Wind Patterns over a Heliostat Field

Heliostats constitute a major portion of the direct costs of a concentrating solar power tower plant. As a result, a significant amount of effort is being focused on designing and developing cheaper heliostats. The optical and structural performance of these new and existing heliostats under dynamic wind loads must be characterized and understood in order to meet both cost and performance objectives. This paper presents the second phase of a U.S. DOE-sponsored program at Sandia National Laboratories’ National Solar Thermal Test Facility (NSTTF) that includes dynamic testing and analysis of multiple full-scale heliostats. The objectives of these tests and analyses are to characterize and understand some differences in the impacts of dynamic wind loads on heliostat strain and cyclic fatigue between perimeter and inner-field heliostats.A weather tower with three tri-axial ultrasonic anemometers has been erected just outside the field to measure the approaching boundary winds, while a portable tower was set up to characterize wind velocities and turbulence between subsequent rows within the field. Anemometers have also been mounted to some heliostats to gather close range measurement of turbulence and wind frequencies and to provide a point of comparison for computational fluid dynamics models of wind flow over the field.This paper presents mean wind speeds and wind loads on heliostats as a function of field position. The calculated mean wind loads were used to assess the mean wind-load reduction correlation of Peterka [1].