Assessment of the Solar Radiation Potential of the Thika-Nairobi Area, Panel Sizing and Costing

Abstract

Kenya lies astride the equation and therefore receives allot of sunshine. Being a renewable energy source, its supply is abundant. The major problem in the exploitation of the resource is lack of or inadequate data on the available insolation. Several researches have earlier been conducted, but a closer scrutiny reveals that the data they used had missing values and hence empirical formulae had to be employed in filling the missing values. In the dissemination of solar technologies and most commonly solar photovoltaic systems, vendors/dealers in these fields do estimates without making reference to the available insolation. It should also be noted that there is no national data base for storage of insolation information.A detailed knowledge of solar radiation is essential for its application. Research done should rely on data that has been collected consistently for a long period of time. Estimation of photovoltaic system should rely on the findings done in those researches. So long as data collection is continuous, the analysis of the available insolation should also be continuous.This study aimed at evaluating the insolation available in the Thika- Nairobi area for purpose of solar panel sizing and costing, in consideration of increased power demand in Kenya and the increase in the cost of conventional energy resources. Data was collected at Thika agro – meteorological station, Dagoretti corner station and the JKIA station for duration of six months. The three stations lie in the same geographical location. Data was collected using the Gunn – Bellani and the pyranometer. To get more meaningful trends and validation of data, historical data for the three stations was considered. The data was analyzed in terms of the average monthly daily insolation and average annual daily insolation. Angles of declination were calculated and the extraterrestrial solar radiation values were found to be 10.14 MJ/m2/day for Dagoretti Corner, 10.13 MJ/m2/day for both JKIA and Thika. Average annual daily diffuse solar radiation for all the stations range between 6 – 8 MJ/m2/day. The average monthly daily diffuse solar radiation was found to be: Dagoretti corner, 6 – 8 MJ/m2/day; Thika, 6 – 8.5 MJ/m2/day and JKIA station, 7 – 8.5 MJ/m2/day. The clearness index lay between 0.4 and 0.7. Percentage contribution of the diffuse solar was also calculated. Statistical parameters were calculated using SCC stat. From the analysis, it was concluded that the average annual daily insolation range from 4 – 6 kWh/m2/day and the average monthly daily insolation range from 3 – 7 kWh/m 2/day. These values have a larger range with the maximum value being 1 kWh/m2/day higher than the predicted values of which range 4 – 6 kWh/m2/day and these shows that the region is endowed with enough insolation for solar energy application. The results have been further applied in the sizing and costing of solar systems.