A Closed-Loop Heliostat and Tracker System

Abstract

Heliostats are adjustable mirrors used in concentrated solar power (CSP) plants that simultaneously focus solar light on a receiver where steam is produced to power a turbine and generate electricity. Most CSP fields use open-loop systems, relying on astronomical data to adjust the position of the heliostats. However, closed-loop heliostat systems can be used to improve the accuracy and efficiency of heliostats. This article presents the design and implementation of a closed-loop heliostat consisting of a solar tracker that detects the location of the sun, an automated mirror that reflects the light to a target, and a receiver that acts as a locating beacon for the mirror and target for the reflected sunlight. The solar tracker's algorithm uses feedback from four lux sensors to find the azimuth and zenith angles of the sun; it then sends information about those angles to the mirror, which uses those inputs to reflect the light at the target. To improve the precision of the system, a cap was added to the solar tracker, which blocks sunlight unless the rays are normal to the lux sensors within 0.1 deg. Limit switches and proximity sensors were added to both the mirror and the tracker to decrease error accumulation over time using a homing sequence. Upon construction of a prototype, the integrated system was tested, and light was focused within an azimuth offset of 0.16 deg ± 0.1 deg and a zenith offset of 1.84 deg ± 0.16 deg from the expected target.