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First Solar Thermal Parabolic Trough Power Plant Dedicated On Earth Day

APS, Solargenix Inc and Schott North America, Inc will commemorate the completion of the first solar thermal parabolic trough power plant to be built in Arizona on Earth Day, April 22, from 10 to 2 pm in Red Rock, Arizona. The plant is located about 30 miles north of Tucson, just off Interstate 10.

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 world leading 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 of the 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.”

How Parabolic Trough Power Plants Work

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 [Figure 1]. This heated fluid is then used to turn water into steam, which drives a turbine and generates electricity [Figure 2].

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.

Southwestern States Set High Renewable Energy Standards

In February, the Arizona Corporation Commission mandated that electric utilities in Arizona generate 15 percent of their electricity from renewable resources by 2025. With this measure Arizona joins other states located in the southwestern United States which have set ambitious renewable energy mandates including:
• California (20 percent by 2010)
• Nevada (20 percent by 2015)
• New Mexico (10 percent by 2011)

Since they require direct sunlight, large-scale solar thermal power plants are best suited for sunbelt areas of the world, like the southwestern United States.

When compared to other forms of renewable energy, solar thermal power offers several advantages, including:
• Reliability: The 354 MW California SEGS solar thermal parabolic trough power plants in California\'s Mojave Desert have produced billions of kilowatt hours of electricity for the past two decades
• Availability: Unlike wind power, solar thermal power can deliver a steady supply of electricity during daylight hours, when utilities usually see peak demand for electricity.
• Low Cost: Recent technological innovations have made solar power more efficient. In fact, a report from the NREL predicts that solar thermal power might be cost-competitive with conventional fossil fuel electricity generation as soon as 2020.

Technological Advancements Lower Costs, Improve Efficiency

SCHOTT’s new PTR 70 solar receivers are one of the technological innovations that have helped lower the cost and improve the reliability of solar thermal parabolic trough power plants.

“For many years, renewable energy has been seen as too unreliable and too expensive to compete with fossil fuels,” said Steve Russo of SCHOTT’s North American solar thermal business. “Thanks to innovations such as the PTR 70, solar thermal power and other forms of renewable energy are now a real alternative to traditional sources of energy.”

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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