Closed-Loop Pointing Feedback for Heliostats in Concentrating Solar Power

Abstract

Concentrating solar power (CSP) facilities need to ensure alignment of all sun-tracking heliostats onto the sunlight receiver. A method is proposed to keep all heliostats in a CSP facility under closed-loop pointing control while also providing feedback on the detailed alignment of the segment mirrors of each heliostat. The method is based on the sunlight directed toward the receiver, and thus works under full operational conditions and without the need of secondary optical alignments. It is based on retroreflectors (“retros”) to simultaneously return samples of the sunlight reflected by each mirror back to that same mirror. It goes beyond previous efforts at using retros by placing them into the concentrated sunlight, instead of in its periphery. Quartz glass will be used for its heat tolerance, and reflectivity modulation for visibility is achieved by rotating the retros. The technology can be retrofitted into existing CSP facilities to improve operational efficiency, and it can be used to relax the stability requirements of heliostats, and thus their cost, in the planning of new ones.