While skylines vary from city to city, they tend to have at least one thing in common – lots of glass. Now imagine there was a way to ‘upgrade’ all of that glass into solar harvesting systems, such that the amount of energy harvested from the exterior of the building is enough to completely power the inside. A team of researchers at Michigan State University led by Dr. Richard Lunt, Assistant Professor in Chemical Engineering and Materials Science, are clearing the way for scalable solar energy harvesting from clear plastic or glass surfaces. While harvesting solar cell energy from luminescent plastic materials is not new, the real breakthrough for Lunt’s team has been making the luminescent active layer transparent. Previous iterations of luminescent solar concentrators (LSCs) were typically made from highly coloured materials. As a result, real world applications were very limited. However, with Lunt’s transparent LSC, the sky is truly the limit.

As Lunt explains, “I grew up just outside Boston and I began to appreciate the amount of area, in not only glass, but just tall buildings in general and there’s often more area in the vertical footprint than there is in the rooftop footprint. One of our thoughts is if we can turn these areas into solar harvesting surfaces, we could really make a big impact.” This is where the transparent luminescent solar concentrator makes all the difference.

Using small organic molecules developed by Lunt and his team, the solar harvesting system absorbs specific 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,” says Lunt. This glowing infrared light is channeled to the edges of the plastic material where it is converted to electricity by thin strips of photovoltaic solar cells. Lunt further explains, “Because the materials do not absorb or emit light in the visible spectrum, they look exceptionally transparent to the human eye.” This is a vast improvement over the concentrator’s colourful predecessors: “No one wants to sit behind coloured glass. It makes for a very colourful environment, like working in a disco. We take an approach where we actually make the luminescent active layer itself transparent.” Lunt actually keeps a bright pinkish-orange example, like the ones from the 1970s, in his office as a reminder and an inspiration.

In addition to eliminating the ‘disco effect’ that plagued earlier solar concentrators, the main benefit of this latest development is the flexibility and multitude of applications it promises. It is relatively inexpensive and can be scaled to commercial or industrial applications. Says Lunt, “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.” And while the cost of photovoltaic cells continues to diminish as interest in the market grows from countries such as Germany and China, the LSC system of harvesting solar energy is still considerably cheaper to implement. Not only can the system be integrated into new construction of buildings or products, it can also be incorporated into a laminate-like film that can retrofit existing structures or products. For example, a building can be retrofitted with LSC laminates from the inside rather than replacing each window.

Future work will be done to improve the concentrator’s energy-producing efficiency. Current solar conversion efficiency is close to 1 percent, but Lunt hopes to reach efficiency levels beyond 5 percent in the near future. The highest performing coloured luminescent solar concentrator has an efficiency of approximately 7 percent. Lunt predicts that the potential impact of this technology could be significant. “In some early simulations that we’ve been working on to look at the impact, depending on the shape and the orientation and the location of the building, it looks like it could be anywhere from 10 to up to 50 percent of a building’s energy demand that you can get in both the electricity and the heat management savings,” says Lunt. Ubiquitous Energy, a California-based company that Lunt co-founded, is currently working on commercializing the transparent luminescent solar concentrator. Lunt suggests it could be on the market within five years.

The work of Dr. Lunt and his team is proof that sometimes the best innovations are not those that showcased with velvet ropes and flashing lights. In fact, some of the best innovations are the ones that can’t be seen at all.

About The Author

John Keirstead
John Keirstead
Serial Entrepreneur, Technologist and Inventor.
My objective is to develop useful products that have a net positive effect in the lives of those that use them and the environment that we live in.
CEO of Mission LED Lighting Company Ltd.

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