Wavelet power spectrum (WPS) techniques were used to evaluate the temporal structure of the clearness index and relative sunshine duration, using monthly values of clearness index and relative sunshine duration between 1995 and 2010. The significant years are featured by high wavelet coefficients of both the clearness index and relative sunshine duration. Low wavelet coefficients noticed during the selected years might emerge from the increase in turbidity and cloudiness, indicating that cloudiness has the greater impact on the solar radiation resulting in weak sky condition. Bootstrap method was also used to acquire regression correlations between clearness index and relative sunshine duration. The correlation coefficient between the monthly values of clearness index and relative sunshine duration for ABK (0.32), ENU (0.31), JOS (0.40), MAID (0.46), OWE (0.25), PH (0.46), SOK (0.65), YOL (0.58). The climatic condition and weather patterns of locations have an impact on the amount solar energy received.
