Design, fabrication and testing of a multifaceted adaptive-optics, variable-focal-length heliostat

The heliostat field is the critical component of concentrating solar thermal (CST) tower systems for collection of solar radiation. Traditional heliostat designs used in commercial and research CST tower systems can be classified as single-facet heliostats, which employ a single continuous mirror to direct sunlight, and multifaceted heliostats, which use at least two optically aligned (canted) mirror facets to redirect solar radiation onto a receiver. However, these designs face limitations in maintaining optical performance throughout the day, primarily due to astigmatic aberration losses. These losses directly impact CST tower system efficiency. Furthermore, the heliostat field accounts for a significant portion of overall system cost, largely due to the absence of a standardized heliostat design. Without such standardization, each heliostat must be individually canted with high precision based on its field position to accurately aim at the receiver, significantly increasing complexity and cost. This paper explores the engineering design, development and testing of a multifaceted adaptive-optics heliostat, which, on top of the sun tracking capability, allows each facet to independently adjust its orientation to modify its focal length and correct aberration errors. To maintain cost efficiency, the design leverages advances in the broader Internet of Things (IoT) ecosystem, including low-cost microcontrollers, sensors, and actuators/drives, along with inexpensive drives and polymer-based component manufacturing. The testing of the heliostat demonstrated effective astigmatic aberration correction, whereas a detailed cost analysis indicated the potential for such heliostat designs to offer a viable and cost-effective solution for next generation CST tower systems.