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  • From Autos to Solar

Photonics Spectra
Feb 2009
Anne L. Fischer, Senior Editor,

There is nothing like making the best of a bad situation. Solar company Infinia Corp. of Kennewick, Wash., may be able to take advantage of the downward spiral of the auto industry. It makes a unique solar dish system that can be mass-produced by Tier 1 and Tier 2 auto suppliers right on the auto assembly line. (Tier 1 suppliers make products that are sold to auto manufacturers, such as General Motors Corp., while a Tier 2 supplier would sell to the Tier 1 supplier.)

In the Duke report mentioned in the previous article ("Greening the Job Market") it is estimated that idle auto production capacity can manufacture 40 million solar dish systems in a year, amounting to 120,000 MW of solar capacity and approximately a half-million manufacturing jobs.

Infinia’s predecessor, Stirling Technology Co., was established in 1985 with a focus on developing zero-maintenance, long-lived power generation and thermal energy conversion systems using its piston-free engine. The engine resulted from a program to develop a power source for an artificial heart, so reliability was key. The company’s engines also powered deep-space exploration vehicles for NASA and for national security applications for the US Department of Energy.

Mass production

In 2005, Infinia set out to design a version of the Stirling engine that could convert solar thermal energy into electricity. In 2007, a prototype was developed that could be mass-manufactured at automotive scale.

J.D. Sitton, CEO of Infinia, understood that, for the solar power industry to achieve its potential, it must operate on “a much more scalable, production-capital-efficient basis than current technologies or business models allow.” For this reason, Infinia designed a solar power-generation appliance that could be mass-produced wherever industrialized production capabilities exist.

The company also believes that suppliers to the auto industry would be eager to switch from producing parts for the auto industry to producing them for the up-and-coming solar industry.

Choosing to produce the Infinia Solar System on auto assembly lines was an easy decision because “we use the same input materials, very similar design tolerance and nearly identical production processes,” Sitton explained. “We also were attracted to the inherent scalability of the automotive production model as well as its global presence.”

The Infinia Solar System was designed to be manufactured on auto assembly lines. Photo courtesy of Infinia.

The company is swinging into full-scale production and expects to have an annual capacity of approximately 200 MW within a year, with plans for dramatic expansion over the next few years. The auto suppliers undoubtedly have been hurt by the falloff in the auto industry and are “quick to understand the opportunity this represents to them,” Sitton noted. On the flip side, he added, these suppliers operate on a worldwide basis, so “the upset in Detroit isn’t expected to undermine [their] ability to meet their obligations to us or to threaten our production model.”

By taking the proven Stirling engine and ensuring that the production is truly scalable, Sitton said it was an “aha moment” when he realized that the company could “stamp ’em out like Chevrolets and sling ’em into the market like Maytags.”

Starting with just a handful of workers, the company has grown to 140 employees in just over 20 years.

How It Works

Infinia’s solar product uses the Stirling engine and a dish-style solar concentrator to harvest sunlight and turn it into electricity. In principle, the engine is an externally heated machine in which heat is introduced at the “hot” end of a closed volume containing a working fluid – usually a gas, and in Infinia’s case, helium – and extracted at the other, or “cold,” end. A piston separates the gas at the hot end from that at the cold end.

The “hot” is solar energy, concentrated at approximately 400× and focused on the hot end of the engine by a dish-style concentrator. The “cold” is provided by an automotive-style closed-loop cooling system. The solar energy heats the helium on the hot end, causing it to expand, and the cooling system causes the helium at the cold end to contract. Together, these forces cause the piston to move toward the cold end. As the piston moves, the gas on the hot end cools and on the cold end heats up to the point at which the piston travels in the other direction.

The Stirling engine uses the piston motion to create cyclical pressure waves, which drive a linear alternator and generate electricity. The engine is designed so that it accomplishes the task without any lubrication, and with no wear items or life-limiting components.

The technology is in contrast to photovoltaics (PV) technologies and products that dominate the market. The Infinia Solar System is thermal, whereas PV uses a photoelectric process. In a photoelectric process, light strikes a photoactive material, causing electrons to be released. In the case of PV, the photoactive material is usually a form of highly processed silicon arranged so that voltage is maintained and electrons flow in a desired direction.

Although PV products and systems are ubiquitous, Infinia’s CEO, J.D. Sitton, points out that they are noted for their modest conversion efficiencies and capital intensive production processes.

In contrast, many of the major components of the Infinia Solar System can be made on auto manufacturers’ production lines. These include its:

• Heat drive, which includes the Stirling engine, the receiver and the cooling system.

• Reflector, which is made from sheet-molded compound – the same material and process used by some automakers to make seats and mirror bodies.

• Chassis, which provides structural integrity and optical accuracy and is made using the same materials and processes as most automobile chassis.

• Biaxial drive, which enables the product to track the sun reliably and accurately. Although the gear ratios are constant, the biaxial drive unit is made of the same materials used to make automotive transmissions and other equipment.

• Power electronics package, which is included to ensure that the solar system can safely connect to, and operate in conjunction with, electric grids worldwide. The components used in this kit are very similar to the electrical components used in cars, computers and other forms of power generators.

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