The use of photovoltaic solar energy is affected by variations in the availability of solar radiation, which creates stability in solar panels. In our case, the need arose to study the temporal variability of solar energy in the southern region of Mozambique. This was followed by a descriptive sequence, applying the analytical method for the classification of days and the analysis of the day’s variability of clear, cloudy and intermediate skies in the data from three regional stations. The results show that it was mostly on clear sky days (44.64%), enhancing the use of solar energy. Statistical analysis of the frequency density variability shows that days with intermediate skies have a similar behavior, however they present a smooth decrease, because for variation of clear sky index ∆Kt* in the interval [-2,2] it is higher. The values of Kt* vary between 0.3342–1.2764, the minimum is observed in the month of July and the maximum in December and the variations during the daily course of the Kt* determined according to its standard deviation show such suitability to the model adopted for the calculation of global irradiation under the clear sky, as an appropriate choice of time interval and amplitude for the study of variations.