Evaluation of Solar Energy Losses for the Heliostat-To-Receiver Path of a Tower Solar Plant for Different Aerosol Models
Abstract
The efficiency of solar tower plants is impacted twice by atmospheric aerosols. First, aerosols attenuate the direct solar irradiance reaching the heliostats, and then reduce the irradiance reflected by these heliostats while it propagates to the receiver. The aerosol transmittance from the top of atmosphere to the ground is well modeled by many radiative transfer codes, but its counterpart for the heliostat-to-receiver slant path has only been estimated for a very limited number of ideal atmospheric conditions. In this work, the solar losses for the heliostat-to-receiver slant paths are extensively analyzed for different aerosol models, atmospheric conditions, and mirror-to-tower geometries by performing detailed simulations with the MODTRAN radiative transfer code. Reductions up to 30% of the solar irradiance incident on distant heliostats can occur under moderately turbid situations, due to the concentration of aerosols near the ground. It is found that site elevation is not a significant factor, contrary to what was anticipated, according to an old empirical model of the literature.