| Saguaro Solar
Station Commemorated on Earth Day
APS, Solargenix Inc. and Schott North America, Inc. commemorated on
April 22 in Red Rock, Ariz., the completion of the first solar thermal
parabolic trough power plant. The Saguaro Solar Generating Station is
the nation's first solar thermal parabolic trough power plant built
specifically to produce electricity since 1988. The Saguaro Station power plant was built by Solargenix, a solar energy development company based in Raleigh, N.C., and a subsidiary of ACCIONA Energy of Spain, a company devoted to renewables. The plant will be operated by APS, Arizona's largest and longest-serving electric utility, based in Phoenix, Ariz. The 1 MW Saguaro Solar Generating Station has been generating electricity since December 2005, using several hundred PTR 70 solar receivers produced by SCHOTT, an international leader in innovative solar solutions. “Solar thermal parabolic trough power plants have the potential to be an important source of renewable energy as the world seeks to reduce its dependence on fossil fuels,” said Dr. Udo Ungeheuer, chairman, SCHOTT Management Board. “The Saguaro Power plant is a significant step forward for Arizona as it seeks to reach its goal of generating 15 percent of its electricity from renewable resources within the next 20 years.” The Saguaro Station power plant uses 100,000 square feet of parabolic mirrors to concentrate solar radiation onto its PTR 70 solar receivers. This solar radiation increases the temperature of the thermo-oil Heat Transfer Fluid (HTF) flowing through the receivers to 550° F. This heated fluid is then used to turn water into steam, which drives a turbine and generates electricity. The Saguaro Station power plant uses an organic rankin cycle system for its turbine/generator, which enables the plant to produce more power at lower temperatures. In addition, the organic rankin turbine can be operated automatically, reducing costs. The Saguaro Station power plant is expected to produce 2000 MWh of electricity annually, enough electricity to meet the energy demands of about 200 households. The use of solar power to produce electricity at the plant, rather than fossil fuels, is equivalent to preventing the emission of millions of pounds of carbon dioxide into the atmosphere each year. The SCHOTT PTR 70 receivers used at Saguaro Station incorporate several features that make solar thermal power more dependable and affordable, including: New anti-reflective glass coatings: Previous glass coatings failed to adhere to solar receivers’ borosilicate glass outer envelope tubes over time. SCHOTT has developed a new anti-reflective glass coating for its receivers that resists abrasion for years, while still allowing more than 96 percent of solar radiation to penetrate the receiver and heat the heat transfer fluid within. --New absorptive steel coatings: In order to achieve peak efficiency, the steel absorber tube located inside the outer glass envelope tube needs to absorb as much solar radiation as possible while releasing as little heat as possible. SCHOTT’s new absorptive steel coating improves radiation absorption rates to 95 percent, while helping ensure that no more than 14 percent of the heat from the steel tube is released. --Improved glass-to-metal seals: In other solar thermal receivers, differences in the thermal expansion of the inner steel tube and the outer glass envelope tube resulted in tube failure when there were severe shifts in temperature. The new PTR 70 receiver uses a new borosilicate glass with the same thermal expansion coefficient as steel. The result is a receiver that can handle the changes in temperature that occur as cool Arizona desert nights quickly become hot desert days. This improvement was designed to reduce both maintenance time and the need for replacement parts.
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