Determination of hourly direct normal solar irradiance (DNI) received during an average day of each month is essential for calculating the solar concentrator performance throughout the day. DNI data provided by different databases, spatial or ground-based measurements. While the spatial databases are a useful tool in renewable energy applications, they present uncertainty; the ground-based measurement databases are rarely available at the location of interest because the reasons of high cost and maintenance problems especially for developing countries like Algeria. This lack of DNI data contrasts with the availability of global and diffuse horizontal irradiation data (Gm, DHI). In this study, as the first part of the work, a simplified methodology for estimation the hourly, monthly and annual direct normal irradiance DNI data using the monthly mean global and the diffuse horizontal irradiance (GEH, DHI) is presented. Secondly, the data of the modeled DNI in addition to NASA-SSE database are validated their uncertainties using nine statistical parameters, and by comparison with the measured data of three ground stations in Algeria (Algiers, Ghardaia and Tamanrasset).