Wind loads on heliostats and photovoltaic trackers of various aspect ratios

Abstract

For the layout of solar trackers the wind loads on the structure have to be known. They can be calculated by using wind load coefficients given in literature. But so far these values are only valid for aspect ratios of the panel (width to height) of about 1.0. Therefore the wind load coefficients for heliostats of aspect ratios between 0.5 and 3.0 were determined to close this gap. As solar trackers are exposed to the turbulent atmospheric boundary layer the turbulence of the approaching flow has to be modeled. As a reliable method at reasonable cost wind tunnel measurements were chosen. Solar trackers of 30 m2 panel size were investigated at a model scale of 1:20. Wind direction and elevation angle of the panel were varied to investigate especially the constellations at which the highest wind loads are expected (critical load cases). By spires and roughness elements a wind profile and a turbulence intensity of the modeled wind according to typical sites for solar trackers were achieved. The loads were measured by a high frequency force balance placed underneath the models. Additionally measurements of the pressure distribution on a panel with aspect ratio of 1.2 were performed to better understand the effects that lead to the peak values of the wind load coefficients. A significant impact of the aspect ratio was measured. For the critical load cases the aspect ratio dependencies of the accordant peak wind load components were determined. By these the peak wind loads on solar trackers of varies aspect ratios can be calculated. Regarding the single solar tracker components the main results are: Higher aspect ratios are advantageous for the dimensioning of the foundation, the pylon and the elevation drive but disadvantageous for the azimuth drive.