A new kind of solar cell could give windows the ability to generate electricity. The polymer solar cells (PSCs), developed by researchers at the University of California, Los Angeles (UCLA) absorb mostly infrared, not visible, light, making them almost 70 percent transparent to the human eye.
The cells are made from a photoactive plastic that converts infrared light into an electrical current, according to an article in ACS Nano that describes the research. Applications could include high-performance, visibly transparent photovoltaic (PV) devices, such as building-integrated PV and integrated PV chargers for portable electronics, said study leader Yang Yang, UCLA professor of materials science and engineering, and director of the Nano Renewable Energy Center at California NanoSystems Institute (CNSI).
A new kind of polymer solar cell that is almost 70 percent transparent to the human eye could give windows the ability to generate electricity by absorbing mostly infrared, not visible, light. (Source: UCLA)
PSCs aren't entirely new, but truly transparent ones are. Previous attempts to make PSCs that are partially or completely transparent to the naked eye have either resulted in devices that are transparent to visible light but not very efficient, or efficient devices that aren't really transparent. The researchers say that this is mostly because the devices were not fabricated with the best combination of polymeric PV materials and efficient transparent conductors. For example, opaque metal electrodes have typically been used.
The UCLA PSCs are lightweight, flexible, and have a maximum transparency of 66 percent at 550nm. They incorporate near-infrared (NIR) photoactive polymer and use a highly transparent silver nanowire-metal oxide composite conducting film as the top transparent electrode. The NIR light-sensitive photoactive polymer balances transparency at visible wavelengths by harvesting solar energy from NIR wavelengths while being less sensitive to visible photons.
The transparent conductor is a major breakthrough, the researchers say. It's made of a mixture of silver nanowire and titanium dioxide nanoparticles. This composite electrode makes it possible for the PSCs to be fabricated in high volume at low cost, via mild solution processes. The transparent PSCs have a power-conversion efficiency of 4 percent.
Other authors of the study are CNSI director Paul S. Weiss; CNSI postdoctoral researcher Yue Bing Zheng; materials science and engineering postdoctoral researcher Rui Zhu; doctoral candidates Chun-Chao Chen, Letian Dou, Choong-Heui Chung, Tze-Bin Song, and Steve Hawks; and Gang Li, former vice president of engineering for Solarmer Energy Inc. The study received funding supported from the Henry Samueli School of Engineering and Applied Science, the Office of Naval Research, and The Kavli Foundation.
I agree, Beth, the large buildings have the scale. A small savings per window would deliver significant power. In a dense area like Manhattan, there may be some limitations on direct sunlight, but around most of the country, these large buildings are pretty clear of obstruction.
Commercial buildings would be a great application and these mega buildings also have some sort of budget which would allow them to invest in the storage capabilities that are so critical to making this effective. Especially since many mega buildings in cities (I'm thinking NYC) have lots of self-induced shade due to their size and number--a factor that could limit the windows' ability to harvest energy even on sunny days.
Energy harvesting technologies are well-known to produce really tiny amounts of electrical current -- at the microamp- and even nanoamp-level in some cases. Any idea how much these films could produce, Ann?
I would guess the most efficient use of this technology would be on high-rise office buildings. The tall buildings have acres of windows, far more per square foot than a private residence.
I agree entirely. With a consumer grade cell at 15%, a 4% cell that will probably not be properly aligned is going to need to be fairly cheap. Don't get me wrong, I love solar, I even converted my lawn mower to solar. The idea of a window that still functions as a window while collecting solar energy is fantastic, but if each window only collects 1Wh for a sunny day, the window will need to be as cheap as glass.
I agree with you totally. This idea of adding solar cell polymer material to windows is the best one yet for generating electricity. With the amount of sunlight passing through windows daily, I would imagine sufficient amounts of electricity can be generated easily. The next item to include in the energy conversion process is an innovative way to store the energy for use on cloudy days.
This is a really cool development. The real key (costs aside) will be integration of "power windows" into a local smart grid. In this case local would mean within the confines of the building that the windows are installed in. What a great way to harvest power for low voltage lighting, though.
It's sources report the following efficiencies for conversion of sunlight into biomass (usable energy)
Plants 0.1% - 2 %
Crops 1% - 2%
Sugarcane 7% - 8%
At 4%, this device is on the high-side when compared to energy-harvesting bio-fuels. With even more development, this material could be quite a winner -- and we could continue to use our corn and soybeans to feed people and livestock rather than engines...
At 4% efficiency, and a practical application on the south side of office buildings, cost is going to be the deciding factor. Let's hope that taxpayers don't get stuck funding this as the total outpput could be rather restricted.
I wouldn't mind having those windows, either, even here in the woods. There are various types of films that can be added to windows that purport to do something similar. Here are some recent ones:
http://www.pcworld.com/article/241152/3m_film_turns_windows_into_transparent_solar_panels.html
http://cleantechnica.com/2012/07/06/39893/
http://www.newenergytechnologiesinc.com/technology/solarwindow
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Researchers at the Missouri University of Science & Technology have designed a new nanoscale material that can transmit light faster than the 186,000 miles per second it usually takes to travel through air.
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