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Miniaturized Energy on the Dot

April 6, 2012
By Beverly Schaeffer

Solar energy is now being taken to a whole new level-but it's a smaller level this time, not a bigger one. A solar cell no larger than the dot over the letter "i" is breaking records by setting new standards for efficiency. Particularly in hot, dry regions, this solar-provided power could be much less expensive, making solar energy more competitive with conventional energy sources. In this issue of SIGNAL Magazine, which features a focus area on energy technologies, Technology Editor George I. Seffers discusses the tiny tot of the solar industry in his article "Dot-Sized Solar Cell Supplies Substantial Power." Developed in part with $3 million in seed money from the U.S. Energy Department's National Renewable Energy Laboratory (NREL), the solar dot has earned its reputation as a powerhouse of concentrated photovoltaic (CPV) energy. First, the NREL verified late last year that the cell converts into electricity up to 41 percent of the sunlight reflected onto it-one of the highest conversion rates ever recorded. In late January, two organizations in Spain verified that a solar panel made up of these tiny cells broke world records in efficiency at 33.9 percent. Both the Instituto de Energía Solar at the Universidad Politécnica de Madrid and the Institute of Concentration Photovoltaic Systems, Puertollano, verified the panel's efficiency rate. With the previous world record at 32 percent, this means that the recent achievement also marks the first time solar technology converted more than one-third of the sun's energy into electricity. The typical conversion rate for existing technologies is about 10 to 15 percent, experts say. The cells are developed by Semprius Incorporated, and its relationship with the NREL began in 2010 when the company submitted a prototype module for development funds under the NREL's SunShot Incubator Program. According to Russ Kanjorski, Semprius vice president of business development, CPV technology is in its infancy with potential advances still to be made:

There have been some large-scale installations-in the neighborhood of 30 megawatts. And some folks have done single-digit megawatt installation, but this technology is really just starting ... It's in such early stages that there are many opportunities for additional improvements and efficiency and lowering costs and doing things smarter.

Semprius uses micro-transfer printing, which includes removing and transferring the top layer of a gallium-arsenide source wafer to an inexpensive mounting substrate so that thousands of cells are processed in parallel. This allows the expensive gallium-arsenide source substrate to be used multiple times. Kanjorski also makes it clear that the solar dot technology is intended to provide more efficient electrical utilities and not for other uses, such as solar-powered automobiles:

We're not focused on anything with a moving application or even on rooftops. Our focus is on ground-mounted-as opposed to roof-mounted-solar, especially in the larger-scale applications, utility scale.

The company has partnered with Siemens Industry Incorporated, Atlanta, to co-develop demonstration systems based on Semprius' solar module arrays and Siemens' automation and control components. The systems are slated for installation at numerous test sites worldwide, including major utilities, commercial sites, international test locations and government facilities. The solar dot is an amazing technology, but what other uses could it be applied toward? Why not develop solar dot technology for ground vehicles and other applications? Share your impressions and ideas here.

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