Engineers at Stanford University in California have developed an optical concentrator named AGILE that boosts solar energy capture, even on cloudy days, without the need to track the Sun directly.
Researchers have designed and tested this clever lensing device, capable of gathering light from all directions and concentrating it toward a fixed exit point with high efficiency.
Solar panels perform best when sunlight hits them directly. To maximize energy, many systems actively rotate to follow the Sun as it moves across the sky. While this increases efficiency, it also adds cost and complexity compared with stationary setups.
Nina Vaidya, an engineering researcher at Stanford, notes that AGILE is a remarkable device that can effectively collect and concentrate light regardless of angle or frequency.
AGILE operates as a completely passive system, needing no power to monitor the source and featuring no moving parts. Concentrating light becomes simpler because there is no need for position-dependent optical focus or tracking mechanisms.
The device, called AGILE, short for Axial Graduated Index Lens, has a simple appearance. It resembles an inverted pyramid with a truncated tip. Light enters at the top, which is open to light from any angle, and is funneled downward to create a brighter exit spot.
High system efficiency
In prototype tests, the team captured more than 90 percent of the light striking the surface and produced exit points that were three times brighter than the incident light.
Mounted above solar cells, these concentrators can make solar arrays more productive by capturing not only direct sunlight but also diffused light scattered through the atmosphere.
Positioning an AGILE hub layer over the panels can replace the existing encapsulation that protects solar arrays, removing the need to chase the Sun, providing space for cooling and circuitry between the narrow pyramids of individual devices, and crucially reducing the required solar cell area to generate power, which lowers costs.
The applications extend beyond ground installations. If applied to solar arrays sent into space, AGILE can concentrate light while offering protection against radiation without sun tracking.
A principle akin to a magnifying glass under sunlight
The core idea behind AGILE is similar to using a magnifying glass to focus sunlight on a single spot as it burns leaves. In a typical magnifying lens, the focal point follows the Sun. Vaidya and Solgaard found a method to design a lens that receives rays from any angle yet consistently concentrates light at the same initial location.
In theory, materials could be engineered to uniformly raise the refractive index, guiding light toward a fixed focal point. In practice, the ideal AGILE would require a perfectly smooth index change, which does not exist in real-world materials.
For prototypes, the researchers layered different glasses and polymers to deflect light in varying degrees, creating a graded directory material. The layers gradually change light direction instead of forming a perfect smooth curve, providing a close approximation to the ideal AGILE. The outer edges are mirrored to reflect any light that travels in the wrong direction.
One major challenge was identifying suitable materials. The AGILE layers allow a broad spectrum of light, from ultraviolet to near infrared, to pass through and bend toward the exit with a wide range of refractive indices not commonly used in today’s optics industry.
After exploring numerous materials, developing new manufacturing methods, and testing several prototypes, the team found AGILE designs that work well with commercially available polymers and glasses.
AGILE can also be produced with 3D printing. In their earlier work, the authors developed lightweight, flexible engineered polymer lenses with nanometer-scale surface roughness.
Vaidya hopes AGILE designs will find applications in the solar industry and beyond. The concept holds promise for lighting technologies such as laser coupling, imaging, and solid-state lighting, which is more energy efficient than older methods.
Reference work on the topic was published by Stanford researchers in late June 2022, describing how the new optical device helps solar arrays focus light even through clouds and diffuse skies.
Environment-related research notes and updates are retained for institutional records and ongoing development, with ongoing input from engineering teams at Stanford.