Engineers at Stanford University in California have developed an optical concentrator named AGILE that boosts solar energy capture. It works effectively even on cloudy days and does not require direct sun pointing to convert light into usable energy.
Researchers report that this clever lensing device can collect light from all directions and concentrate it toward a fixed exit point for efficient utilization.
Photovoltaic panels traditionally peak in efficiency when sunlight hits them straight on. To maximize energy harvest, many solar arrays track the sun, rotating as it moves across the sky. While this approach increases efficiency, it adds cost and complexity to manufacturing, installation, and maintenance compared to stationary configurations.
Nina Vaidya, a Stanford engineering researcher, explains that AGILE can effectively gather and concentrate light regardless of the incident angle or light frequency, making it a versatile passive solution.
Crucially, AGILE is a completely passive system with no power requirements for monitoring the light source and no moving parts. This makes concentrating light simpler because there is no need for position-dependent focusing or tracking hardware.
The device, named AGILE (Axial Graduated Index Lens), has a compact, simple appearance. It resembles an inverted pyramid with a truncated tip. Light enters the frame from any direction, the top surface is tiled to collect light, and it funnels it downward to form a brighter exit point.
High system efficiency
In prototype studies, researchers achieved the capture of more than 90 percent of the light striking the surface and produced exit points roughly three times brighter than the incoming light.
When installed above solar cells, these concentrators can boost overall panel efficiency by capturing not only direct sunlight but also diffused light scattered in the atmosphere, improving performance in less-than-ideal conditions.
Placing an AGILE hub layer over existing panels could replace traditional encapsulation protections, eliminate the need for sun tracking, and create space for cooling and circuitry between the narrow pyramids of individual devices, all while reducing the total solar cell area required to generate power and cutting costs.
Beyond ground installations, the layer could be applied to solar arrays deployed in space, concentrating light while offering radiation protection without sun tracking.
Same principle as a magnifying glass under the sun
The basic idea behind AGILE is akin to using a magnifying glass to focus sunlight onto one spot. A traditional lens concentrates rays at a focal point that shifts with the sun’s position.
Vaidya and Solgaard demonstrated a lens that accepts rays from all angles yet consistently concentrates light at the same fixed exit position. In theory, an engineered material could uniformly increase its refractive index to bend and concentrate light toward a focal point without moving parts. On the surface, light would bend gently; by the time it reaches the other side, it would be nearly vertical and in focus.
An ideal AGILE would match the refractive index of air at the front and gradually increase it through the material. In practice, perfect homogeneity is not possible, but researchers created strong approximations with graded index materials. The prototype edges are mirrored to reflect any light that travels in the wrong direction back toward the exit.
One major challenge was identifying and fabricating suitable materials. The layered material stack in the AGILE prototype allows a broad spectrum of light, from ultraviolet to near infrared, to pass through while progressively steering rays toward the exit. The materials push beyond common refractive indices used in traditional optics, broadening the range of light behavior to achieve efficient concentration.
After exploring numerous materials, developing new manufacturing methods, and testing several prototypes, the research team found AGILE designs that work well with commercially available polymers and glasses. The concept also leveraged 3D printing to create lightweight, flexible engineered polymer lenses with nanometer-scale surface roughness in related work.
Researchers see AGILE as having broad potential in the solar industry and beyond. Possible applications span lighting and imaging technologies, laser coupling, and solid-state lighting that can be more energy-efficient than legacy methods.
Reference work is available in public science news coverage published by Stanford News dated June 27, 2022, which outlines the development and testing of the device for solar arrays and focused-light applications. [Attribution: Stanford News Release, 2022].
…
Notes: the project considers future materials and manufacturing approaches to enable scalable production for practical solar use and beyond.