Modeling of Irradiance Attenuation from a Heliostat to the Receiver of a Solar Central Tower

Abstract A test bench located at Jabal Hafeet Mountain in Abu Dhabi has been prepared. Four pyrheliometers located at different altitudes from 340 m to 1035 m above mean sea level continuously recorded the Direct Normal Irradiance (DNI) with high accuracy. From the analysis of these measurements, a model simulating the attenuation of direct irradiance with distance of propagation, within 100 m above the surface (approximate height of a tower) was designed. A general shape of the relationship between the atmospheric optical depth from the top of the atmosphere to the ground reference and the extinction coefficient of the irradiance from the ground reference to the target was derived and validated with the use of ground measurements. This relation was used to estimate the DNI at two stations with mean path of sunlight from the reference station equals to 0.3 km and 0.6 km respectively. The comparison of the estimated and measured DNI at these two stations resulted in favorable bias and standard deviation values (bias of 0.3% and 0.4%, and standard deviation equals to 6% and 8% for the two stations respectively). Additionally, the applicability of this method in other locations was discussed.