Natalie Hanrieder

Atmospheric Extinction in Simulation Tools for Solar Tower Plants

Atmospheric extinction causes significant radiation losses between the heliostat field and the receiver in a solar tower plants. These losses vary with site and time. State of the art is that in ray-tracing and plant optimization tools, atmospheric extinction is included by choosing between few constant standard atmospheric conditions. Even though some tools allow the consideration of site and time dependent extinction data, such data sets are nearly never available. This paper summarizes and compares the most common model equations implemented in several ray-tracing tools. There are already several methods developed and published to measure extinction on-site. An overview of the existing methods is also given here. Ray-tracing simulations of one exemplary tower plant at the Plataforma Solar de Almeria (PSA) are presented to estimate the plant yield deviations between simulations using standard model equations instead of extinction time series. For PSA, the effect of atmospheric extinction accounts for losses between 1.6 and 7 %. This range is caused by considering overload dumping or not. Applying standard clear or hazy model equations instead of extinction time series lead to an underestimation of the annual plant yield at PSA. The discussion of the effect of extinction in Tower plants has to include overload dumping. Situations in which overload dumping occurs are mostly connected to high radiation levels and low atmospheric extinction. Therefore it can be recommended that project developers should consider site and time dependent extinction data especially on hazy sites. A reduced uncertainty of the plant yield prediction can significantly reduce costs due to smaller risk margins for financing and EPCs. The generation of extinction data for several locations in form of representative yearly time series or geographical maps should be further elaborated.

Sandstorm Erosion Simulation on Solar Mirrors and Comparison with Field Data

Solar reflectors for concentrating solar power applications can be subject to performance losses due to their permanent exposure to the environment. In this work the risk of erosion due to sandstorms is evaluated. Aluminum and glass reflector samples were exposed in Missour and Zagora (Morocco) and measurements of the wind velocity and the particle concentration were carried out. Both measured quantities were connected to the single particle momentum distribution SPMD. This novel parameter is shown to be adequate to describe the erosion characteristics of outdoor sites and laboratory setups. Its deduction will be explained and it will be applied to both outdoor sites and two accelerated erosion simulation setups, a sand trickling device -named soil pipe- and a closed loop wind channel with particle injection. Furthermore different erosion failure modes are described and explained by the use of the SPMD.