Next generation of solar dishes use less steel

www.sfgate.com
July 18, 2009

Sandia National Laboratories scientist Chuck Andraka is excited about what's missing from a new generation of solar dishes that will be in the field by next year. There's far less steel — about 2 tons — in the structure that supports the SunCatcher, developed for Scottsdale, Ariz.-based Stirling Energy Systems, or SES. Overall, the design is 5,000 pounds lighter than its prototype. "You've got to get the cost down because there's so little margin," said Andraka, lead engineer on the project. "Small changes.., impact profitability."

Sandia morphed the SunCatcher's original rectangular design into a radial structure that looks like a 37 1/2-foot diameter satellite dish with mirrors and allows "the same structural stiffness with far less steel," he said. The lab's work on the SunCatcher was done with manufacturing in mind. "The idea wasn't to enhance performance. It was to make it more manufacturable and get the cost down," Andraka said.

And that's the point. The project is part of a larger effort to make solar energy more affordable for utilities and other potential customers. "This is an example of the momentum we're seeing in industry for incremental improvements to bring costs down across the entire supply chain," said Monique Hanis, spokeswoman for the 35-year-old Washington, D.C.-based Solar Energy Industries Association.

She said the industry sees "huge opportunities on the utility-scale front" with Monday's announcement by Interior Secretary Ken Salazar that his agency will designate 670,000 acres of federal land in Nevada, Arizona, California, Colorado, New Mexico and Utah as study areas for utility-scale solar projects.

The newest SunCatcher version has fewer pieces, so there's less inventory to keep and fewer pieces to assemble. The design retains the functionality of the previous one but is far easier to repair. "Something that was taking our technicians a week to service, they should be able to service in two hours now," Andraka said. SunCatcher's developers also expect it to benefit suppliers in the hard-hit automotive industry.

"Parts of it are steel and mirrors and glass, all the things they use to make vehicles up in the Detroit area," said Janette Coates, spokeswoman for Tessera Solar, SES's Houston-based solar project development arm. The design uses radiators for cooling. It's a closed system like those on automobiles, reducing evaporation, which Andraka said provides a huge advantage in a desert environment.

Sandia began working with SES on the project in 2002, and the next year, SES brought in a dish purchased from another manufacturer. In 2005, Sandia installed an SES-built system. That prototype proved the concept works, which led to the current design. "It really was a crash course on redesign," Andraka said.

SunCatchers, each producing 25 kWs of electricity, will be placed in arrays covering many square miles to generate power for utilities. "It has a huge potential to deliver real power to our country," said Andraka, who has worked on the project for much of the decade. This is how Sandia explains the SunCatcher's workings: The modular design uses mirrors attached to a parabolic dish that focuses the sun's rays onto a receiver, which transmits heat to a Stirling engine, a sealed system filled with hydrogen.

As the gas heats and cools, its pressure rises and falls, and the change in pressure drives a piston inside the engine. That produces mechanical power, which drives a generator and makes electricity. The structure rotates to follow the sun. The solar collection dishes don't resemble the trough or solar panel arrays most people are accustomed to seeing.

"That's one of the confusions we have often. They think photovoltaic and rooftop," Andraka said. "These are not rooftop. These are utility scale, square miles (of dishes) in a location." In a particularly bright area, a utility could remove mirrors that gather sunlight; in a cloudier coastal area, it could add some, Andraka said.

Tessera Solar plans a 60-unit generation plant in Arizona or California. The plant, expected to go into operation by January, would generate 1.5 MWs. The company also plans to use the technology in two large plants to go into operation by the end of 2012 in Southern California. Together, they would generate enough electricity for nearly 1.2 million homes, Coates said.

One under development with San Diego Gas & Electric in the Imperial Valley, would generate 750 MWs. The second, east of Barstow with Southern California Edison, would generate 850 MWs. Tessera also is developing a 27-MW West Texas project with CPS Energy. That project is expected to begin operating by the end of next year.

Andraka said projects move faster in the investor-driven industry sector. "The bulk of the money is coming from investors. It's not coming from the government," he said. "That's a huge change in pace.., because investors want results and they want them now."