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Abstract: This paper quantifies the very short-term variability of the total solar irradiance and the ultraviolet erythemal irradiance (UVER) averaged over 1-min intervals at Granada (Southeastern Spain). A statistical analysis for a four-year period (January 2006–December 2009) under different cloudiness and characterized by the amount of cloud cover (oktas) retrieved from an All-Sky Imager located next to the radiometers is presented. Very short-term variability of the total solar irradiance was larger than UVER fluctuations under cloudy conditions (above three oktas), in accordance with previous works found in the literature. Nevertheless, for cloud cover bellow three oktas the opposite was true; the median relative 1-min fluctuation was larger for UVER than for total solar irradiance. Moreover, while the coefficient of variation (CV) for UVER presented a clear dependence on the solar zenith angle (SZA) under completely cloud-free conditions (from 1.5% for SZA = 20° to 9.5% for SZA = 65°), the CV of the total solar irradiance was under 1.3% with a more stable behaviour for the entire range of SZA. Large differences were found for cloud cover of seven oktas, where the median diurnal 1-min variability for total solar irradiance was 3.9% min−1 compared to 2.5% min−1 for UVER data. Additionally, an episode with surface total solar irradiance higher than its corresponding extraterrestrial value is analyzed. [Copyright &y& Elsevier]

Many Total Solar Irradiance (TSI) and Solar Constant (SC) values are given and used in the literature, sometimes leading to confusion. The TSI value is relevant and has great importance in engineering and scientific research in energy. In this study, a review has been done to study the TSI and SC concepts. A reevaluation of the TSI and SC is undertaken to consider state of the art. The effect of three different TSI values concerning different locations is studied for estimating global radiation with the Ångström-Prescott (A-P) formulation over Spain. New seasonal A-P coefficient sets are developed for Spain. The good performance for all the 29 stations and seasons and the slight differences observed for the different TSI values employed ensure global solar radiation (GSR) accuracy with the A-P model. The results highlight the local and seasonal A-P coefficient calibration relevance instead of using a single general pair of calibration coefficients. Based on the TSI study, we recommended calculations of solar radiation models to adopt the TSI value equal to 1361 W m−2. The revised TSI is lower than the previous values proposed. Therefore, it is highly recommended to review the value and concept of TSI. • A lower Total Solar Irradiance than the previous one is proposed. • High accuracy and precision are needed in environmental research and practice. • New seasonal A-P coefficient are provided over 29 meteorological stations. • A-P coefficient calibration should be considered instead of using a single pair. [ABSTRACT FROM AUTHOR]