Hybrid daylight harvesting system using static ball lens concentrator and movable optical fiber

Abstract

We demonstrate a prototype for a compact, hybrid daylight harvesting system that collects and transports sunlight to illuminate dark spaces, up to two levels underground. The prototype is designed to have a compact size so that it can be mounted on top of a conventional lamp post at ground level and the system serves an additional purpose of a streetlamp for ground level illumination during nighttime. The system utilizes an acrylic ball lens as solar concentrator, and the focused sunlight is directly coupled into a single plastic optical fiber that transports it to indoor spaces. The spherical symmetry of the ball lens allows it to be static, while the position of focused light spot varies gradually underneath it, in accordance with the solar position in the sky. Therefore, only the light-collecting optical fiber needs to be moved under the ball lens, obviating the need for heavy-duty motors typically used to align solar concentrators along the direction of sun’s rays. The focused sunlight under the ball is tracked using a microcontroller-based tracking mechanism. This design is the first demonstration of a daylight harvesting system, to the best of our knowledge, using a ball lens as static sunlight collector and a movable optical fiber tracking the focused spot underneath the ball. The moving parts in the proposed system are lightweight and are well concealed from environmental hazards like dust, wind and moisture.