I have a question regarding solar panels

[conscious evolution]

Actually not really about solar.

Seeing how visible light is only a portion of the electromagnetic spectrum,are there any panels that utilize the other parts of the spectrum?Areas like the radio,microwaveIR or UV frequencies?

Seems to me if you could use radio as a source you could point one at a cell tower and clean house.

[phantom power]

1. Sure, you can capture any photon and turn it into electricity.

The energy density passing through any given area is far from equal, at different wavelengths. Earth's atmosphere is fairly transparent at the visible wavelengths, and our sun's blackbody spectrum peaks in the visible. So, it's no mystery why you see a lot of focus on that region.

But there was this recent development that I get a kick out of, capturing in the infrared using actual antennas instead of bandgap.

http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=115&topic_id=128101&mesg_id=128101

[NNN0LHI]

2. Not enough power or directionality to do you any good

Now if you were able to rig some kind of collector in front of this baby with about a couple of Kilowatts passing through it you might be able to do something?



This bad mamma jamma would cook a turkey if you could get it close enough to it without going blind first.

Shame on it.

Don

[IntravenousDemilo]

3. And that's not even to mention...

...that we're being bombarded constantly from outer space by a wide variety of cosmic rays, far more than from any cell tower. If we could harness that...

[phantom power]

4. Very little energy there.

[lfairban]

5. Don't think the cell tower will work.

Even though it is putting out MegaWatts of energy, you can't capture a significant amount of it unless you are only a few feet away.

Remember that the energy of light is proportional to the frequency, so IR, radio and microwaves wouldn't work nearly as well even if solar cells could use them.

According to what I read here, they can't.

When a photon is absorbed, its energy is given to an electron in the crystal lattice. Usually this electron is in the valence band, and is tightly bound in covalent bonds between neighboring atoms, and hence unable to move far. The energy given to it by the photon "excites" it into the conduction band, where it is free to move around within the semiconductor. . .

A photon need only have greater energy than that of the band gap in order to excite an electron from the valence band into the conduction band. However, the solar frequency spectrum approximates a black body spectrum at ~6000 K, and as such, much of the solar radiation reaching the Earth is composed of photons with energies greater than the band gap of silicon. These higher energy photons will be absorbed by the solar cell, but the difference in energy between these photons and the silicon band gap is converted into heat (via lattice vibrations — called phonons) rather than into usable electrical energy.

So, if you create a photocell that will work with IR, it won't do a good job with the visible light. If you hit a standard photocell with UV that has greater energy, it won't do any more good than the visible light would have. If you design the photocell for UV, none of the visible light will be effective.

Thought I am certain that I don't understand everything in the article, I believe the answer to your question:

Seeing how visible light is only a portion of the electromagnetic spectrum,are there any panels that utilize the other parts of the spectrum?Areas like the radio,microwaveIR or UV frequencies?

No there aren't, there could be but the cells are uncommon or non-existent. The cells could be created, but if they do not exist it is because no one has seen sufficient need to create them.

[conscious evolution]

6. Thanks for the info

Someone asked me that the otherday and it seemed to make sense.
Oh well.

[TheWraith]

13. Actually a cell tower isn't putting out anything close to that.

Cellular phone towers measure in the watts. Nothing broadcasts in the megawatts except for the very largest big-city TV stations.

[kristopher]

7. I'm not sure if this is directly related to the OP question, but it might be.

MIT opens new 'window' on solar energy
Cost effective devices expected on market soon

Elizabeth A. Thomson, News Office
July 10, 2008

Imagine windows that not only provide a clear view and illuminate rooms, but also use sunlight to efficiently help power the building they are part of. MIT engineers report a new approach to harnessing the sun's energy that could allow just that.

The work, to be reported in the July 11 issue of Science, involves the creation of a novel "solar concentrator." "Light is collected over a large area and gathered, or concentrated, at the edges," explains Marc A. Baldo, leader of the work and the Esther and Harold E. Edgerton Career Development Associate Professor of Electrical Engineering.

As a result, rather than covering a roof with expensive solar cells (the semiconductor devices that transform sunlight into electricity), the cells only need to be around the edges of a flat glass panel. In addition, the focused light increases the electrical power obtained from each solar cell "by a factor of over 40," Baldo says.

Because the system is simple to manufacture, the team believes that it could be implemented within three years--even added onto existing solar-panel systems to increase their efficiency by 50 percent for minimal additional cost. That, in turn, would substantially reduce the cost of solar electricity.

* Fact sheet: MIT's solar concentrators

In addition to Baldo, the researchers involved are Michael Currie, Jon Mapel, and Timothy Heidel, all graduate students in the Department of Electrical Engineering and Computer Science, and Shalom Goffri, a postdoctoral associate in MIT's Research Laboratory of Electronics.

"Professor Baldo's project utilizes innovative design to achieve superior solar conversion without optical tracking," says Dr. Aravinda Kini, program manager in the Office of Basic Energy Sciences in the U.S. Department of Energy's Office of Science, a sponsor of the work. "This accomplishment demonstrates the critical importance of innovative basic research in bringing about revolutionary advances in solar energy utilization in a cost-effective manner."

Solar concentrators in use today "track the sun to generate high optical intensities, often by using large mobile mirrors that are expensive to deploy and maintain," Baldo and colleagues write in Science. Further, "solar cells at the focal point of the mirrors must be cooled, and the entire assembly wastes space around the perimeter to avoid shadowing neighboring concentrators."

The MIT solar concentrator involves a mixture of two or more dyes that is essentially painted onto a pane of glass or plastic. The dyes work together to absorb light across a range of wavelengths, which is then re-emitted at a different wavelength and transported across the pane to waiting solar cells at the edges.

In the 1970s, similar solar concentrators were developed by impregnating dyes in plastic. But the idea was abandoned because, among other things, not enough of the collected light could reach the edges of the concentrator. Much of it was lost en route.

The MIT engineers, experts in optical techniques developed for lasers and organic light-emitting diodes, realized that perhaps those same advances could be applied to solar concentrators. The result? A mixture of dyes in specific ratios, applied only to the surface of the glass, that allows some level of control over light absorption and emission. "We made it so the light can travel a much longer distance," Mapel says. "We were able to substantially reduce light transport losses, resulting in a tenfold increase in the amount of power converted by the solar cells."

This work was also supported by the National Science Foundation. Baldo is also affiliated with MIT's Research Laboratory of Electronics, Microsystems Technology Laboratories, and Institute for Soldier Nanotechnologies.

Mapel, Currie and Goffri are starting a company, Covalent Solar, to develop and commercialize the new technology. Earlier this year Covalent Solar won two prizes in the MIT $100K Entrepreneurship Competition. The company placed first in the Energy category ($20,000) and won the Audience Judging Award ($10,000), voted on by all who attended the awards.

http://web.mit.edu/newsoffice/2008/solarcells-0710.html

[lfairban]

8. I saw that.

It looks like a cool idea.

[conscious evolution]

9. It doesn't appear to be related

but it is a welcome innovation none the less.

[kristopher]

10. I'm not sure

I'm not sure because they wrote of using different colored dyes. One obvious possible reason for that would be to capture different wavelengths of light.

[jberryhill]

11. Here's what you have to play with:

There are multi-bandgap cells that mop up various parts of the spectrum, but those are for area-critical applications, since it doesn't pay to add that much more complexity outside of the peak range.

And, of course, the peak energy of the sun corresponds to the visible spectrum, for reasons which should be obvious.

If you are talking about picking up other sources of electromagnetic energy, such as radio transmissions, you are talking about extremely low power levels. Yes, obviously there are devices capable of picking up radio signals - in fact we call them "radios" - but you will notice that in order to provide an appreciable audio output, they require a powered amplifier.

[conscious evolution]

15. DOH!!!

Radios huh.Never heard of 'em!!Must be some new fangled technology.


When I have a brain fart they are usually pretty good ones.

[phantom power]

12. There was this interesting bit on multi-bandgap with Indium Nitride from 2002:

To my knowledge, this never went anywhere.

ScienceDaily (Nov. 19, 2002) — BERKELEY, CA — Researchers in the Materials Sciences Division (MSD) of Lawrence Berkeley National Laboratory, working with crystal-growing teams at Cornell University and Japan's Ritsumeikan University, have learned that the band gap of the semiconductor indium nitride is not 2 electron volts (2 eV) as previously thought, but instead is a much lower 0.7 eV.

The serendipitous discovery means that a single system of alloys incorporating indium, gallium, and nitrogen can convert virtually the full spectrum of sunlight -- from the near infrared to the far ultraviolet -- to electrical current.

http://www.sciencedaily.com/releases/2002/11/021119072756.htm

[One_Life_To_Give]

14. Forget Cell Towers, High Tension lines

For real power you want to harness the radiated fields from the big high tension lines. One farmer setup an aircore transformer in his barn and powered the whole farmhouse with it. Guess it worked for a few years before the power company tracked down why the efficiency of that particular transmission line was so low.

[conscious evolution]

16. I remember that

He took it all the way to the USSC and won.That decision is why people can make their own descramblers for satellites and other radio signals.