Auto suppliers catch the sun's energy

  • 10-Dec-2009 11:52 EST
Stirling Energy Systems SunCatcher.jpg
The current SunCatcher "is easy to manufacture and easy to assemble, and it is serviceable to the requirements of our project sites," said SES' Jeffrey Collins.

Companies long associated with the automotive industry have a vital role in capturing the sun's reflective energy and converting the heat into renewable power.

Beginning in 2010, several hundred Stirling Energy Systems Inc. (SES) SunCatcher systems will form the nucleus of providing utility-scale power in California, Arizona, and Texas. When all 65,140 solar dish systems from those initial projects go online, more than 1628.5 MW of electricity will be produced.

But getting concentrated solar power technology to the point of commercialization was an evolving and lengthy process of re-engineering and redesigning the system, including the components in the power conversion unit (PCU) that hangs from a boom.

In short, SES needed its next-generation SunCatcher system to be as easy to service and mass-produce as a vehicle. "We were at a crossroads as to whether we were going to vertically integrate or whether we were going to leverage the expertise of supplier partners. We chose this model: outsourced engineering, outsourced manufacturing, and outsourced supply chain," said Jeffrey Collins, Vice President of Global Supply Chain for SES.

Tower Automotive, a global supplier of automotive metal structural components and assemblies, is contracted for the production and assembly of the SunCatcher's mirror facets that create the highly reflective surface on the 38-ft (11.6-m) parabolic solar dish. Affixed to structural steel supports, the 40 concave-shaped mirror facets—each about 7 ft (2.1 m) in length—focus the sun's energy onto an 8-in (203-mm) aperture at the PCU's entrance.

The 600-plus parts within the 1754-lb (795.6-kg) PCU are sourced to Linamar Corp. of Guelph, Ontario, Canada. Livonia, MI-based McLaren Performance Technologies, a division of Linamar, handles prototyping, testing, and validation of the PCU. It assisted with the design and development of the PCU's closed-cycle, four-cylinder Stirling engine.

"The basic principle of the engine is it takes concentrated heat—in this case the reflection of the sun's energy from the dish—and focuses it on an array of tubes, each containing hydrogen gas. The heat causes the gas to expand, which drives the engine's pistons to turn the two crankshafts, which are indirectly connected to a generator. In summary, the engine efficiently converts heat to electricity," said Philip Guys, Vice President of Engineering for Linamar and President of McLaren Performance Technologies, whose automotive history includes Buick turbocharged V6 engines for various Motorsports series.

Compared to proof-of-concept versions of the SunCatcher, the commercialized system is modular, scalable, and has fewer components, said Steve Rolfe, Senior Manager of Engine Engineering for McLaren Performance Technologies. For instance, the current PCU has four coolers and four regenerators vs. the previous eight coolers and eight regenerators. "Even though the surface area is the same, the current PCU has much more efficient packaging—including a more direct route for the hydrogen gas to follow. That allowed us to reduce the number of coolers and regenerators. We also redesigned the PCU with a single radiator vs. the previous three radiators."

The role of the regenerators and radiator is crucial to the SunCatcher's task of converting the sun's energy to utility-scale electricity. As hot hydrogen gas passes through the SunCatcher's regenerators, thermal energy is stored until the hydrogen gas returns during the transfer cycle; the radiator system cools the hydrogen gas as well as the square arrangement of cylinders within the cast iron block, according to Rolfe. Unlike many other solar electricity-generating systems, the SunCatcher conversion process does not consume water.

SunCatcher's concentrator dish is computer-programmed to automatically track, collect, and focus the sun's energy into the PCU's Stirling engine. At full production, 100 PCUs will be assembled daily, with the engine assembly coming from one Linamar plant and the cylinder block, piston rods, crankshafts, connecting rods, and other engine components coming from five Linamar plants. Final assembly will occur at a Linamar plant in the southwestern U.S.

"With an emphasis on design for manufacturability, we made changes from the practices used with the original PCU design that goes back 25 years," said Rolfe. "The mass-produced PCU also will benefit from the advancements in sealing technology, as the number of seals dropped approximately 30% compared to the proof-of-concept PCU."

The dish system—comprising the pedestal, the facet support structure, as well as the boom and castings that create the mounting mechanism atop the pedestal—had not been sourced as of press time. "We're evaluating proposals, but the contract likely will be awarded to a Tier 1 automotive supplier," said Collins.

The azimuth and elevation drives contract is likely to be sourced to a producer of heavy equipment. A portion of the electrical and electronic controls work for the demonstration unit was sourced to Siemens, but the electrical and electronic controls for the production SunCatcher had not been sourced as of press time, according to Collins.   

In September, groundbreaking occurred for the first 25-kW SunCatcher on a 15-acre (6-ha) site in Arizona. Owned and operated by Tessera Solar, the sister company of SES, the 60 SunCatchers in Maricopa County are slated to deliver power to the grid in January.

In late 2010, three other projects are slated to break ground. Those projects eventually will involve 30,000 SunCatchers in Imperial County, CA (supplying grid power to San Diego Gas and Electric); 34,000 solar dish systems in San Bernardino County, CA (supplying grid power to Southern California Edison); and 1080 SunCatchers in western Texas (supplying grid power to CPS Energy).

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