Distribution of hourly variability index of sky clearness

Clouds affect the values of insolation for solar technology and other applications. To detect the presence of variability in the sky clearness, an hourly variability index (p3) is calculated. The present study examined the frequency distribution of this variable as a tool for assessing the utilizability of solar radiation at a site. Solar radiation data from Chileka weather station in Malawi was used to calculate p3 and mean monthly variability index (p3m) and determine the probability model for each month. It was found that p3m was highest in April (0.20) and lowest in September (0.10), with the beta probability model fitting most of the monthly data satisfactorily. It appears that the site has great potential for application of solar technologies.