Researchers from the Masdar Institute of Science and Technology have developed a novel device that can track and concentrate sunlight onto high-efficient solar cells, without mechanically moving to follow the sun’s path across the sky. This proof-of-concept research is the first step towards the development of a self-tracking concentrating photovoltaic (CPV) system.
“Traditional CPV systems rotate solar panels to face the sun using a mechanical tracker that is both expensive and too big to put on rooftops,” explained Masdar Institute Research Engineer Harry Apostoleris, whose Master’s thesis focused on this work.
“We are trying to accomplish this tracking through a flat system that does not move, by changing only the optical properties of the collector, not its physical orientation,” he added.
Apostoleris is lead author of a paper published on this research earlier this month in the journal Nature Energy with his supervisor, Dr. Matteo Chiesa, Associate Professor of Mechanical and Materials Science Engineering, Masdar Institute, and Dr. Marco Stefancich, Researcher at the National Research Center in Parma, Italy. Their research was awarded an MIT Deshpande Center research grant for its innovative potential.
The team’s proposed sun-tracking system acts like a box – made of an opaque, waxy material made of a silicone and paraffin composite – that employs an optical “hole” on its surface to track the sun’s path throughout the day. As the sun’s infrared and visible light enters the hole on the box’s surface, the reflected rays are blocked when they try to escape and are utilized by high-efficiency PV cells.
The hole is created by focusing sunlight onto a single spot, which becomes transparent when hit with concentrated light, allowing the sunlight in. The box’s material is opaque when cold and transparent when hot. Thus, by focusing light onto the material, a small transparent region is created.
A lens is placed in front of the box, concentrating and directing sunlight onto a small area of the transparency-switching material, creating the optical ‘hole’ or transparent area. As the sun moves, causing the location of the focal spot to vary, the hole moves so that light can continually enter the device.
Traditional CPV systems reach high light-to-electricity conversion efficiencies – 30% or more – by concentrating direct sunlight onto multi-junction solar cells. These bulky systems track the sun’s path throughout the day with expensive and heavy mechanical systems that rotate as the sun moves. Though, according to a report by IHS Technology, CPV installations have increased by 37% this year, their high costs and weight make them suitable only for utility-scale PV in regions with very clear skies, rendering them essentially absent from the fast-growing distributed PV market.