This work proposes a step-by-step data gathering and processing methodology of solar irradiance measurements for producing filtered and continuous data series for the assessment of solar energy availability. The method is applied to data from 8 measuring stations in the southern region of Portugal. With the current amount of stations and as the measurement period continuously increases, it allows a better regional characterization of DNI availability and creates conditions for in depth studies. This infrastructure has high relevance for the region, known for its high annual GHI availability and its reduced inter-annual variability, thus a high annual DNI availability is expected. The proposed step-by-step data processing methodology includes a comprehensive set of data filtering, gap filling, and QC procedures based in both physical limits and statistical analysis. An extra QC check, with basis on daily totals, is proposed. The results obtained with the proposed methodology are analyzed and discussed; the results are used for the assessment of mean yearly DNI availability for the region. It is expected that this effort will significantly help to realize the region high potential for the development and implementation of Concentrated Solar Power plants, with annual mean DNI availabilities ranging from 1918 to 2097 kWh/m(2)/year. (c) 2020 Elsevier Ltd. All rights reserved.