Since the solar radiation is the main input for sizing any solar system, it will be necessary to understand and evaluate the insolation data. The horizontal global insolation data have been measured since May, 1982 and direct normal solar insolation data since December 1990 at 16 different sites all over the country and considerable effort has been made for constructing a standard value from measured data at each station. In the results, the average global total solar radiation of the nation is $3,055kcal/m^2.day(12.79MJ/m^2.day)$ and the average clear day direct normal solar beam radiation was $4,600kcal/m^2.day(19.26MJ/m^2.day)$, which indicates possible solar energy application of medium and high temperature technologies with high concentration.