Impact of field density on heliostat drag

Abstract

Heliostat design parameters are typically based on wind load estimations derived from isolated heliostats. Heliostats must be configured as an extended array to generate meaningful energy for a Concentrated Solar Power plant. Array based wind loading estimations from literature are not sufficient for industry to tailor a heliostats design based on a location within an array. This study conducted systematic wind tunnel experiments deriving drag coefficients across 7 rows of heliostats using load cells. The experimental setup contains 49 square heliostats arranged in a linearly staggered layout in The University of Adelaide Wind Tunnel. Two heliostat array densities of 12.5 % and 37.5 %, referred to as low-density and high-density arrays respectively, were experimentally tested with the facets normal to the flow. Compared to an isolated case, findings derived from the load cells indicate heliostat drag is overestimated at all locations within an array for densities between 12.5 % and 37.5 %. The overestimation in mean drag coefficient can be up to a factor of 70 % and 98 % in low- and high-density arrays at Rows 3.5 and 4, respectively. For interpretation of load data, flow characteristics approaching each heliostat row were quantified using a multi-hole pressure probe. In-depth analysis of the flow characteristics identified similarities to canopy flow scenarios, with high-density arrays being most similar. The similarity of flow characteristics within heliostat arrays and canopy scenarios is significant as being able to draw upon the vast literature in the field of canopy flow improves the confidence in wind load estimates within an array.