Direct Normal Irradiance and circumsolar radiation: modelling, measurement and impact on Concentrating Solar Power

Abstract

This work aims to model the direct beam and circumsolar irradiance as a function of relevant variables (aerosol optical depth - AOD, relative humidity - RH, precipitable water - W, ozone abundance) and the aperture angle of either pyrheliometers used for measuring the Direct Normal Irradiance (DNI), or solar concentrators. Since pyrheliometers and concentrated solar power (CSP) systems can have different aperture angles, it is not secure to assume that the total amount of Direct Normal Irradiance (DNI) measured by the pyrheliometer is the same that reaches the receiver of a CSP system. The magnitude of the circumsolar irradiance and its distribution around the solar disk strongly depend on the atmospheric components, which vary from place to place and in time. Therefore, the determination of the circumsolar radiation is highly important in order to model CSP systems and to prevent errors in estimating its energy output. Here, the first results are presented regarding the circumsolar irradiance modelling, including the effect of the aerosol optical depth, relative humidity and precipitable water.