Unique solar panel design captures up to 90% light, even under the cloud

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The use of solar energy that reaches the earth, through photovoltaics, has become a major challenge to meet the growing energy demand. The response must be made in a sustainable and ecological way, in the context of climate change. Unfortunately, the most commonly installed panels have an efficiency between 13 and 24%, and have to deal with the light source. Recently, researchers at Stanford University designed a new pyramid-shaped optical lens that can effectively collect and focus light, regardless of the angle of incident and light, into a solar cell. It captures up to 90% of the light and the output light intensity is three times greater than received. Simple, inexpensive, flexible and scalable manufacturing techniques for their implementation, pave the way for a revolution in the world of photovoltaics and laser technology.

Currently, a photovoltaic panel does not convert all the energy it receives into electricity. In addition to the losses during the process, the performance of the panel depends heavily on its composition, its orientation and its inclination in relation to the light source, the Sun.

In fact, the theoretical yield limit on a panel is 31%. With amorphous silicon solar panels, the efficiency is usually between 6 and 9%, which is relatively low. Polycrystalline panels have efficiencies between 13 and 18%. This is the most commonly used panel type. Finally, in monocrystalline solar panels, the yield can be 16 to 24%. In addition, southern orientation and 30 ° inclination are the best conditions for maximum performance. Also, to capture as much energy as possible, many solar panels are actively rotating 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 non -stop system.

In this context, at Stanford University, engineering researcher Nina Vaidya, and her thesis supervisor Olav Solgaard, professor of electrical engineering, designed a pyramid-shaped optical lens that can focus on sunlight under any what is the angle of the solar cell, which enables it to collect energy efficiently throughout the day, even under the cloud. Their work was published in the journal Microsystems and Nanoengineering.

AGILE: deceptively simple

The device, which researchers call AGILE – for the Axially Graded Index Lens – is deceptively simple. It looks like an inverted pyramid with a cut end. Light enters the square, tiled top from any angle and is channeled downwards to create a brighter area to exit it.

So the basic principle behind AGILE is similar to using a magnifying glass when used to burn dry leaves for example, concentrating the Sun’s rays into a smaller, brighter area. But with a magnifying glass, the focal point will act as the Sun does. Vaidya and Solgaard found a way to make a lens that would capture rays from all angles, but still focus the light at the same exit position, and not have to move the lens to face the Sun.

They determined that, in theory, it is possible to collect and focus scattered light using a material that gradually increases the refraction index – a property that describes the speed at which light moves through a material – causes that the light will rotate toward a focal point. Above the material (entrance), the light can hardly change direction. When it reaches the other side (exit), it is almost upright and focused.

Solgaard said in a statement: The best solutions are usually the simplest ideas. An ideal AGILE has, in the long run, the same refractive index as air and it slowly increases – the light follows a perfectly smooth curve. “.

Principle of operation of the pyramid lens. © Nina Vaidya and Olav Solgaard, 2022 (Edited by Laurie Henry for Trust My Science)

For the prototypes, the researchers placed different glasses and polymers that “bent” light to different levels, creating a so-called graded-index material. The layers change the direction of the light in steps instead of a smooth curve as predicted in theory. However, the authors consider this design to be the best estimate of the “ideal AGILE”. The sides of the prototypes are mirrored, so that any light that goes in the wrong direction is reflected back.

Vaidya points out: One of the biggest challenges is finding and producing the right materials “. Effectively, the layers of material in the AGILE prototype allow a wide spectrum of light to pass through, from near ultraviolet to infrared, and bend that light more out with a wide variety. -different refractive indices, which have never been seen in nature, nor in the industrial point of view.These materials used must also be compatible with each other – if a glass is expanded in response to heat at a different rate than else, the whole device can be flexible – and strong enough to form and remain durable.

In their prototypes, the researchers captured more than 90% of the light hitting the surface and created “spots” at the exit, three times brighter than incoming light. Installed in a layer on top of solar cells, they can make solar panels more efficient and capture not only direct sunlight, but also scatter light from the atmosphere, depending on the conditions of the times and seasons of the Earth.

Great potential

The AGILE top layer can replace the existing encapsulation that protects the solar panels. This design can also eliminate or reduce the need to track the Sun, create space for cooling and circuitry between the reduced pyramids of individual devices, and above all, reduce the amount of surface required. to generate power – and therefore reduce costs. Vaidya hopes that AGILE lenses can be used in the solar industry and other fields, such as laser coupling, display technologies and solid state lighting (more energy efficient than other ‘lighting’ methods).

Different stages in making the graduate index glass pyramid: when in optical contact with a solar cell, the pyramid in the last stage (lower right corner) will absorb and concentrate most of the incident light and appear dark . © Nina Vaidya

Also, the devices are not limited to terrestrial solar installations: when applied to solar panels sent into space, an AGILE layer can concentrate light without solar tracking and provide the necessary protection against radiation.

Finally, Vaidya concludes: Being able to use these new materials, these new manufacturing techniques and this new AGILE concept to create better solar concentrators will be very rewarding. Abundant and cheap clean energy is a critical part of solving urgent climate and sustainability challenges, and we need to catalyze engineered solutions to make this a reality. “.

Source: Microsystems & Nanoengineering

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