The comparative study of the solar powers between two main cities of Chad is performed in the present work, the city of Mongo in the Centre and that of Pala in the South, with an aim of knowing which one of the two cities is more adequate for an installation of the solar power station, taking into account the regional climatic and environmental conditions of both cities. To do this, the graphical statistical analysis of long-term solar irradiance data and temperature is performed. The data used is that of the decade (2010-2020), based on solar radiation data handed by the National Aeronautics and Space Administration (NASA) and Photovoltaic Geographical Information System (PGIS) for Mongo in the centre and Pala in the south of Chad. The shape of the mean monthly irradiation has been plotted and has been approximated using the sinusoidal function through the mean square analysis. The temperature data has been also obtained by the same process and plotted versus irradiance in order to find the adequate mathematical relationship between them. For the statistical analysis, the maximum entropy principle has been used. As results, it is found that the maximum irradiance is obtained in March, which are 226.26kWh/m<sup>2</sup> for Pala and 219.355kWh/m<sup>2</sup> for Mongo, while the minimum irradiances are obtained in August, which are 151.67kWh/m<sup>2</sup> for Pala and 158.9kWh/m<sup>2</sup> for Mongo. The temperature data is also obtained and the mean monthly data plotted, showing that apart for the months of March and April, the the shapes of irradiation and temperatures are similar for both sites. Then it is found that the frequency and probability density distributions reach their maximum at the same dates.