Axially graded AGILE lens acts as nontracking solar concentrator

Jan. 13, 2014
Researchers at Stanford University have designed and fabricated an efficient axially graded-index lens (AGILE) solar concentrator that accepts sunlight from all angles (which allows it to operate even in diffuse light), eliminating the need for tracking the sun.

Researchers at Stanford University (Stanford, CA) have designed and fabricated an efficient axially graded-index lens (AGILE) solar concentrator that accepts sunlight from all angles (which allows it to operate even in diffuse light), eliminating the need for tracking the sun. AGILE can achieve passive concentration for solar incidence angles from the full 2π steradians (180°) of the sky compared to less than tens of degrees for a typical compound parabolic concentrator. In fact, AGILE’s simulated and experimental performance matches closely with the nontracking theoretical maximum cosine theta incidence limit.

In the AGILE concentrator, light enters the system through a larger aperture of low refractive index, goes through a graded-index material, and is then absorbed in a high-index material with smaller aperture. AGILE is a reversible system that can work both as a concentrator or a diffuser. For an air (refractive index of 1) to silicon (index of 3.5) concentrator, for example, the theoretical concentration factor—the square of the refractive index ratio (3.5/1)2—is 12.25, but the architecture is not limited to these values. Higher concentrations of even tens of Suns can be achieved with alternate materials and lower than the full 180° acceptance angles. A first demonstration of AGILE using transparent UV-curable polymeric materials ranging in index from 1.4 to 1.6 and apertures that decreased from 7 to 5 mm (accepting almost all 2π incidence angles) improved efficiency by a concentration factor of 2. AGILE reduces the active solar-cell area and hence cost, provides perfect antireflection and encapsulation, allows cells to be spatially separated to provide space for circuitry and heat sinks, and can be fabricated to conform to curved surfaces as well. Contact Nina Vaidya at [email protected].

About the Author

Gail Overton | Senior Editor (2004-2020)

Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.

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