Thin plastic overlayer doubles efficiency of rooftop solar panels
While the latest commercially available rooftop solar panels boast conversion efficiencies around the 18 to 20 percent mark, there are solar cells capable of achieving efficiencies of over 40 percent. So why aren't these making their way onto roofs? The answer is cost. But that could be about to change with Swiss startup Insolight developing a thin plastic layer that sits atop a panel and directs the sun's rays to a small area of very high performance solar cells.
While some researchers are devoted to improving the efficiency of solar cells themselves, other efforts to increase energy output involve developing systems that focus as much sunlight onto the cells as possible. But the efficiency is still dependent on the solar cells' performance, while existing concentrators can be cumbersome and need to constantly be repositioned to reap their full benefits.
Insolight's strategy was to use some of the highest rated solar cells already available, which yield 42 percent efficiency by capturing different wavelengths of light. These cells are prohibitively expensive for all but special uses, notably in aerospace, so to keep costs down the company only uses small numbers of the super cells.
They then turned to the issue of how to concentrate the sunlight hitting the cells and developed an injection-molded plate arrayed with plastic bubble lenses that act like a network of tiny magnifying lenses. These focus the light hitting the panel onto segments of the solar cells that are only several square millimeters in size.
"It's like a shower: all the water goes down one small drain, there's no need for the drain to cover the entire floor of the shower," says Laurent Coulot, Insolight's CEO.
The plate is attached to a metallic frame that moves just several millimeters throughout the day, guided by a sensor that tracks the sun's position. As a result, this micro-tracking system is able to capture 100 percent of the sunlight regardless of the angle of the sun, which can prove especially important for higher latitudes.
The Fraunhofer Institute in Germany has independently validated performance of a prototype, which Insolight claims achieved a yield of 36.4 percent, or roughly double that of traditional solar panels for the same footprint – which the company says, "is a potential world record for a flat panel that can be mounted on a roof."
The prototype with now be subjected to real-world testing and the company is hopeful they could be on the market before too long. This is in large part because the system is already near market ready as it was designed with components that are easily mass produceable. It's also comparable in size to conventional solar panels, and can be installed with standard mounting systems.
The company believes their cells will be a little more expensive than conventional solar panels, "but this will be quickly offset by the additional energy that will be generated," says Florian Gerlich, Insolight's COO.
The company developed their concept with a grant from the Ecole Polytechnique Federale de Lausanne (EPFL) in the Laboratory of Applied Photonics Devices.
The video below gives an overview of the system.