An extensive statistical analysis of hourly, daily and monthly measured solar radiation has been performed for a site in the northwestern part of Turkey, leading to statistical models. These models are equally applicable in any part of the world with reassessment of the model parameters. The necessary physical interpretations of the model parameters and their temporal variations are also presented. Once these models are established for the site, then it is possible to evaluate the temporal solar radiation amounts by entering the month of concern in a year. The models appear in the form of parabolic equations with three parameters. Significant relationships between these parameters are also shown. It is possible to estimate monthly average hourly global or diffuse radiation amounts by using these equations.