Researchers at Stanford University have used 3D printing to develop a novel device that could help boost solar arrays’ energy-capturing capabilities and remove the need for mechanized tracking systems.

Shaped like a tipless inverted pyramid, the team’s Axially Graded Index Lens (AGILE) device captures over 90% of the light it’s exposed to and funnels it in a way that trebles its brightness. Compared to existing solar arrays, which follow the sun across the sky, the AGILE can also catch light passively from any angle, lending it the potential to help make solar panels smaller, cheaper, and more efficient.

“We wanted to create something that takes in light and concentrates it at the same position, even as the source changes direction,” explains the device’s developer Nina Vaidya. “It’s a completely passive system – it doesn’t need energy to track the source or have any moving parts. Without optical focus that moves positions or need for tracking systems, concentrating light becomes much simpler.”

Different stages of the graded index glass pyramid fabrication: when in optical contact with a solar cell, the pyramid at the final step (bottom right corner) absorbs and concentrates most of the incident light and appears dark. Image via Nina Vaidya.
Different stages of the graded index glass pyramid fabrication: when in optical contact with a solar cell, the pyramid at the final step (bottom right corner) absorbs and concentrates most of the incident light and appears dark. Image via Nina Vaidya.

Pursuing solar power efficiency 

Seeing as photovoltaic systems’ sunlight-absorbing capabilities are dependent on them directly facing the sun, many are fitted with solar trackers. In a single-axis set up, these systems rotate back and forth in a single direction. With dual-axis trackers, on the other hand, they tend to use a mirror to redirect sunlight towards a stationary receiver, as a means of maximizing light-panel exposure. 

Both of these ‘active’ systems move in tandem with the sun, and generate more energy than stationary alternatives, but according to the Stanford engineers, they’re also pricier and more complicated to build. To facilitate the more efficient capture of solar energy, the team has therefore come up with a device made from a material that’s designed to passively concentrate scattered light at a focal point. 

Known as AGILE, this device operates like a magnifying glass, in that it focuses the sun’s rays into a smaller, brighter point, but instead of moving with the sun, it channels rays from all angles to the same output. By replacing the silicon used to encapsulate existing solar modules with a layer of these devices, the researchers say it’s possible to generate more energy from cheaper, compact solar panels. 

“The best solutions are often the simplest of ideas,” explains Vaidya’s doctoral advisor Olav Solgaard. “An ideal AGILE has, at the very front of it, the same refractive index as the air and it gradually gets higher – the light bends in a perfectly smooth curve.” Though he adds, “in a practical situation, you’re not going to have that ideal AGILE.”

Nina Vaidya measuring the experimental performance of optical concentrators under a solar simulator. Photo via Nina Vaidya.
Stanford researcher Nina Vaidya measuring the experimental performance of her optical concentrator under a solar simulator. Photo via Nina Vaidya.

AGILE solar energy capture 

In order to produce their initial AGILE polymeric lens prototypes in 2018, the engineers used a combination of SLA and wax 3D printing. However, the team has since moved on to a method that enables the deposition of glass and polymer into a graded index material, with layers capable of changing a light beam’s direction in steps, instead of in a smooth curve. 

Utilizing this material, the researchers have now managed to create ‘mirrored’ devices, in which any light heading in the wrong direction, is bounced back towards their output. During testing, these prototypes have also demonstrated the ability to channel light in such a way that it trebles its brightness. As such, it’s said that the devices could eventually be fitted to ordinary solar panels, as a means of enabling them to capture light scattered by the Earth’s atmosphere, weather and seasons.

According to Vaidya, the main challenge to creating such devices is formulating the right material. The plastic and glass used to make the team’s prototypes had to be compatible with each other, as if one expanded in response to heat at a different rate to the other, the whole device could crack. That said, the team has ultimately come across a formula that allows for the creation of lenses with nanometer-scale features, lending it solar panel storage and backlit display-powering potential. 

“To be able to use these new materials, these new fabrication techniques, and this new AGILE concept to create better solar concentrators has been very rewarding,” concludes Vaidya. “Abundant and affordable clean energy is a vital part of addressing the urgent climate and sustainability challenges, and we need to catalyze engineering solutions to make that a reality.” 

“Using our efforts and knowledge to make meaningful engineering systems has been my driving force, even when some trials were not working out.”

A rendering of AGILE devices assembled into an array. Image via Stanford University.
A rendering of AGILE devices assembled into an array. Image via Nina Vaidya.

Advancing solar energy storage 

A significant amount of research is currently being poured into 3D printable materials with enhanced solar energy-storing capabilities. Earlier this year, Oak Ridge National Laboratory (ORNL) announced that a team of its researchers are investigating the potential of metal halide perovskites for 3D printing high-performance solar batteries

Similarly, start-up T3DP has previously experimented with using its patented technologies to 3D print perovskite-based solar panels. Modeled on an exact replica of a fly’s eye, the firm’s copper-plated hexagon scaffolds were said to be capable of harnessing twice as much energy as conventional solar panels. 

Elsewhere, the technology has also been deployed to enable the creation of solar-powered devices with other applications than clean energy generation. Researchers based in China and Singapore, for example, have 3D printed solar water purification devices at such a high standard in the past, that they’ve met World Health Organization standards. 

The researchers’ findings are detailed in their paper titled “3D printed optics with nanometer scale surface roughness,” which was co-authored by Nina Vaidya and Olav Solgaard.

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Featured image shows Nina Vaidya measuring the experimental performance of optical concentrators under a solar simulator. Photo via Nina Vaidya.





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By GIL