Abstract
In this work, hourly measurements of global solar irradiances obtained from a pyranometer and direct normal irradiances obtained from sunshine duration sensor are assessed through an extensive quality control procedure and statistical analysis on the measured and derived solar parameters for a semimountainous location using data from the last fie years (2016-2020). This information and the method suggested concerning the solar energy capture systems and energy efficiency is useful for engineers who can therefore take knowledge of the local radiation levels. Furthermore, the direct horizontal irradiance canbe easily calculated and the diffuse component can be estimated from the difference of global and direct horizontal irradiances. Monthly mean hourly values of the radiation components are also estimated and shown through isolines diagrams. Representative values of global direct and diffuse irradiances for different times of the year and different hour of the day can be easily read from these diagrams. Simultaneously, a similar analysis is carried out over various solar indices estimated on both an hourly and daily basis. The derived solar indices are the clearness index for global, direct, and diffuse radiation as well as the diffuse and direct fractions from global radiation. The interrelationships between the said indices are also examined.Additionally, the BRL (Boland-Ridley-Lauret) diffuse fraction model which is a multiple predictor logistic model was tested and can be used to estimate the diffuse and later the direct radiation component. The model is a function of clearness index (kt), the apparent solar time (AST), the solar altitude (αs), the daily clearness index (KT) and persistence parameter ψ which is an average of both a lag and lead of the clearness index. The outcome of the model shows that it can be used to estimate successfully the diffuse radiation.

Key words: quality control of solar radiation, solar radiation indices, statistical analysis, isoline diagrams, modeling diffse radiation