HARMONIC-ANALYSIS OF MONTHLY SOLAR-RADIATION IN NIGERIA

Monthly solar irradiation data for 28 stations in Nigeria have been applied in a Fourier series and the pertinent amplitudes, phase angles, and harmonic angles have been obtained for each station. The study reveals that the first harmonic is only marginally more dominant than the second one and that between both of them, they account for over 80% of the variance at most stations. The phase angle of maximum radiation of the first harmonic indicates a general tendency to produce a maximum weeks after the vernal equinox, taking generally longer as we move from south to north.