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

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Utilization of solar energy that reaches the earth via photovoltaic systems is becoming a major challenge to meet the ever-increasing demand for energy. The answer must be given 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 require them to face the light source. Recently, researchers at Stanford University have designed a new pyramid-shaped optical lens that can efficiently capture and focus light, regardless of the angle of incidence and light intensity, on a cell. It captures up to 90% of the light and the output light intensity is three times greater than that received. Simple, inexpensive, flexible and scalable manufacturing techniques for their implementation pave the way for a revolution in the world of solar cells and laser technology.

Currently, a solar panel does not convert all the energy it receives into electricity. In addition to the losses during the process, the panel’s performance depends to a large extent on its composition, its orientation and its inclination relative to the light source, the Sun.

In fact, the theoretical yield limit for a panel is 31%. With amorphous silicon solar panels, the efficiency is usually between 6 and 9%, which is quite low. Polycrystalline panels have an efficiency between 13 and 18%. This is the most commonly used type of panel. Finally, with monocrystalline solar panels, the yield can be 16 to 24%. In addition, a southern orientation and a 30 ° slope are the optimal conditions for maximum performance. 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 stationary system.

In this context, engineering researcher Nina Vaidya and her specialist supervisor Olav Solgaard, professor of electrical engineering, at Stanford University have designed a pyramid-shaped optical lens that can focus sunlight at all angles on a solar cell so it can collect energy efficiently throughout the day, even under clouds. Their work is published in the journal Microsystems and nanotechnology.

AGILE: misleadingly simple

The device that researchers call AGILE – the Axially Graded Index Lens – is deceptively simple. It looks like a pyramid upside down with the tip cut off. Light enters the square, tiled top from any angle and is channeled downward to create a brighter spot when it comes out.

The basic principle behind AGILE is therefore similar to the use of a magnifying glass when it is used, for example, to burn a dry leaf, which concentrates the sun’s rays into a smaller, lighter spot. But with a magnifying glass, the focal point moves as the Sun does. Vaidya and Solgaard found a way to create a lens that captures rays from all angles, but still focuses the light at the same starting position, and without having to move the lens to face the Sun.

They stated that in theory it would be possible to collect and focus scattered light using a material that gradually increases the refractive index – a property that describes the speed at which light travels through a material – causing the light to bend towards a focal point. At the surface (input) of the material, the light would hardly change direction. When it reached the other side (exit), it would be almost vertical and focused.

Solgaard said in a statement: The best solutions are often the simplest ideas. An ideal AGILE has at the very front the same refractive index as air, and it increases gradually – the light follows a perfectly smooth curve “.

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

To the prototypes, the researchers added different glasses and polymers that “bend” light to varying degrees, creating what is called a material with a graded index. The layers change the direction of light in steps instead of a smooth curve, as the theory predicted. Nevertheless, the authors consider this design to be the best approximation of the “ideal AGILE”. The sides of the prototypes are mirrored so that any light going in the wrong direction is thrown out again.

Vaidya points out: One of the biggest challenges has been finding and creating the right materials Effectively, the layers of material in the AGILE prototype allow a wide range of light to pass through, from near ultraviolet to infrared, increasingly bending this light outwards with a wide range of refractive indices, never before seen in nature or in an industrial perspective. These materials used should also be compatible with each other – if a glass expanded in response to heat at a different rate than another, the whole unit could crack – and strong enough to be shaped and remain sustainable.

In their prototypes, the researchers were able to capture more than 90% of the light hitting the surface and create “spots” at the exit, three times stronger than the incoming light. Installed in a layer of solar cells, they could make solar panels more efficient and capture not only direct sunlight but also diffused light from the atmosphere, depending on the Earth’s weather conditions and seasons.

Large-scale potential

The top layer of AGILE could replace the existing enclosure that protects the solar panels. This design could also eliminate or reduce the need to track the Sun, create space for cooling and circuits between the shrinking pyramids of individual units, and most importantly, reduce the amount of surface area needed to generate power – and therefore reduce the cost. Vaidya hopes that AGILE lenses can be used in the solar industry and other areas, such as laser coupling, display technologies and solid-state lighting (more energy efficient than other methods of ‘lighting’).

Different stages in the fabrication of the graduated index glass pyramid: When in optical contact with a solar cell, the pyramid in the last step (lower right corner) absorbs and concentrates most of the incident light and appears dark. © Nina Vaidya

Applications are also not limited to terrestrial photovoltaic systems: if solar panels are applied to the room, an AGILE layer can both concentrate the 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 heat concentrators has been very rewarding. Abundant and affordable clean energy is a critical component in solving pressing climate and sustainability challenges, and we must catalyze engineered solutions to make it a reality. “.

Source: Microsystems & Nanoengineering

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