Egypt as a developed country still has no electricity in many villages but at the same time has enough natural energy such as solar energy. Solar radiation data is not always available in many areas of the world and they have to be estimated using some sort of empirical model. The results of this prediction are compared for the measured data of two different countries: Japan (Okayama City) and Egypt (Giza City). The comparison shows an acceptable level of prediction between both of them. On a June day, actual accumulated insolation through one day was 18.88 MJ/m2 in Okayama and 22.79 MJ/m2 in Giza. On the other hand on a January day, actual accumulated insolation through one day was 4.93 MJ/m2 in Okayama and 5.49 MJ/m2 in Giza. We can see also that in January the worst solar month, solar water heaters still provide 35.25% of the energy for Okayama and 40.37% for Giza, That was because in Okayama the number of sunny days was only 6 but there were 19 in Giza.