At one time people thought electricity was a fluid - hence the “flowing” of electrical “current.” Electrical theory has brought us the computer revolution, among other advances, because scientists and engineers figured out how to automatically control the flow of electricity based on varying conditions. Improvements in electronic technology continue to give us products that were merely imagined in sci-fi movies just a few decades ago.
At the same time, the field of fluid mechanics keeps flowing along, albeit with less fanfare than its flashier counterpart. If you think it’s just hydraulics and pneumatics, you may be surprised to learn that researchers are finding ways to automatically manipulate fluids to change their properties based on certain conditions. Sometimes electricity is used to change the shape of a droplet of liquid, allowing a system to direct natural sunlight to different parts of a building.
Not Smoke and Mirrors … Heat and Mirrors
More recently, Glint Photonics has been working on a self-tracking solar concentrator that uses a reflective cladding similar to that used in fiber optic cables. These “mirrors” only reflect light at certain angles. I asked Dr. Peter Kozodoy, founder and CEO of Glint Photonics, to explain how it works. He told me, “The cladding is a transparent layer, and only reflects light at certain angles via total internal reflection (the same mechanism at work in optical fibers). What the adaptive material does is locally change refractive index, which allows the focused light to enter the glass at the required angles for total internal reflection.”
Sunlight that’s concentrated by the lenslet array produces heat; that heat causes the reflective material to change its properties. The end result is that all of the incoming sunlight is directed onto the PV cell, regardless of its original angle of incidence.
Image courtesy of Glint Photonics
Concentrated Photovoltaics
This optofluidic device is intended for super efficient solar cells used in concentrated solar systems, not flat-panel rooftop solar arrays. Concentrated photovoltaics use highly efficient but very expensive solar cells, along with a magnifying glass to concentrate a large area of sunlight onto a small PV cell. Because the cell is so small, the tracking device must be extremely precise, making it quite costly. Glint’s self-tracking solar concentrator can be used by itself with no additional tracking system, or it can be used in conjunction with an inexpensive single or dual-axis tracker.
You might wonder why any mechanical tracking device would be used at all in a so-called “self-tracking” system. Shine a flashlight perpendicular to a surface and look at the beam. Now shine it at an angle and you’ll see the beam covering a wider area. Both beams have the same light energy, but the perpendicular beam concentrates it over a smaller area. The big advantage of the self-tracker is that the mechanical tracking system can keep the array perpendicular to the sunlight … more or less … but doesn’t need to be highly precise. That helps reduce the cost of the tracker. But will the money you save by using a low-cost tracker be enough to offset the cost of adding this device? At this point, it's too early to tell.
Glint Photonics has received funding from the Advanced Research Projects Agency for Energy (ARPA-E). The grant will allow the company to move from proof of concept to a near-commercial scale prototype. No word yet on when a production model could see the light of day, so to speak, but I’ll keep an eye on it.
Through the Looking Glass
I’m fascinated by recent advances in dynamic lenses and mirrors based on fluid mechanics. Whether this technology will have a significant impact on concentrated PV remains to be seen, but if nothing else the basic research will produce some interesting spin-off technology. As someone who just got his first prescription for bifocals, I’d like to see dynamic lenses incorporated into eyeglasses or contact lenses.