Evaluating Solar Radiation Attenuation Models to Assess the Effects of Climate and Geographical Location on the Heliostat Field Efficiency in Brazil

AbstractMost of the solar power plants using a central receiver which are currently in operation are installed in the Sun Belt region, specifically above the Tropic of Cancer. These plants are located in regions characterized by a dry summers and a yearly sum of Direct Normal Irradiation (DNI) of over 2300 kWh/m2. These regions include the Mojave Desert (semi-arid climate) and Andalucía in southern Spain (Mediterranean and semi-arid climate). Potential locations for installing such plants in Brazil, identified in previous studies, are the São Francisco river basin and the Sobradinho area in the Northeast Region of the country. These locations are characterized by high humidity levels and yearly DNI values ranging from 1800 to 2300 kWh/m2, which is in clear contrast with the dry and desert climates where the solar tower projects currently in operation are located. Besides the combined effects of climate and the inter-tropicalization of the site, based on the solar angles and atmospheric attenuation, the potential locations in Brazil provide a small variation between the monthly averages DNI values. In this paper, the effects of these particularities on the performance of a heliostat field are assessed. For instance, the effects of the atmospheric water vapor and aerosol concentration on the optical performance of the heliostat field are analyzed. The results suggest that, for the same DNI level, the heliostat field in Brazil should be 4% larger due to the effect of the water vapor concentration in the atmosphere. This is an important finding, which shows that the current models for calculating the attenuation between the heliostat and the receiver need to be reviewed and compared with experimental observations and validated for the conditions prevailing at potential locations in Brazil