Estimating the Spatial Distribution of Monthly Mean Global Solar Radiation Over Ghana Using the A˙ ngström􀀀Prescott Model

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November, 2016
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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˙ ngström􀀀Prescott 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 MJm􀀀2day􀀀1 equivalent to 4778.02 Wm􀀀2. The savanna zone has the maximum estimated monthly mean GSR, with the highest level estimated at Navrongo (20.76 MJm􀀀2day􀀀1) equivalent to 240.28 Wm􀀀2, 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 MJm􀀀2day􀀀1) equivalent to 198.03 Wm􀀀2. 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 MJm􀀀2day􀀀1 equivalent to 4243.30 Wm􀀀2. The study shows that solar radiation levels over the country (17.11 MJm􀀀2day􀀀1 to 20.76 MJm􀀀2day􀀀1), meet the international solar technology market standards of 18.7 MJm􀀀2day􀀀1 to 20.7 MJm􀀀2day􀀀1 for the operation of photovoltaic systems and solar collectors for industrial and domestic applications.
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,