Estimation of Clearness Index and its Application in Determining Sky Conditions using Three Cities in Ghana as a Case Study

Abstract

In this work, hourly global radiation and extraterrestrial data for three locations in Ghana, namely Accra, Kumasi, and Navrongo, were used to estimate the daily clearness, monthly mean clearness index, and monthly-averaged hourly clearness index of the study areas. It was observed that the monthly average clearness index of Accra ranged from 0.4505 to 0.6975 and that of Kumasi and Navrongo varied from 0.4553 to 0.6908 and 0.4529 to 0.6949, respectively. There was no overcast sky in the year 2018 for all the three study areas in Ghana, and approximately two-thirds of the year’s day length experienced clear-sky conditions. Partly cloudy conditions were predominant in the wet season of the year.