This paper investigates the Weibull distribution analysis for an accuracy global solar irradiance assessment considering period measurements based on several and grouping years. The problem study in this paper is to find a global solar irradiance model in order to provide accurate estimation of PV energy output allowing better sizing of PV installation. The aim is to select the best Weibull fit procedure for obtaining reliable global solar irradiance from sun that incident in a place during time periods to estimate its yearly energy generation from PV plant. Comparisons are carried out between Graphic, Moments and Maximum Likelihood methods with two different databases (real data on-site measurements and SODA website database). These comparisons are made on global solar irradiance frequency distributions and annual solar irradiance assessment for different French locations. The originality of the paper is that the obtained results prove that the Maximum Likelihood method fits better with the global solar irradiance distribution while the Moment method provides an annual solar irradiance prediction. Thereby, we exploit the obtained results from the Moment method to achieve a more accurate solar energy forecasting model. This resulting model can be implemented for providing one solar energy estimation tool for PV plant sites. (C) 2020 Elsevier Ltd. All rights reserved.