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Assessment of the solar radiation potential of the Thika and Nairobi area

NW Wasike, TN Soitah, SM Waweru, FN Kariuki

Abstract


This assessment seeks to provide information on the solar energy resource potential of the Thika – Nairobi area essential in the dissemination of Renewable Energy Technologies which are essentially solar photovoltaic and thermal systems. To achieve this, solar radiation data for three stations (Dagoretti Corner, Thika and Jomo Kenyatta International Airport (JKIA) has been collected and analyzed with the aim of assessing the solar radiation potential. The Thika station is at an altitude of 1500 m above sea level and located at (0°, 37° 41' East). Dagoretti Corner station is at 1795 m above sea level and at (01° 18' S, 36° 45' E). The JKIA station is at 1624 m above sea level and at (1° 19’ S, 36° 55' E). The longitudinal and latitudinal difference between these stations is small and that shows how close the stations are to one another. This facilitated the ease of comparison and categorization of the two regions. Data was collected using two instruments: the Gunn – Bellani and the pyranometer. The Gunn – Bellani registers radiation in terms of the amount of liquid distilled, whereas the pyranometer used registers solar radiation in terms of counts. The raw data was first converted to MJ/m2/day and then subjected to quality control procedures. After quality control procedures, the data was analyzed in terms of the average monthly daily insolation. Extraterrestrial solar radiation was estimated using an empirical formula and by using the values of the extraterrestrial solar radiation values of parameters like diffuse solar radiation and clearness index were calculated. Statistical parameters e.g. standard deviation, Skewness and coefficient of variation, were calculated using software to show the variability in the solar energy resource. The analysis shows that the study area has reliable solar energy resources with little variability. The average monthly daily insolation ranges from 3 kWh/m2/day to 7 kWh/m2/day. The national average of 4 – 6 kWh/m2/day from earlier studies falls within this range. The transparency of the sky estimated by the formula KT = H/Ho is also encouraging as it shows that there is little obstruction to the solar radiation. Diffuse solar radiation levels are also high and this shows that incase of obstruction, the diffuse solar radiation can be relied on. The abundance of the resource shows that it is feasible for applications of both solar photovoltaic technologies and solar thermal technologies.

Key words: Insolation, declination, extraterrestrial, photovoltaics




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