Solar Cells Info

Sean Snyder, Associate Editor — Design News, October 30, 2007
Source: Design News
http://www.designnews.com/article/CA6495765.html

As the cost comes down and the technology becomes more efficient, solar voltaic cells are being used for a number of new applications. Once an exotic technology, solar voltaic cells are now widespread throughout cities and rural environments, independent from the grid, or even adding power back to it. Energy density, efficiency and style are major concerns for solar voltaic cell applications, especially since market demand depends on practicality and aesthetics.

For compact applications, high energy density is crucial. “If you do a roof-top application where you are powering a house, you have the entire roof as a support,” says James Bears, director of research, development and engineering for Solar Outdoor Lighting Inc. (SOL) based out of Palm City, Florida. “You may then go to thin film more readily than if you are on a street light where you won’t want to block too much of the sky.”

SOL designs lights for transit and municipal applications, particularly in rural or developing areas that may not have access to a power grid or in instances where trenching costs are prohibitive for a connection to the grid.

“You want a fairly efficient panel for a street light to keep the size of the panel down, and those tend to be the polysilicon rather than the thin film, which are less efficient,” says Bears. “The thin film tends to be thinner, and one of the implications of that is the various wavelengths tend to travel through without being absorbed completely.”

Efficiency is always a concern when it comes to solar cells and energy collection. “The way I see it going is solar panels will use more quantum mechanical and nanotechnical innovations, thereby becoming more and more efficient, some approaching 50- and 60-percent efficiency as the panels use more of the different wavelengths of light, using quantum wells and that sort of thing,” says Bears.

Another company that is addressing the availability of solar voltaic cells and their ability to substitute grid-connected power supplies is Voltaic Systems, based in New York. Voltaic Systems has developed backpacks and bags with integrated solar panels used to charge personal electronic devices.

The bags use a monocrystalline cell to charge a lithium-ion battery, which then distributes the charge to an iPod or cell phone and (coming soon) to a laptop. A single cell is approximately 184 mm by 88 mm, has a peak voltage of 10.2V, a peak current of 133 mA and a peak watt rating of 1.36W. According to the website, the average time to charge a cell phone in direct sunlight is 4-6 hours, and to completely charge the battery would take 8-10 hours.

Solar trees, sculptural and functional representations of trees that use solar panels in place of leaves to gather the sun’s radiation, serve as another artistic and functional solar application. SMA International, a company based in Germany, suggests these solar trees be placed in the empty corners of parking lots. According to its website, “with an average power of 400 Wp (watt peak), the individual units are admittedly not particularly powerful, but there are many free corners, which add up to a lot of electricity.”

Various devices and systems are being developed around solar voltaic energy. However, according to Bears, “the technology is moving but the promises are far more readily available than some of these products.”