摘要： The solar radiation needed for effective research into solar energy utilization can be determined using concise and reliable data which can be gotten from hourly or daily data. The parameters which govern a physical model of the sky should be taken hourly or daily. The values which fluctuate according to the fluctuating changes in the meteorological and environmental situations should be analyzed with data over a short period of time. These parameters include the sunshine hours, Solar radiation, cloud cover, temperature etc. In predicting the performance of solar energy conversion devices, a sequence of daily radiation is always required. The daily data are not readily available, hence, there is need for the derivation of the needed, which is the daily solar radiation data from the available- the monthly averages. For many stations in Nigeria, only monthly long-term averages are available and the problem of extracting reliable information always sets in. Therefore, this paper proffers solutions to this by establishing a procedure for the derivation of daily solar radiation from the monthly averages using Fourier series.