Estimating the Spatial Distribution of Monthly Mean Global Solar Radiation Over Ghana Using the A˙ ngströmPrescott Model
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Date
November, 2016
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Abstract
Quantifying the amount of Global Solar Radiation (GSR) reaching the surface of
the earth over a specified area is essential for both energy technologies such as solar
heating, solar photovoltaics, solar thermal energy, and solar architecture and climate
impact studies. In this study, the A˙ ngströmPrescott sunshine duration model is used
to estimate monthly mean GSR over Ghana from sunshine duration data measured
at twenty synoptic stations distributed across the country. The measured sunshine
duration datasets for the model was obtained from the Ghana Meteorological Agency
(GMet), distributed over the four agro-ecological zones and spanning a 3-year period
(2000 – 2002). The estimated monthly mean GSR datasets were then gridded at
a spatial resolution of 10 km 10 km, establishing the trend and distribution of
Global Solar Radiation across the country. The gridded dataset was then compared
with satellite data from the National Renewable Energy Laboratory (NREL) and the
German Aerospace Centre (DLR) at a spatial resolution of 10 km 10 km. The
results produced appreciable root mean square error values of 1-5, relative mean
difference values of 0.03-0.22, absolute mean percent error of 3-29, and correlation
coefficient values between 57.8% and 66%. In addition, the estimated total monthly
mean Global Solar Radiation over the country is 412.82 MJm2day1 equivalent
to 4778.02 Wm2. The savanna zone has the maximum estimated monthly mean
GSR, with the highest level estimated at Navrongo (20.76 MJm2day1) equivalent
to 240.28 Wm2, showing only 0:32% increment over the study period. The forest
zone has the minimum estimated monthly mean GSR, with the lowest radiation level
estimated at Oda (17.11 MJm2day1) equivalent to 198.03 Wm2. A maximum
and minimum mean clearness index of 0:59 and 0:48 respectively is estimated. This
means an estimated 53% of Solar radiation at the top of the atmosphere reaches the
study area after attenuation. Meanwhile, the maximum annual time series GSR over
the country is within the second trimester of the year (March-April-May), and the
minimum annual time series GSR are within the wet and harmattan periods of the
year. The satellite data has a total monthly mean Global Solar Radiation of 366.62
MJm2day1 equivalent to 4243.30 Wm2.
The study shows that solar radiation levels over the country (17.11 MJm2day1 to
20.76 MJm2day1), meet the international solar technology market standards of
18.7 MJm2day1 to 20.7 MJm2day1 for the operation of photovoltaic systems
and solar collectors for industrial and domestic applications.
Description
A Thesis Submitted to the Deparment of Physics,
Kwame Nkrumah University of Science and Technology
in partial fulfillment of the requirements for the degree
of Master of Philosophy in Meteorology and Climate Science,