14 July 2009

Solar power system gets redesign

Four newly designed solar power collection dishes have a refined design that will be ready for commercial-scale deployments starting next year.

“The four new dishes are the next-generation model of the original SunCatcher system,” said Chuck Andraka, the lead project engineer at Sandia National Laboratories National Solar Thermal Test Facility (NSTTF). “Six first-generation SunCatchers built over the past several years at the NSTTF have been producing up to 150KW [kilowatts] of grid-ready electrical power during the day. Every part of the new system has been upgraded to allow for a high rate of production and cost reduction.”

Rendering of SunCatchers

Sandia’s concentrating solar-thermal power (CSP) team has been working closely with Stirling Energy Systems (SES) over the past five years to improve the system design and operation.

The modular CSP SunCatcher uses precision mirrors attached to a parabolic dish to focus the sun’s rays onto a receiver, which transmits the heat to a Stirling engine. The engine is a sealed system filled with hydrogen. As the gas heats and cools, its pressure rises and falls. The change in pressure drives the piston inside the engine, producing mechanical power, which in turn drives a generator and makes electricity.

The new SunCatcher is about 5,000 pounds lighter than the original, is round instead of rectangular to allow for more efficient use of steel, has improved optics, and consists of 60% fewer engine parts. The revised design also has fewer mirrors, 40 instead of 80. The reflective mirrors form into a parabolic shape using stamped sheet metal similar to the hood of a car. The mirrors come together using techniques borrowed from the automobile manufacturing industry. The improvements will result in high-volume production, cost reductions, and easier maintenance.

Among some of the new design concepts were the development of a tool to determine how well the mirrors work in less than 10 seconds, something that took the earlier design one hour.

“The new design of the SunCatcher represents more than a decade of innovative engineering and validation testing, making it ready for commercialization,” said Steve Cowman, Stirling Energy Systems chief executive. “By utilizing the automotive supply chain to manufacture the SunCatcher, we’re leveraging the talents of an industry that has refined high-volume production through an assembly line process. More than 90% of the SunCatcher components will be manufactured in North America.”

In addition to improved manufacturability and easy maintenance, the new SunCatcher minimizes cost and land use and has numerous environmental advantages, Andraka said.

“They have the lowest water use of any thermal electric generating technology, require minimal grading and trenching, require no excavation for foundations, and will not produce greenhouse gas emissions while converting sunlight into electricity,” he said.

Tessera Solar, the developer and operator of large-scale solar projects using the SunCatcher technology and sister company of SES, is building a 60-unit plant generating 1.5 MW (megawatts) by the end of the year either in Arizona or California. One megawatt powers about 800 homes. The proprietary solar dish technology will then deploy to develop two of the world’s largest solar generating plants in Southern California with San Diego Gas & Electric in the Imperial Valley and Southern California Edison in the Mojave Desert. The projects should produce 1,000 MW by the end of 2012.

Last year, one of the original SunCatchers set a new solar-to-grid system conversion efficiency record by achieving a 31.25% net efficiency rate, toppling the old 1984 record of 29.4%.

For related information, go to www.isa.org/manufacturing_automation.