This study estimates the total solar radiation potential over Nairobi City. Several theoretical models based on the initial work of Angstrom have been used to estimate the global solar radiations on a horizontal surface for the city, using bright sunshine hours for the period 2004–2014. The models were developed using the 2004–2012 sunshine hours data and validated by comparing with measured values for 2013 and 2014. Dependencies of the models were tested using Mean Bias Error, Root Mean Square Error, the Nash–Sutcliffe Equation and t-statistics. The result of clearness index for Nairobi shows that the sky is clear all year round except during the June-July-August season where KT is less than 0.5. Most models tested in the current studies were able to adequately estimate daily mean monthly global radiation from sunshine duration with Akinoglu and Ecevit model giving the best estimation.

1.
Akinoglu
,
B. G.
and
Ecevit
,
A.
, “
Construction of a quadratic model using modified Angstrom coefficients to estimate global solar radiation
,”
Sol. Energy
45
,
85
92
(
1990
).
2.
Allen
,
R. G.
,
Pereira
,
L. S.
,
Raes
,
D.
, and
Smith
,
M.
,
Crop Evapotranspiration: Guidelines for Computing Crop Requirements
, FAO Irrigation and Drainage Paper 56 (
FAO
,
Rome
,
1998
).
3.
Alnaser
,
W. E.
, “
New model to estimate the solar global irradiation using astronomical and meteorological parameters
,”
Renewable Energy
3
,
175
177
(
1993
).
4.
Ampratwum
,
D. B.
and
Dorvlo
,
A. S. S.
, “
Estimation of solar radiation from the number of sunshine hours
,”
Appl. Energy
63
,
161
167
(
1999
).
5.
Angstrom
,
A.
, “
Solar and terrestrial radiation. Report to the international commission for solar research on actinometric investigations of solar and atmospheric radiation
,”
Q. J. R. Meteorol. Soc.
50
,
121
126
(
1924
).
6.
Bakirci
,
K.
, “
Correlations for estimation of daily global solar radiation with hours of bright sunshine in Turkey
,”
Energy
34
,
485
501
(
2009
).
7.
Camberlin
,
P.
and
Okoola
,
R. E.
, “
The onset and cessation of the ‘long rains’ in eastern Africa and their interannual variability
,”
Theor. Appl. Climatol.
75
,
43
54
(
2003
).
8.
Chen
,
R.
,
Ersi
,
K.
,
Yang
,
J.
,
Lu
,
S.
, and
Zhao
,
W.
, “
Validation of five global radiation models with measured daily data in China
,”
Energy Convers. Manage.
45
,
1759
1769
(
2004
).
9.
Cooper
,
P. I.
, “
The absorption of radiation in solar stills
,”
Sol. Energy
12
,
333
346
(
1969
).
10.
Duffie
,
J. A.
and
Beckman
,
W. A.
,
Solar Engineering of Thermal Processes
(
John Wiley, Academic Press
,
New York
,
1994
), p.
56
.
11.
Ertecin
,
C.
and
Yaldiz
,
O.
, “
Comparison of some existing models for estimating global solar radiation for Antalya (Turkey)
,”
Energy Covers. Manage.
41
,
311
330
(
2000
).
12.
Fletcher
,
A. L.
and
Moot
,
D. J.
, “
Estimating daily solar radiation in New Zealand using air temperatures
,”
N. Z. J. Crop Hortic. Sci.
35
,
147
157
(
2007
).
13.
Frulla
,
L. A.
,
Gagliardini
,
D. A.
,
Grossi
,
G. H.
,
Lopardo
,
R.
, and
Tarpley
,
J. D.
, “
Incident solar radiation on Argentina from geostationary satellite GOES: Comparison with ground measurements
,”
Sol. Energy
41
,
61
69
(
1988
).
14.
Glover
,
J.
and
McGulloch
,
J. S. G.
, “
The empirical relation between solar radiation and hours of sunshine
,”
Q. J. R. Meteorol. Soc.
84
,
172
175
(
1958
).
15.
Hunt
,
L. A.
,
Kuchar
,
L.
, and
Swanton
,
C. J.
, “
Estimation of solar radiation for use in crop modeling
,”
Agric. For. Meteorol.
91
,
293
300
(
1998
).
16.
Iqbal
,
M.
,
An Introduction to Solar Radiation
(
Academic Press
,
New York
,
1983
).
17.
Iziomon
,
M. G.
and
Mayer
,
H.
, “
Assessment of some global solar radiation parameterizations
,”
J. Atmos. Sol.-Terr. Phys.
64
,
1631
1643
(
2002
).
18.
Jacovides
,
C. P.
and
Kontoyiannis
,
H.
, “
Statistical procedures for the evaluation of evapotranspiration computing models
,”
Agric. Water Manage.
27
,
365
371
(
1995
).
19.
Janjai
,
S.
,
Pankaew
,
P.
, and
Laksanaboonsong
,
J.
, “
A model for calculating hourly global solar radiation from satellite data in the tropics
,”
Appl. Energy
86
,
1450
1457
(
2009
).
21.
Koussa
,
M.
,
Malek
,
A.
, and
Haddadi
,
M.
, “
Statistical comparison of monthly mean hourly and daily diffuse and global solar irradiation models and a Simulink program development for various Algerian climates
,”
Energy Convers. Manage.
50
,
1227
1235
(
2009
).
22.
Krishnaiah
,
T.
,
Rao
,
S. S.
,
Madhumurthy
,
K.
, and
Reddy
,
K. S.
, “
Neural network approach for modelling global solar radiation
,”
J. Appl. Sci. Res.
3
,
1105
1111
(
2007
).
23.
Kumar
,
R.
and
Umanand
,
L.
, “
Estimation of global radiation using clearness index model for sizing photovoltaic system
,”
Renewable Energy
30
,
2221
2233
(
2005
).
24.
Li
,
D. H. W.
and
Lam
,
J. C.
, “
An analysis of climatic parameters and sky condition classification
,”
Build. Environ.
36
,
435
445
(
2001
).
25.
Li
,
D. H. W.
,
Lau
,
C. C. S.
, and
Lam
,
J. C.
, “
Overcast sky conditions and luminance distribution in Hong Kong
,”
Build. Environ.
39
,
101
108
(
2004
).
26.
Liu
,
Y. H.
and
Jordan
,
R. C.
, “
The interrelationship and characteristic distribution of direct, diffuse and total solar radiation from metrological data
,”
Sol. Energy
4
,
1
19
(
1960
).
27.
Lopez
,
G.
,
Martinez
,
M.
,
Rubio
,
M. A.
,
Torvar
,
J.
,
Barbero
,
J.
, and
Batlles
,
F. J.
, “
Estimation of hourly diffuse fraction using a neural network based model
,” in
Proceedings of the Asamblea Hispano-Portugusea de Geodisia y Geofisica
, Lagos, Portugal,
2000
, pp.
425
426
.
28.
Marwal
,
V. K.
,
Punia
,
R. C.
,
Sengar
,
N.
,
Mahawar
,
S.
, and
Dashora
,
P.
, “
A comparative study of correlation functions for estimation of monthly mean daily global solar radiation for Jaipur, Rajasthan (India)
,”
Indian J. Sci. Technol.
5
,
2729
2732
(
2012
).
29.
Massaquoi
,
J. G. M.
, “
Global solar radiation in Sierra Leone (West Africa)
,”
Sol. Wind Technol.
5
,
281
283
(
1988
).
30.
Nakamura
,
K.
, “
City temperature of Nairobi
,”
Jpn. Prog. Climatol.
75
,
61
65
(
1966
).
48.
Ndilemeni
,
C. C.
,
Momoh
,
M.
, and
Akande
,
J. O.
, “
Evaluation of Clearness Index of Sokoto Using Estimated Global Solar Radiation
,”
IOSR- JESTFT
5
,
51
54
(
2013
).
31.
Okoola
,
R. E.
, “
Space-time characteristics of the ITCZ over equatorial eastern Africa during anomalous rainfall years
,” Ph.D. thesis, University of Nairobi, Kenya,
1996
.
32.
Olseth
,
A.
and
Skartveit
,
A.
, “
Solar irradiance, sunshine duration and daylight illuminance derived from METEOSAT data for some European sites
,”
Theor. Appl. Climatol.
69
,
239
252
(
2001
).
33.
Ongoma
,
V.
,
Muthama
,
J. N.
, and
Gitau
,
W.
, “
Evaluation of urbanization influences on urban winds of Kenyan Cities
,”
Ethiop. J. Environ. Stud. Manage.
6
,
223
231
(
2013
).
34.
Opijah
,
F. J.
,
Mukabana
,
J. R.
, and
Ng'ang'a
,
J. K.
, “
Rainfall distribution over Nairobi area
,”
J. Kenya Meteorol. Soc.
1
,
3
13
(
2007
).
35.
Page
,
J. K.
, “
The estimation of monthly mean values of daily total short wave radiation on vertical and inclined surface from sunshine records for latitude 40°N–40°S
,” in
Proceedings of UN Conference on New Sources of Energy
,
1961
, Vol. 4, pp.
378
390
.
36.
Prescott
,
J. A.
, “
Evaporation from water surface in relation to solar radiation
,”
Trans. R. Soc. South Aust.
40
,
114
118
(
1940
).
37.
Revfeim
,
K. J. A.
, “
An interpretation of the coefficients of the Angstrom equation
,”
Sol. Energy
31
,
415
416
(
1983
).
38.
Rietveld
,
M. R.
, “
A new method for estimating the regression coefficients in the formula relating solar radiation to sunshine
,”
Agric. Meteorol.
19
,
243
252
(
1978
).
39.
Ruiz-Arias
,
J. A.
,
Cebecauer
,
T.
,
Tovar-Pescador
,
J.
, and
Súri
,
M.
, “
Spatial disaggregation of satellite-derived irradiance using a high-resolution digital elevation model
,”
Sol. Energy
84
,
1644
1657
(
2010
).
40.
Salima
,
G.
and
Chavula
,
M. S.
, “
Determining Angstrom constants for estimating solar radiation in Malawi
,”
Int. J. Geosci.
3
,
391
397
(
2012
).
41.
Samuel
,
T. D. M. A.
, “
Estimation of global radiation for Sri Lanka
,”
Sol. Energy
47
,
333
337
(
1991
).
42.
Senkal
,
O.
, “
Modeling of solar radiation using remote sensing and artificial neural network in Turkey
,”
Energy
35
,
4795
4801
(
2010
).
43.
Sözen
,
A.
,
Arcaklioğlu
,
E.
, and
Özalp
,
M.
, “
Estimation of solar potential in Turkey by artificial neural networks using meteorological and geographical data
,”
Energy Convers. Manage.
45
,
3033
3052
(
2004
).
44.
Stone
,
R. J.
, “
Improved statistical procedure for the evaluation of solar radiation
,”
Sol. Energy
51
,
289
291
(
1993
).
45.
Trabea
,
A. A.
and
Shaltout
,
M. A. M.
, “
Correlation of global solar-radiation with meteorological parameters over Egypt
,”
Renewable Energy
21
,
297
308
(
2000
).
46.
Turton
,
S. M.
, “
The relationship between total irradiation and sunshine in humid tropics
,”
Sol. Energy
38
,
353
354
(
1989
).
47.
Yang
,
W.
,
Seager
,
R.
,
Cane
,
M. A.
, and
Lyon
,
B.
, “
The annual cycle of east African precipitation
,”
J. Climate
28
,
2385
2404
(
2015
).
You do not currently have access to this content.