Engineers from Stanford University (California, USA) They have created an optical concentrator, called Agile, which helps solar systems to capture more light even on a cloudy day and without the need to be directly pointed at the Sun.
Researchers have successfully designed and tested this ingenious lensing device that can efficiently collect light from all angles and concentrate it to a fixed output position.
Photovoltaic panels work best when sunlight shines directly on them. To capture as much energy as possible, many solar panels actively rotate toward the Sun as it moves across the sky. This makes them more efficient, but also more expensive and complicated to build and maintain than a fixed system.
At Stanford University, engineering researcher Nina Vaidya designed a ingenious device that can effectively collect and concentrate light that strikes it, regardless of the angle and frequency of that light.
It is a completely passive system: it does not require power to trace the source and has no moving parts. With no position-dependent optical focus and no need for tracking systems, concentrating light is much easier.
The device, named AGILE (Axially Graded Index Lens), is apparently simple. It looks like an inverted pyramid with the tip cut off. Light enters the square, tiled top from any angle and is funneled down to create a brighter point at the exit.
High system efficiency
In their prototypes, the researchers managed to capture more than 90% of the light hitting the surface and create exit points three times brighter than the incoming light.
Installed on a panel above solar cells, these concentrators could make solar arrays more efficient and capture not only direct sunlight, but also diffuse light that is scattered in the atmosphere land.
Placing a layer of AGILE hubs on top of the panels could replace the current encapsulation that protects the solar arrays, eliminate the need to track the Sun, create space for cooling and circuitry between the narrow pyramids of individual devices, and what’s more important, reduce the amount of solar cell surface needed to produce power and thus reduce costs.
And the uses are not limited to ground-based solar installations: if applied to solar arrays being sent into space, a layer AGILE could concentrate the light without solar tracking and provide the necessary protection against radiation.
The same principle as a magnifying glass under the sun
The basic premise of AGILE is similar to using a magnifying glass to burn leaves using sunlight. The lens of the magnifying glass concentrates the sun’s rays at a point.
But with a magnifying glass, the focal point moves like the sun does. Vaidya and Solgaard found a way to create a lens that takes in rays from all angles but always concentrates the light in the same starting position.
Vaidya and Solgaard determined that, in theory, it would be possible to collect and concentrate scattered light using an engineering material that smoothly increases its refractive index, a property that describes how fast light travels through a material, causing the light to bend and curve toward a focal point. On the surface of the material, the light hardly bends. When it got to the other side, it would be nearly vertical and in focus.
An ideal AGILE has, at its front, the same refractive index as air and gradually increases: the light bends in a perfectly smooth curve. But in a practical situation, that ideal AGILE will not exist.
For prototypes, researchers have layered different glasses and polymers that deflect light to varying degrees, creating what is known as graded index material. The layers change the direction of the light in steps rather than a smooth curve, which the researchers say is a good approximation to the ideal AGILE. The sides of the prototypes are mirrored, so any light going in the wrong direction is bounced back out.
One of the biggest challenges was finding and creating the right materials. The AGILE prototype’s material layers let a broad spectrum of light through, from near-ultraviolet to infrared, and deflect that light increasingly toward the exit with a wide range of refractive indices, something not seen in nature. nor in today’s optical industry.
After exploring many materials, creating new manufacturing techniques, and testing multiple prototypes, the researchers came to AGILE designs that worked well using commercially available polymers and glasses.
The AGILE also It has been manufactured by 3D printing in the authors’ previous work, which created lightweight, flexible engineered polymeric lenses with nanometer-scale surface roughness.
Vaidya hopes that AGILE designs can be used in the solar industry and beyond. AGILE has several potential applications in areas such as laser coupling, display technologies, and lighting, such as solid-state lighting, which is more energy efficient than older lighting methods.
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