Papers by Keyword: Heliostat

Abstract: Solar central receiver or "power tower" thermal energy systems demand high precision heliostat tracking. Large numbers of heliostats in the field need to precisely track their own targets. Such a scenario suggests a hierarchical control architecture in which a model based controller could occupy the supervisory level. A novel two-level control architecture consisting of the NREL SPA (Solar Position Algorithm) and ANFIS (Artificial Neural and Fuzzy Inference System) as supervisory control is presented. The ANFIS system offers reduced complexity and allows for the quick simulation of various heliostat geometries without solving the kinematics. The initial system design, simulation and tracking results using Matlab SimMechanics and Simulink are given here.

Abstract: Flat rectangular heliostats’ surface wind pressure distribution under resting condition was analyzed via wind tunnel experiment results. The flow field characteristics of the mirror in parallel with the ground were combined to reveal the distribution cause of fluctuating pressure. Phenomena of columnar vortex and conical vortex formed from mirror’s flow field under wind angles 0° and 45° were aimed to explain their internal structure using theory of point vortex model. With power spectrum of peculiar points’ fluctuating wind pressure analyzed, the surface vortex characteristics were further elaborated. The above work revealed heliostats’ surface wind pressure characteristics under resting conditions, and established the theoretical basis of its design study.

Abstract: Heliostat is the major part of solar tower power station whose wind resistance is deemed significant in design. The CFD model of single heliostat under typical operating situation was founded by technology of numerical simulation based on standard k-ε model. This paper puts forward a mesh generation method applied to complex projects under different working conditions. The corresponding UDF program was framed & used to simulate proper wind field entry conditions. The wind pressure distributions variation rules at different wind direction & elevation angles got summarized. The drag coefficients, the lift coefficients, and the three-dimensional moment coefficients in wind power coordinate under different operating conditions were computed. The results agree well with experimental data though a little bigger error exists locally. Moreover, the flow field distribution hard to acquire in wind tunnel test was compensated to further explain origin of heliostats wind pressure distribution. The influencing factors and the variation rules discovered reveals that prediction by numerical simulation is practically satisfactory.

Abstract: Heliostat is the key part of Solar Tower power station, which requires extremely high accuracy in use. But it’s sensitive to gust because of its light structure, so effect of wind load should be taken into account in design. Since structure of heliostat is unusual and different from common ones, experimental investigation on rigid heliostat model using technology of surface pressure mensuration to test 3-dimensional wind loads in wind tunnel was conducted. The paper illustrates distribution and characteristics of reflector’s mean and fluctuating wind pressure while wind direction angle varied from 0° to 180° and vertical angle varied from 0° to 90°. Moreover, a finite element model was constructed to perform calculation on wind-induced dynamic response. The results show that the wind load power spectral change rulers are influenced by longitudinal wind turbulence and vortex and are related with Strouhal number; the fluctuating wind pressures between face and back mainly appear positive correlation, and the correlation coefficients at longitudinal wind direction are smaller than those at lateral direction; the fluctuating wind pressures preferably agree with Gaussian distribution at smaller vertical angle and wind direction angle. The wind-induced response and its spectrums reveal that: when vertical angle is small, the background responsive values of reflector’s different parts are approximately similar; in addition, multi-phased resonant response occurring at the bottom. With the increase of , airflow separates at the near side and reunites at the other, as produces vortex which enhances dynamic response at the upper part.