DNI and slant path transmittance for the solar resource of tower thermal solar plants: The validation of the ASoRA method and impact in exploiting a global data set.

• The ASoRA method estimates the atmospheric attenuation in a tower CSP. • The atmospheric attenuation occurs in the atmospehric column and in the slant path. • ASoRA is validated with data observed at Ouarzazate, Morocco. • The aerosols are assumed to lie in a surface layerwith a height varying with time. • A reanalysis data set is tested to show the efficiency of ASoRA in its global mode. • The estimated annual average of the solar resource parameters is given for Ouarzazate in 2014. The ASoRA method consists in estimating the solar resource in tower concentrated solar plants by exploiting global data sets. The solar resource parameters are not only the Direct Normal Irradiance (DNI) but also the slant path transmittance (T sp). The column to surface-level conversion process was validated by comparing the retrieved aerosol extinction coefficient (AEC) to independent measurements performed by a ground-based nephelometer. The Aerosol Robotic NETwork (AERONET) provided column-integrated aerosol extinction properties. The European Centre for Medium-Range Weather Forecasts Reanalysis Interim boundary layer height was used to reproduce the seasonal dependence of the aerosol vertical profile. At the daily resolution, ASoRA reproduced observed AEC with a relative root mean square difference (rRMSD) of 33% and a correlation coefficient of 0.90. The spectral extrapolation from monochromatic measurements to the solar broadband was validated by comparing computations and observations of DNI. ASoRA was also able to reproduce the hourly variability of DNI observed by a pyrheliometer with a RMSD of 38 W/m2, a rRMSD of 4.6%, and a correlation coefficient larger than 0.98. Despite larger uncertainties caused by using Modern-Era Retrospective analysis for Research and Applications (version 2) instead of AERONET, the annual average of T sp was underestimated by only 0.01, and the annual average of the irradiance loss in the slant path by only 4 W/m2. Largest impact on T sp comes from the parameterisation of the aerosol vertical profile, and the annual average of T sp was 0.945 at Ouarzazate (Morocco) in 2014, with an estimated uncertainty of 0.030. [ABSTRACT FROM AUTHOR]