A solar concentrator you can see through

Researchers from Michigan State University (MSU) have developed a solar concentrator which, when placed over a window, creates solar energy while allowing people to actually see through the window. The device - a transparent luminescent solar concentrator (TLSC) - can potentially be used on any object that has a clear surface.

Research into the production of energy from solar cells placed around luminescent plastic-like materials is not new; however, energy production has so far been inefficient and the materials have been highly coloured. According to Richard Lunt, an assistant professor at MSU’s College of Engineering, “No one wants to sit behind coloured glass.”

“We take an approach where we actually make the luminescent active layer itself transparent,” said Lunt, whose team developed small organic molecules which absorb specific non-visible wavelengths of sunlight. He stated, “We can tune these materials to pick up just the ultraviolet and the near infrared wavelengths that then ‘glow’ at another wavelength in the infrared.”

A transparent luminescent solar concentrator waveguide, with colourful traditional luminescent solar concentrators in the background. Photo by GL Kohuth.

The ‘glowing’ infrared light is guided to the edge of the plastic, where it is converted to electricity by thin strips of photovoltaic solar cells. Lunt explained, “Because the materials do not absorb or emit light in the visible spectrum, they look exceptionally transparent to the human eye.” The research was featured in the journal Advanced Optical Materials.

Currently, the concentrator has demonstrated solar conversion efficiency close to 1%. Lunt said the researchers aim to reach efficiencies beyond 5% when fully optimised. The best coloured LSC has an efficiency of around 7%.

MSU doctoral student Yimu Zhao holds up a transparent luminescent solar concentrator module. Photo by Yimu Zhao. 

The technology has already demonstrated the flexibility to be scaled to commercial or industrial applications with an affordable cost. Lunt suggested, “It can be used on tall buildings with lots of windows or any kind of mobile device that demands high aesthetic quality, like a phone or e-reader.

“Ultimately, we want to make solar-harvesting surfaces that you do not even know are there.”

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