Transparency-Switching Optical Element for Reactive Sun Tracking

Abstract

Concentrated photovoltaics (CPV) are a major potential growth area in photovoltaics technology, allowing the use of high-performance solar cells in a cost effective way by using inexpensive optical elements to concentrate sunlight onto a reduced cell area. CPV penetration into commercial markets has been limited by the need for sun tracking, an unavoidable consequence of the thermodynamic principle of étendue conservation. As tracking is presently accomplished by the use of bulky and expensive mechanical trackers, small-scale CPV installation, in particular the large rooftop PV market, remains practically and economically unfeasible. However, through dynamic variation of the optical properties of the collector, it is possible to achieve fully non-mechanical sun tracking over a wide angle. This thesis describes a ‘self tracking’ system that is both non-mechanical and reactive (i.e. activated only by the variations in the solar angle and requiring no external control), based on a transparency-switching material. When illuminated by a focused light beam, the normally opaque material is able to form a localized transparency that remains centered on the focal spot if the spot position is varied. This behavior is used to create a light-responsive moving input aperture for a light-trapping concentrator. The concentrator operating principle, material characterization and physics, theoretical consideration of the required optimizations and an experimental demonstration on the sun-tracking capability will be presented.

Date of Award	May 2015
Original language	American English
Supervisor	Matteo Chiesa (Supervisor)