Public Power - July/August 2008 - (Page 22)

Solar Energy Rising At 64-MW, Nevada Solar One is the largest concentrating solar power project in the country and the third largest in the world. Photo by Steve Marcus, Associated Press Solid state mono or multi-crystalline silicon (Si) wafers (or ribbon) constitute first generation photovoltaic technology and are hundreds of microns thick. Crystalline silicon cells have been the workhorse of the photovoltaic industry for decades. Cells are assembled into arrays called panels or modules. They generate DC power, requiring inverters that add cost and create energy losses between 10 and 20 percent. Second generation “thin-film” photovoltaic relies on silicon alternatives such as amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium-gallium/diselenide (CIGS). While not as efficient, these materials weigh less, cost less to manufacture and require far less material. Cells made from these materials only need to be one or two microns thick. Most important, second generation photovoltaic is produced on large, flexible sheets, as the name “film” suggests. It can be used with a wide range of substrates, such as plastic and glass, allowing its integration with building materials. This has enabled cost reductions that are driving the fast-growing building-integrated photovoltaic (BIPV) market, in part because they reduce or eliminate the need for mounting and other photovoltaic system components. Thin-film photovoltaic, especially the aSi and CdTe varieties, have been 22 JULY-AUGUST 2008 encroaching on first generation photovoltaic market share in the United States for about 10 years. According to EIA, thinfilm’s market share increased steadily from 12 percent in 2004 to 24 percent in 2005 and 30 percent in 2006. NanoMarkets expects thin film to have 50 percent of the market by 2015. Some researchers, includ- multiple exciton generation cells, which leverage impact ionization—a process that maximizes the effects of high energy protons, according to EPRI. Other third generation technologies are optical frequency shifting, which transforms the solar spectrum to maintain its power density within a narrow range of photon energies; and hot carrier cells that reduce heat losses in single-junction cells. Such concepts may lead to higher efficiency organic photovoltaic solar cells enabled by recent refinements in composition, device engineering and cell physics or materials such as carbon nanotubes—strong, microscopic cylindrical “towers,” or rods, of carbon that can be grown with coatings of semiconductor material over silicon wafers. Organic photovoltaic modules, such as dye-sensitized cells, can use diffused light, are flexible, transparent and lightweight, but are very inefficient and susceptible to damage from oxygen and water vapor. Nanotechnology researchers are working to develop the ability to print or even paint solar cells onto a range of different surfaces. Success here would enable an array of applications such as wearable electronics, “smart windows” and solar-charged cell phones. One company, Nanosolar, said Nanotechnology researchers are working to develop the ability to print or even paint solar cells onto a range of different surfaces. ing National Renewable Energy Laboratory’s von Roedern, believe this growth will be enhanced due to limitations in the supply of high grade silicon used in first generation devices, in addition to inherent cost advantages of efficient thin-film photovoltaic technologies over wafer or ribbon silicon based technologies. A large and exotic array of cutting-edge concepts makes up third generation photovoltaic technologies, none of which have gone commercial. They rely mainly on organic matter and nanotechnologies. Third generation concepts include it is already able to “simply roll-print thinfilm solar cells.” Researchers track ratings of photovoltaic solar conversion efficiency—the amount of sunlight that gets converted to electricity— for the myriad combinations of materials and designs that have been developed. Each technology has a different theoretical upper limit due to physical constraints. Industry and government research labs regularly announce new records. To track the progress, National Renewable Energy Laboratory divides photovoltaic cells into four categories—multi-junction concentraPUBLIC POWER

Table of Contents Feed for the Digital Edition of Public Power - July/August 2008

Public Power- July/August 2008 Contents Perspective 10 Questions Solar Energy Rising Sacramento's Solar Shares Gainesville Crowns a Conservation Idol By the Numbers Curbing Costs of Outages Reliability Green Energy Hometown Connections Customer Service Parting Shot

Public Power - July/August 2008

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