A prerequisite to the sizing of stand-alone photovoltaic power sources is the availability of radiation data at the required location. Generally this is not available for isolated regions. rn Sudan, radiation data are only available for a limited number of stations throughout the country. The present paper validates the clear sky model for predicting solar radiation for parts of the country north of latitude 10 degrees N. The model is used to obtain the hourly global radiation incident on a tilted solar array at any location in that part of the country. A computer-aided sizing program for stand-alone photovoltaic systems was then developed The effects of maximum cell temperature and different load profiles in the system size are investigated.