Good Thinking

Sunlight-concentrating ball illuminates dark places

Sunlight-concentrating ball il...
The prototype solar concentrator, inside its protective dome
The prototype solar concentrator, inside its protective dome
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Asst. Prof. Yoo Seongwoo (left) and Dr. Charu Goel with the solar concentrator
Asst. Prof. Yoo Seongwoo (left) and Dr. Charu Goel with the solar concentrator
The prototype solar concentrator, inside its protective dome
The prototype solar concentrator, inside its protective dome

If you worked in a dingy, windowless environment, it would be nice (and energy-efficient) if you could get natural daylight "piped in" from outside. An experimental device does exactly that, in a new compact and robust form.

First of all, there are already "solar concentrators" that gather and reroute sunlight to dim rooms. With the exception of some small home-use units, such devices typically incorporate large curved mirrors, plus they utilize heavy-duty motors and exposed gearing to pan with the sun as it moves across the sky.

Seeking a simpler yet still effective alternative, scientists at Singapore's Nanyang Technological University started with a commercially available clear acrylic ball, then aligned the end of a plastic optical fiber with the back of it. When the ball was facing toward the sun, it focused the incoming rays of sunlight onto its backside, where they were picked up by the fiber. It proceeded to carry the light along its length, emitting it out of its other end.

A transparent polycarbonate dome surrounds the prototype, protecting it from the elements. Additionally, a GPS- and clock-enabled chip is used to control two small motors that move the optical fiber to different locations along the surface of the ball throughout the day. In this way, the receiving end of the fiber is always at the back of the ball, relative to the position of the sun in the sky.

Asst. Prof. Yoo Seongwoo (left) and Dr. Charu Goel with the solar concentrator
Asst. Prof. Yoo Seongwoo (left) and Dr. Charu Goel with the solar concentrator

When tested in a pitch-black room, the device was found to exceed the luminous efficacy of an off-the-shelf LED bulb, and to provide light output similar to that of a larger and more expensive conventional solar concentrator. It is hoped that a commercial version of the technology could incorporate a pole-mounted ball, along with an LED bulb beside the light-emitting end of the fiber, which would automatically switch on as the sun goes down.

"Due to space constraints in densely populated cities, we have intentionally designed the daylight harvesting system to be lightweight and compact," says the lead scientist, Asst. Prof. Yoo Seongwoo. "This would make it convenient for our device to be incorporated into existing infrastructure in the urban environment."

The research is described in a paper that was recently published in the journal Solar Energy.

Source: Nanyang Technological University via AlphaGalileo

Perhaps I'm misunderstanding here, but it appears that concentrator would deliver at most the amount of sunlight that falls on one not-that-big acrylic ball (which is also not that light). So each ball might deliver 50-100w of light -- nice for a small room, but not enough for a bigger spaces unless you have dozens or hundreds of them. Ironically, the idea of a movable input window under computer control might work really well for the mirror-based concentrators the inventors want to replace. Move the fiber entrance, not the whole mirror.
As it "focused the incoming rays of sunlight onto its backside", did the sun shine out of its behind?
Expanded Viewpoint
This "idea" is either not explained very well in the article due to confusions by all parties concerned, or it's bogus. How is there any advantage to using a spherical shape for the light ray collector, if it has to be "aimed" at the light source? Why not just use a hemisphere, with the fiber optic cable mounted at the high point opposite the flat portion? That way, you could have many light collectors side by side, with them feeding their output into separate fiber optic cables, which could then be routed to a different location!
A better idea, might be to use a parabolic shape with the cable mounted at the focal point and putting a reflective coating on the rearward side of the parabola. And instead of a parabola, perhaps a simple funnel with a 45 degree angle to it would work just as well, without having to be concerned about generating a precise parabolic shape. In other words, these guys need to go back to the drawing board!
Oh, cute quip there, 88!!
Aaron MacTurpen
Not to brag, but I did this in Skyrim like five years ago.
I like the really low tech version of this a lot better. Take one transparent 2 liter soda bottle. Fill with water. Drill hole in roof/ceiling, seal bottle in place. This is actually used in third world tropical countries where the only available sources of indoor light are windows that admit malaria-carrying mosquitos along with the light or fire of some sort (which requires fuel and costs money). No fancy light pipe but water and plastic, by they are actually enough to trap a very substantial fraction of incident daytime sunlight and transmit it, somewhat diffusely, ot the interior. Again, close to equivalent to 100 W light bulb, several of these can easily light up a room, but unlike the design above, which will IMO NEVER EVER recoup the energy required to build it, it is as close to "free" as one can reasonably get.
Clock and GPS ???? wouldn't a photo sensor(or three) be simpler and cheaper? Regardless, this seems silly. A solar panel connected to a bulb is a lot simpler still.
If only someone could invent an inexpensive luminous glass ball that would be available to people all over the world.
I put 3 of commercially available solar tubes in a dark kitchen, bathroom and porch. Basically it is a high strength plastic dome with a highly polished mirror finish tube that telescopes down into a room and has a glass skylight type difuser. On all but the darkest days and right up until sunset they really brighten the room up. No GPS or motors needed.

Note: I did this just before having the house re-roofed with metal so I got good seals around them.
Adrian Akau
Not practical. Less expensive and simpler to use solar collector, wires, light.
I love natural sunlight indoors.