New optical system might assist photo voltaic arrays focus mild, even beneath clouds

Even with the spectacular and steady advances in photo voltaic applied sciences, the query stays: How can we effectively acquire vitality from daylight coming from various angles from dawn to sundown?

Photo voltaic panels work greatest when daylight hits them straight. To seize as a lot vitality as potential, many photo voltaic arrays actively rotate in the direction of the solar because it strikes throughout the sky. This makes them extra environment friendly, but additionally costlier and complex to construct and keep than a stationary system.

These lively methods might not be needed sooner or later. At Stanford College, engineering researcher Nina Vaidya designed a sublime system that may effectively collect and focus mild that falls on it, whatever the angle and frequency of that mild. A paper describing the system’s efficiency, and the idea behind it, is the quilt story within the July subject of Microsystems & Nanoengineering, authored by Vaidya and her doctoral advisor Olav Solgaard, professor {of electrical} engineering at Stanford.

“It’s a totally passive system – it doesn’t want vitality to trace the supply or have any shifting elements,” mentioned Vaidya, who’s now an assistant professor on the College of Southampton, UK. “With out optical focus that strikes positions or want for monitoring methods, concentrating mild turns into a lot less complicated.”

The system, which the researchers are calling AGILE – an acronym for Axially Graded Index Lens – is deceptively easy. It appears to be like like an upside-down pyramid with the purpose lopped off. Mild enters the sq., tile-able high from any variety of angles and is funneled all the way down to create a brighter spot on the output.

Of their prototypes, the researchers have been capable of seize over 90% of the sunshine that hit the floor and create spots on the output that have been thrice brighter than the incoming mild. Put in in a layer on high of photo voltaic cells, they might make photo voltaic arrays extra environment friendly and seize not solely direct daylight, but additionally diffuse mild that has been scattered by the Earth’s environment, climate, and seasons.

A high layer of AGILE might substitute the present encapsulation that protects photo voltaic arrays, take away the necessity to monitor the solar, create area for cooling and circuitry to run between the narrowing pyramids of the person units, and, most significantly, cut back the quantity of photo voltaic cell space wanted to supply vitality – and therefore cut back the prices. And the makes use of aren’t restricted to terrestrial photo voltaic installations: if utilized to photo voltaic arrays being despatched into area, an AGILE layer might each focus mild with out photo voltaic monitoring and supply needed safety from radiation.

The AGILE array system. Be aware that the AGILE doesn’t have metallic reflective sidewalls within the video in order that the graded index materials will be visualized. (Video by Nina Vaidya and Xuan Wu)

Envisioning the proper AGILE

The fundamental premise behind AGILE is much like utilizing a magnifying glass to burn spots on leaves on a sunny day. The lens of the magnifying glass focuses the solar’s rays right into a smaller, brighter level. However with a magnifying glass, the point of interest strikes because the solar does. Vaidya and Solgaard discovered a method to create a lens that takes rays from all angles however all the time concentrates mild on the identical output place.

“We needed to create one thing that takes in mild and concentrates it on the identical place, even because the supply modifications route,” mentioned Vaidya. “We don’t need to should maintain shifting our detector or photo voltaic cell or shifting the system to face the supply.”

Vaidya and Solgaard decided that, theoretically, it will be potential to gather and focus scattered mild utilizing an engineered materials that easily elevated in refractive index – a property that describes how rapidly mild travels by means of a fabric – inflicting the sunshine to bend and curve in the direction of a focus. On the floor of the fabric, the sunshine would hardly bend in any respect. By the point it reached the opposite aspect, it will be nearly vertical and targeted.

“The most effective options are sometimes the only of concepts. A perfect AGILE has, on the very entrance of it, the identical refractive index because the air and it step by step will get larger – the sunshine bends in a superbly easy curve,” mentioned Solgaard. “However in a sensible state of affairs, you’re not going to have that ideally suited AGILE.”

From concept to actuality

For the prototypes, the researchers layered collectively completely different glasses and polymers that bend mild to completely different levels, creating what’s referred to as a graded index materials. The layers change the sunshine’s route in steps as a substitute of a easy curve, which the researchers discovered to be a superb approximation of the best AGILE. The perimeters of the prototypes are mirrored, so any mild going within the fallacious route is bounced again in the direction of the output.

One of many greatest challenges was discovering and creating the proper supplies, Vaidya says. The fabric layers within the AGILE prototype let a broad spectrum of sunshine, from near-ultraviolet to infrared, move by means of it and bend that mild more and more in the direction of the output with a variety of refractive indices, which isn’t seen in nature or the current optics trade. These supplies used additionally needed to be suitable with one another – if one glass expanded in response to warmth at a unique fee than one other, the entire system might crack – and strong sufficient to be machined into form and stay sturdy.

“It’s certainly one of these ‘moonshot’ engineering adventures, going proper from concept to actual prototypes,” mentioned Vaidya. “There are numerous concept papers and nice concepts on the market, nevertheless it’s onerous to show them into actuality with actual designs and actual supplies pushing the boundaries of what was deemed not possible earlier than.”

After exploring many supplies, creating new fabrication methods, and testing a number of prototypes, the researchers landed on AGILE designs that carried out effectively utilizing commercially accessible polymers and glasses. AGILE has additionally been fabricated utilizing 3D printing within the authors’ prior work that created light-weight and design-flexible polymeric lenses with nanometer-scale floor roughness. Vaidya hopes the AGILE designs will be capable to be put to make use of within the photo voltaic trade and different areas as effectively. AGILE has a number of potential purposes in areas like laser coupling, show applied sciences, and illumination – resembling solid-state lighting, which is extra vitality environment friendly than older strategies of lighting.

“Utilizing our efforts and information to make significant engineering methods has been my driving power, even when some trials weren’t understanding,” mentioned Vaidya. “To have the ability to use these new supplies, these new fabrication methods, and this new AGILE idea to create higher photo voltaic concentrators has been very rewarding. Ample and reasonably priced clear vitality is a crucial a part of addressing the pressing local weather and sustainability challenges, and we have to catalyze engineering options to make {that a} actuality.”