The Sun is a sphere of intensely hot gaseous matter with a diameter of 1,39×109m(Duffie & Beckman, 1991), which emits considerable solar energy used for various purposes, which flashes along the year. Motivated by the above, the need arose to assess the temporal variability of solar energy in the conditions of Maputo City. To this end a descriptive sequence was followed, to classify the days of the year and analyze the variability of the clear, cloudy and intermediate day, using the analytical method to determine the clear sky index(𝐾𝑡∗), a factor that removes and corrects solar radiation due to solar geometry. The results show that the year 2012, comprised of six (6)moths distributed in all seasons of the yearanalyzed, the frequency density variability has a maximum forthe variation of the clear sky index(∆𝐾𝑡∗)close to zero, and gradually decreases as they grow in absolute value, reaching values below 0.03close to 1.0. Cloudy days have the same behavior although values below 0.02are not reached. The intermediate sky days have a similar behavior to the previous ones, however they present a slight decrease, since for ∆𝐾𝑡∗in the interval [−1;1]it is higher. These results agree with those reported in the literature in Lohmann et. al., (2016)and Perez, Richard et. al. (2016) although this analysis is in terms ofusing the Kernel density magnitude, and based in data of correlated stations. It can be concluded that the values of𝐾𝑡∗for a day vary between 0.3342−1.2764, with the minimum observed in July and maximum in December, and the variations during the daily course of 𝐾𝑡∗determined according to its standard deviation show a good adequacy ofthe model adopted for the calculation of the global irradiation in clear sky, and an appropriate choice of the time interval and period for the study of the variations.

Keyword:Variability, Clear sky index, Solar radiation, Irradiance.