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FEA Finds a Place in the Sun PUBLIC ACCESS

Finite-Element Analysis is Helping Engineers Optimize Emerging Solar-Energy Technologies, so they can Meet Market Demand for Lower Installation Costs and Increased Production.

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Executive Editor

Mechanical Engineering 120(08), 81-82 (Aug 01, 1998) (2 pages) doi:10.1115/1.1998-AUG-10

This article reviews that finite-element analysis (FEA) is helping engineers optimize emerging solar-energy technologies, so they can meet market demand for lower installation costs and increased production. As producers of electricity investigate ways to meet new and existing demand for power without increasing pollution, more and more utilities—especially those in areas of high solar insolation—are looking more seriously at renewable energy sources, such as solar power. Engineers at Science Applications International Corp.(SAIC), headquartered in San Diego, have developed a parabolic dish system for distributed-receiver applications and central-receiver (power tower) systems, which use a large field of mirrored heliostats. The parabolic dish system is projected to be a promising option worldwide, especially in remote areas that are currently without electricity. The testing at Solar Two will help engineers gain insight into the heliostat’s design, fabrication, installation, performance, and reliability. According to SAIC, this is a key step toward the first 50-megawatt electric power tower plant to be located in the national solar enterprise zone in the southwest desert.

Although Power Generation is by far the world's largest business, nearly one-third of the Earth's population remains without access to electricity. As producers of electricity investigate ways to meet new and existing demand for power without increasing pollution, more and more utilities-especially those in areas of high solar insolation-are looking more seriously at renewable energy sources, such as solar power. Emerging technologies in this area, such as conm1ercial heliostats for solar-central-receiver applications and parabolic-dish concentrators for distributed-receiver applications, show promise of being able to compete on a cost basis with conventional power-generation sources, while helping to reduce current pollution levels.

With funding from the U.S. Department of Energy in Washington, D.C., and private investors, among others, engineers at Science Applications International Corp. (SAIC), headquartered in San Diego, have developed a parabolic dish system for distributed- receiver applications and central-receiver (power tower) systems, which use a large field of mirrored heliostats. The parabolic dish system is projected to be a promising option worldwide, especially in remote areas that are currently without electricity.

Engineers at SAIC use Algor finite-element-analysis software to analyze heliostat structures for wind, gravity loads, and natural frequencies.

Grahic Jump LocationEngineers at SAIC use Algor finite-element-analysis software to analyze heliostat structures for wind, gravity loads, and natural frequencies.

Designed and constructed at SAlC's test site in Golden, Colo., the dish concentrator employs paraboli c-shaped mirrors of thin stainless-steel membrane stretched over a steel ring. The mirrors focus the sun's rays onto a thermal receiver that extends from the center of the structure. The solar energy runs a Stirling heat engine, manufactured by Stirling Thermal Motors, Inc., which operates at a solar-to-electric conversion efficiency of over 24 percent. By optimizing the cost per kilowatt-hour, SAIC projects that this product will be viable for use by private and government electric utilities. The optimized design is being installed at five sites throughout the southwestern United States.

Interactive Analysis

To ensure that a promising technology meets actual market needs, SAIC engineers are working to reduce material usage, decrease installation costs, and improve production of the dish concentrator system. This requires the ability to produce many iterations of a design quickly and easily, so that design trade-offs can be managed effectively and various aspects of the designs can be optimized. SAIC engineers are using Algor finite- element-analysis (FEA) software, from Algor Inc. in Pittsburgh, to evaluate design iterations as soon as they're produced.

For example, with each design modification , wind, gravity loads, and natural frequencies were analyzed using the FEA software. "Algor is very interactive," said Jeffrey Sandubrae, P.E., a senior engineer with SAle. "I can generate models easily, run a series of analyses, and modify the models based on the results."

Unlike dish systems, which may be used individually, central-receiver systems employ heliostats in larger installations. The heliostats typically are focused around a central receiver that collects the sunlight and transfers the sun's heat to a steam turbine for electricity generation. Each heliostat uses 22 flat mirrors per structure to focus sunlight onto the receiver. The heliostat structure was analyzed for wind, gravity loads, and natural frequencies. "The software has become so much more graphical and easy to use over the years," Sandubrae said. "Recently, I've been using the animation capability to create AVI files of mode shapes and deformed shapes. It's very helpful to see these types of movement in action."

This parabolic dish system generates enough solar energy to achieve a solar-to-electric conversion efficiency exceeding 24 percent, more than any other type of large solar-power system.

Grahic Jump LocationThis parabolic dish system generates enough solar energy to achieve a solar-to-electric conversion efficiency exceeding 24 percent, more than any other type of large solar-power system.

A prototype heliostat is currently being tested at SAlC's Golden, Colo., site. Additional heliostat installations are planned at Sandia National Laboratories in Albuquerque, N.M., for optical testing, and at Solar Two, a pilot power tower plant at Dagget, Calif., for extended field tests.

The testing at Solar Two will help engineers gain insight into the heliostat's design, fabrication, installation, performance, and reliability. According to SAIC, this is a key step toward the first 50- megawatt electric power tower plant to be located in the national solar enterprise zone in the southwest desert.

Copyright © 1998 by ASME
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