Solar Energy Collection With A Clear View

Lansing, MI – A team of researchers at Michigan State University has developed a new type of solar concentrator that when placed over a window creates solar energy while allowing people to actually see through the window.

It is called a transparent luminescent solar concentrator and can be used on buildings, cell phones and any other device that has a clear surface.

And, according to Richard Lunt of MSU’s College of Engineering, the key word is “transparent.”
Research in the production of energy from solar cells placed around luminescent plastic-like materials is not new. These past efforts, however, have yielded poor results – the energy production was inefficient and the materials were highly colored.

“No one wants to sit behind colored glass,” said Lunt, an assistant professor of chemical engineering and materials science. “It makes for a very colorful environment, like working in a disco. We take an approach where we actually make the luminescent active layer itself transparent.”

The solar harvesting system uses small organic molecules developed by Lunt and his team to absorb specific nonvisible wavelengths of sunlight.

“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,” said Lunt.

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. Because the materials do not absorb or emit light in the visible spectrum, they look exceptionally transparent to the human eye,” said Lunt.

Last year, GreenActionNews reported on research at MIT in the development of ‘solar windows,’ a project Lunt was a part of as a postdoctoral student. The MIT research demonstrated transparent PVs where the solar cell itself is transparent. “Any time you scale up a PV technology you have to focus on resistive losses (transporting the electricity over large areas), defect tolerance, and cell patterning so that the efficiency does drop somewhat as you make the modules larger,” said Lunt.

“Our new work [at MSU] is actually a parallel approach [to the MIT research],” said Lunt. “With this new concentrator approach, the large area harvesting is done optically, so we have very high defect tolerance, the fabrication becomes much simpler, and for many of our designs, the efficiency actually increases as we scale up. We see these two technologies as complimentary and being deployed in various applications depending on the demands in efficiency, cost, and aesthetics,” said Lunt.

One of the benefits of this new development is its flexibility. While the technology is at an early stage, it has the potential to be scaled to commercial or industrial applications with an affordable cost.

“It opens a lot of area to deploy solar energy in a non-intrusive way,” Lunt said. “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.”

Commercially available PVs which are not transparent have a 10-15% rate of effciency and the highest efficiency colorful luminescent solar concentrator is around 7%. Some solar PVs have a solar conversion efficiency of 38-47%, but these versions as so cost-prohibitive that they are only useful to space exploration applications.

“Because we use so little of the expensive PV material, our technology can be very low cost compared to typical PVs despite the lower efficiency. Ultimately, efficiency is not as important as either the levelized energy cost or the actual power requirements for particular devices,” said Lunt

Lunt said more work is needed in order to improve its energy-producing efficiency. Currently it is able to produce a solar conversion efficiency close to 1 percent, but noted they aim to reach efficiencies beyond 5 percent when fully optimized. The best colored LSC has an efficiency of around 7 percent.

The researchers have a founded Ubiquitous Energy, which is working on commercializing these technologies. Lunt said, “We hope to see these applied in buildings, mobile electronics, and beyond within the next 5 years.”