Energy

Pyramid lenses catch light from any angle to boost solar cell efficiency

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A new passive technology can collect sunlight striking it from any angle and bend it towards the solar cell beneath
A new passive technology can collect sunlight striking it from any angle and bend it towards the solar cell beneath
AGILE is an array of inverted-pyramid-shaped lenses that concentrates sunlight onto a solar cell
Nina Vaidya
An artist's impression of an AGILE array
Nina Vaidya
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Solar cells are an increasingly important source of renewable energy, but there’s still room for improvement. Stanford engineers have now developed a pyramid-shaped lens that can focus sunlight from any angle onto a solar cell, keeping it collecting power from sunrise to sunset.

Solar cells work best in direct sunlight, which means many of them might only have a few good hours of energy generation in them per day. Others maximize their working time by actively moving to follow the Sun across the sky, but that consumes energy and adds mechanical complexity.

For the new study, the Stanford team set out to develop a passive technology that can collect sunlight that strikes it from any angle, and concentrates it towards the solar cell beneath. The end result is an array of inverted-pyramid-shaped structures that the team calls Axially Graded Index Lenses (AGILE), which would form a layer that replaces the protective top surface of a solar cell.

AGILE is an array of inverted-pyramid-shaped lenses that concentrates sunlight onto a solar cell
Nina Vaidya

In tests, the AGILE prototypes were able to capture more than 90 percent of the light that hit its surface, focusing it so that it’s three times brighter by the time it reaches the solar cell. The team says that this system could improve the efficiency of solar cells by allowing them to collect indirect sunlight, as well as boosting their output in less than ideal weather and conditions.

AGILE sounds simple enough, but the engineering behind it is quite complicated. Each little pyramid is made up of a stack of different glasses and polymers with different refractive indices – essentially, each layer bends the incoming light to a different degree. The top layer has a low refractive index to allow the light to enter from any angle, but each step down bends it a little more, until it focuses on the solar cell below. The sides are mirrored to bounce any wayward light back where it needs to go.

An artist's impression of an AGILE array
Nina Vaidya

These multiple materials also allow the device to capture a wide spectrum of light, from near-ultraviolet to infrared. The team also had to make sure the materials worked well together – for instance, that they expand in heat at similar rates so as not to crack the device. Even using several materials, the team demonstrated that AGILE can be 3D printed.

The team says that the new system could help expand the places where solar energy can be used, reducing both the cost and the land needed. AGILE could even improve solar cells for spacecraft.

The research was published in the journal Microsystems & Nanoengineering.

Source: Stanford University

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10 comments
windykites
I am wondering how you can 3D print refractive glass. It looks like it could be expensive. the sun moves in an arc, so a linear light channel should do the job. Also this device may cause hot spots by concentrating the light.
Captain Danger
I would be interested in how much more electricity can be generated compared to a regular solar cell.
At what price point would this become worth while?
Holger
> the sun moves in an arc, so a linear light channel should do the job.

That is correct, but with the azimuth (sun angle) changing with the seasons you're back to needing something...like a pyramid.
Thomas W Harris
This technology seems brilliant, but it appears from the artist rendering that only the outside rows would receive maximum sun on other than the top layer. Don't the interior lenses get shaded by those blocking the sun rays? We are doing some solar projects in the desert that would benefit if this would work. Thomas Harris, Attorney, Palm Desert, CA.
Expanded Viewpoint
Something you're not taking into account, Thomas, is that we are not in the vacuum of space where there are no air borne particles to deflect the light rays from the sun. In a vacuum, shaded areas are black because no light is being bounced around corners, the rays always travel in a straight line. In an atmosphere, water vapor and various suspended particulates cause those rays to bounce around and soften the contrast between light and dark areas. The atmosphere sort of "glows", and we're in the middle of that glowing gas.
czechster
Similar to ship lenses used in old wooden ships to light up the cargo holes.
Gregg Eshelman
Such concentrating things have been experimented with since the 1970's. http://www.greenrhinoenergy.com/solar/technologies/pv_concentration.php

Do a google image search for photovoltaic concentrator mirrors
Vinny van demon
Global Skylights, magnifying glass and bubble plastic come to mind....now over to you Stanford! :)
Malcolm Jacks
I hope this can improve existing sola panels. I have had my sola panels for nearly 10 years now, because i have 4 panels on my front roof and 4 panels on my back roof, I only get the sun in the morning on one side, and in the afternoon on the other side.
ljaques
The final effectiveness vs the added cost will reveal whether or not it comes to life, but I doubt it.