The study of optical characteristic in variable focusing heliostat prototype

Abstract

The heliostat technology has been developed in solar energy utility mainly for the application in the central receiver system and solar furnace. The function of heliostat is to harness the solar energy by reflecting the sunray onto a receiver or second stage concentrator. However, the heliostat remains as a reflector rather than a concentrator for most application. Variable focusing heliostat is a new technique used to concentrate the sunray to achieve high concentration by using single stage reflection. With a different rotational method employed for the sun-tracking operation, the mirror facets can be controlled in groups. In order to achieve higher concentration, mirror distortion method has been studied in this research to come out with a flexible technique for adjusting the focusing distance of single mirror. The design of the mirror attachment also gives flexibility in aligning the mirror during pre-setting process. The image size given by a single mirror can be estimated base on the focusing distance and incidence angle of the sun. A mirror alignment technique by using camera also introduced in this study to ease the complexity of pre-setting the mirror facets.