, Sindh, Pakistan

Months n

(Monthly mean sunshine Hour)

N

(Monthly Average Day length)

n/N(Percentage of

possible sunshine hour)

Jan 7.7 10.62 o.725

Feb 8.7 11.16 0.779

Mar 8.89 11.85 0.750

Apr 9.95 12.61 0.789

May 9.06 13.24 0.684

June 8.41 13.54 0.621

July 7.07 13.41 0.527

Aug 4.77 9.17 0.520

Sep 7.72 12.14 0.636

Oct 8.69 11.40 0.763

Nov 8.89 10.76 0.826

Dec 7.96 10.46 0.761

Table 2. Solar Radiation Data for Hyderabad, Sindh, Pakistan

Months Hest

MJm2d

Ho

MJm2d

- KT=H/H0

Hd / H

Page

Hd / H

LJ

Hd

Page

MJm2d

Hd

LJ

MJm2d

-

Hd /H0

Jan 15.73 23.70 0.663 0.250 0.243 3.93 3.82 0.163

Feb 19.24 27.93 0.688 0.222 0.225 4.27 4.33 0.153

Mar 22.17 32.83 0.675 0.237 0.234 5.25 5.18 0.159

Apr 25.68 37.01 0.693 0.216 0.222 5.54 5.70 0.151

May 25.34 39.32 0.644 0.272 0.256 6.89 6.48 0.169

June 24.62 40.04 0.604 0.307 0.246 7.66 6.05 0.169

July 22.56 39.53 0.570 0.355 0.318 8.00 7.17 0.191

Aug 18.75 37.70 0.497 0.438 0.377 8.21 7.00 0.201

Sep 21.24 34.16 0.621 0.298 0.277 6.33 5.88 0.178

Oct 19.96 29.28 0.681 0.230 0.228 4.59 4.55 0.156

Nov 17.93 24.63 0.727 0.192 0.196 3.38 3.45 0.127

Dec 15.30 22.49 0.680 0.231 0.238 3.53 3.64 0.159

Ahmed et al.

77

power generation at Hyderabad Sindh, Pakistan. Kar.

Univ. Jour. Sci. 32(1 &2): 21-26.

Angstrom, A. 1924. Solar and terrestrial radiation Q.J.R.

Met. Soc. 50: 121-126.

Black, JN., Bonython, CW. and Prescett, JA. 1954. Solar

radiation and duration of Sunshine, Q.J.R Metero. Soc.

80: 231-235.

Chandal, SS., Agarwal, RK., Pandey, AN. 2005. New

correlation to estimate Global Solar Radiation on

Horizontal Surface using sunshine Hours and

Temperature data for Indian Cities. Jour. of Solar Energy

Engineering. 127: 417-420.

Duffie, JA. and Beckman, WA., 1991. Solar Engineering

of Thermal Processes. John-Wiley & Sons, New York.

Frere et al. 1980. Graphs given in A.A Flocas paper

Estimation and prediction of Global Solar Radiation over

Greece. Solar Energy. 24: 63-70.

Glover, J. and McCulloch, F. 1958. The empirical

relationship between solar radiation and hours of

sunshine. Q.J.R. Met. Soc. 84(359): 56-60.

Gopinathan, KK. 1988. A new model for estimating total

solar radiation. Solar and Wind technology. 5(1): 107-

109.

Hoyt, DV., 1978. A model for the calculation of solar

global insolation. Solar Energy. 21: 27-35

Klien, SA. 1977. Calculation of monthly average

insolation on tilted surface. Solar Energy. 9: 325.

Liu, YH. and Jordan, RC. 1960. The inter relationship and

characteristic distribution of direct, diffuse and total solar

radiation from metrological data. Solar Energy. 4: 1-19.

Page, JK. 1964. The estimation of monthly mean values

of daily short wave radiation on vertical and inclined

surface from sunshine records of latitude 40 degree N to

40 degree S. Proc. of UN-Conf. on New Sources of

Energy. l:4 paper s/98. 378

Reddy, SJ. 1971. An empirical method for the estimation

of net radiation intensity Solar Energy. 13: 291-292.

Sabbagh, JA., Sayigh, AAM. and El-Salam, EMA. 1977.

Estimation of the total solar radiation from meteorological

data. Solar Energy.19: 307-311.

Tiwari, GN. and Suleja, Sangeeta. 1997. Solar Thermal

Engineering System, Narosa Publishing House, New

Dehli, India.

Togral, IT. and Hasan, Togrul. 2002. Global solar

radiation over Turkey. Comparison of predicted and

measured data. Renewable Energy. 25: 55

Udo, SO. 2002. Contribution to the relationship between

Solar Radiation and sunshine duration in the tropics: A

study case of experimental data at Illorin, Nigeria.

Turkish J. Physics. 26: 229.

Ulfat, Intikhab, Ahmad, Firoz, Siddiqui, Imran. 2005.

Determination of Angstrom coefficient for the prediction

of monthly average daily Gobal Solar Radiation

Horizontal surface at Karachi, Pakistan. Kar. Univ. Jour.

Sci. 33(1 & 2): 7-11.