When many of us think about solar energy we imagine large, rigid panels covering the roof of a building. Solar energy technologies have come a long way from those days, and in addition to seeing panels covering rooftops, you're also likely to see solar energy technology popping up in unexpected places, including backpacks. Converting sunlight into energy through photovoltaic devices is one of the greenest energy options (despite the manufacturing pollution). When in use, these cells sit in the sun, absorb rays and release nothing more than electrons. Capture these and you can generate electricity.
What if you could capture and use the sun's energy with an accessory you likely wear every day: your sunglasses. Designers Hyun-Joong Kim and Kwang-Seok Jeong have created some conceptual shades that will not only protect your eyes from the sun's dangerous UV rays but also convert those rays into electrical energy -- energy that could be used to power a small device such as an iPod, PSP or mobile phone whether you're on the beach or on the go.
These sunglasses, called Self-Energy Converting Sunglasses or SIG for short, have special lenses that are made with dye-sensitized solar cells (DSC). The lenses convert solar energy into electricity that you can tap into by plugging a device into the power jack at the back of the frame. While it's not a lot of power, it should be enough to juice a battery for a few extra minutes or keep the tunes playing while you bask on the beach. While there's no retail date or price on these sunglasses yet, the designers had cost in mind when they came up with the idea. The lenses use cheap, organic dye to provide this clean energy. How can a cheap organic dye translate into clean battery power? It's all in the DSC technology.
Dye-sensitized Solar Cells
Dye-sensitized solar cell (DSC) technology, also called Grätzel cells, were first introduced in 1991 by Michael Grätzel, a chemist at the Swiss Federal Institute of Technology, Lausanne, and his colleagues.
There have been a few iterations of DSC technology, and the latest type of solar cell belongs to a new age of thin-film photovoltaic devices. They are engineered in layers: a photosensitive layer made of ultrathin, nano-sized semiconductor crystals over a thin layer of titanium dioxide. When photons (from sunlight) hit the photosensitive layer, the freed electrons accumulate on the layer of titanium dioxide and create an electrical current. Previously, a liquid electrolyte was needed to carry the electrons from one layer to another but in the newest generation of Grätzel cells, a dye made of amorphous organic material is used to coat the titanium dioxide -- the dye absorbs light and attracts excited electrons, which generates a charge.
The results are cells that can be used to create low-cost, lightweight, transparent and flexible sheets or dye that could be used to coat glass, such as the windows of your house to supply energy to your home. Or it could be used to coat the lenses of sunglasses and provide power to small-device batteries.
DSC technology is highly efficient compared to other forms of solar cells, producing efficiencies greater than 11 percent -- meaning that 11 percent of the captured solar energy is converted to electrical energy -- rather than 4 to 5 percent [source: ScienceDaily]. But in small applications, such as in sunglasses, there could be one potential problem: Solar cells need to be facing the sun to absorb rays. How often do you stare into the sun?
Advances in Solar Cells
Sun exposure becomes less of an issue when you think about applying thin-film photovoltaic devices to places such as windows, skylights and even a building façade to make its exterior photovoltaicly active.
While conventional solar panels, made from silicon cells, continue to have an advantage over this new solar technology, they remain inflexible, expensive and compared to the newest innovations, no longer the most efficient option. Dye-sensitized solar cells (DSCs) have a few other tricks up their sleeve. They are able to work as efficiently at 149 degrees F (65 degrees C) as at 77 degrees F (25 degrees C), whereas silicon cells lose 20 percent of their energy efficiency at extreme temperatures.
And because of the wafer-thin and flexible properties, DSC technology can be applied in ways never considered for conventional cells. Militaries, for instance, have become interested in Grätzel cells. New tents and fabrics are able to provide up to 1 kilowatt of energy (enough to power a few lights and a laptop) [source: Tent Manufacturers Marketplace]. And on a larger scale, flexible solar panels used to cover tents power sophisticated equipment. Additionally, Grätzel cells could be engineered into wearable photovoltaic cells. Lightweight wearable solar panels could power and recharge all electrical devices soldiers or Marines carry, eliminating the need for extra battery packs or bagfuls of batteries in the field.
While DSC technology has new groundbreaking applications, research into other areas of solar energy shows promise in plastic solar cells -- an idea where layers of titanium oxide are chemically modified -- that could have energy efficiency levels greater than those seen in Grätzel cells. Maybe one day not only will the lenses be photovoltaic, but the entire pair of sunglasses will be an energy source.
How Solar-powered Sunglasses Work: Author’s Note
It's always a bit nerve-wracking to write about a product when it's still in concept. Will there be information available about how the product works? Is there a prototype? Sometimes you're working with neither, but in the case of the solar-powered sunglasses I was able to piece together how these sunglasses work -- it's all about photovoltaic cells. Note: I have to confess the entire time I was writing this piece I kept thinking how these oversized white frames reminded me of Willy Wonka's sunglasses in Tim Burton's version of “Charlie and the Chocolate Factory.”
- Bullis, Kevin. "Solar Cells for Cheap." Technology Review. MIT. 2006. http://www.technologyreview.com/read_article.aspx?id=17490&ch=biztech&sc=&pg=1
- Fountain, Henry. "Photovoltaic Cells Are Still Very Green, Comparative Test Shows." The New York Times. 2008. http://www.nytimes.com/2008/02/26/science/26obsola.html?_r=1
- Graham-Rowe, Duncan. "Hello, sunshine." New Scientist. 1998. http://www.newscientist.com/article/mg16021551.600-hello-sunshine.html
- McGrath, Matt. "Solar dyes give a guiding light." BBC. 2008. http://news.bbc.co.uk/2/hi/technology/7501476.stm
- Simonite, Tom. "Carbon electrodes could slash cost of solar panels." New Scientist. 2007. http://www.newscientist.com/article/dn13103
- Smith, Sherri L. "Solar-Powered Sunglasses To Power Your Gadgets." Fast Company. 2008. http://www.fastcompany.com/blog/sherri-l-smith/high-wire/let-sun
- "Solar Energy: Charged For The Future." ScienceDaily. 2006. http://www.sciencedaily.com/releases/2006/09/060911102937.htm
- "Solar Photovoltaic Cell/Module Manufacturing Activities." Energy Information Administration. U.S. Department of Energy. 2008. http://www.eia.doe.gov/cneaf/solar.renewables/page/solarphotv/solarpv.html
- "Solar Powered Solar Panel Sun Glasses." Yanko Design. http://www.yankodesign.com/2008/12/17/solar-powered-solar-panel-sun-glasses/
- Tent Manufacturers Marketplace. http://www.tentmanufacturers.net/army-tents.html
- "Ultrathin, Dye-sensitized Solar Cells Called Most Efficient To Date." ScienceDaily. 2006. http://www.sciencedaily.com/releases/2006/09/060918201621.htm
Solar-powered Sunglasses: Cheat Sheet
Stuff You Need to Know:
- These Self-Energy Converting Sunglasses (SIG) are able to absorb solar energy through special lenses coated with dye-sensitizing solar cells (DSC). In addition to being used as a glass-coating dye, these cells can also be turned into low-cost, lightweight, transparent and flexible sheets.
- Solar cells are engineered in two layers: a photosensitive layer made of ultrathin, nano-sized semiconductor crystals over a thin layer of titanium dioxide. When photons from the sun's rays are absorbed by the photosensitive layer, electrons accumulate on the titanium dioxide, creating an electrical current.
- When solar cells absorb the sun's rays and convert sunlight into electrical energy, it's called photovoltaics. What's released? Nothing more than electrons.
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